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Free CMS Calculation Challenge Letter Template

The Child Maintenance Service (CMS) is the United Kingdom statutory body that calculates and enforces child maintenance under the Child Support Act 1991. Where a calculation is wrong on the facts, omits income, or fails to recognise special expenses, the paying or receiving parent can challenge it via four statutory routes — revision under section 16, mandatory reconsideration under section 28A, a variation application under the Child Support Maintenance Calculation Regulations 2012, or supersession under section 17. Our free UK template builds a structured challenge letter to CMS — sender identification, qualifying children, statutory route selected, brief grounds, and four Expert clauses on Regulation 34 / 69-71 additional income, Regulations 63-65 special expenses, the Smith v Smith diversion-of-income protocol, and the First-tier Tribunal appeal route under section 12 of the Social Security Act 1998.

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Child Maintenance Service Calculation Challenge
Child Support Act 1991  ·  CMS Reference CMS-2026-04-17/HALL-7748  ·  12 June 2026
Imogen Catherine Halloway
42 Mossbank Crescent, Didsbury, Manchester M20 6PR
07815 442098
i.halloway@example.co.uk
12 June 2026
Child Maintenance Service
PO Box 249
Mitcheldean GL14 9BG
0800 171 2345
CMS CALCULATION CHALLENGE - Child Support Act 1991 / SI 2012/2677
CMS Ref: CMS-2026-04-17/HALL-7748 | Decision dated: 14 May 2026
Dear Sir or Madam,

I write as Imogen Catherine Halloway, the RECEIVING PARENT (the parent with care within the Child Support Act 1991, the parent who receives the assessed maintenance), in connection with the Child Maintenance Service calculation issued on 14 May 2026 under reference CMS-2026-04-17/HALL-7748 in respect of the child or children of Matthew Edward Halloway. The current weekly amount is GBP 92.50 based on a historic gross weekly income figure of GBP 485.00.

This letter is the formal entry point for the following statutory route: VARIATION APPLICATION under section 28A and regulation 34 of the Child Support Maintenance Calculation Regulations 2012 (SI 2012/2677) - special expenses (regs.63-65) or additional income (regs.69-71), including the diversion-of-income ground at reg.71.

This letter constitutes the sender's STATEMENT OF CASE. The detailed evidence rubric and any variation grounds relied on are set out below.
1.
SENDER IDENTIFICATION AND CMS ARRANGEMENT
Sender: Imogen Catherine Halloway
Address: 42 Mossbank Crescent, Didsbury, Manchester M20 6PR
Telephone: 07815 442098
Email: i.halloway@example.co.uk
Role in the CMS arrangement: the RECEIVING PARENT (the parent with care within the Child Support Act 1991, the parent who receives the assessed maintenance)
Other parent: Matthew Edward Halloway
CMS reference number: CMS-2026-04-17/HALL-7748
Calculation decision date: 14 May 2026
Current weekly amount: GBP 92.50
Historic income figure used: GBP 485.00 gross weekly
2.
QUALIFYING CHILDREN
The CMS arrangement covers the following qualifying child or children:

Child 1: Sophia Rose Halloway  ·  DOB 18 April 2015
Child 2: Thomas Edward Halloway  ·  DOB 9 November 2017
3.
STATUTORY ROUTE OF THIS CHALLENGE
The sender pursues the following statutory route in connection with the calculation:

VARIATION APPLICATION under section 28A and regulation 34 of the Child Support Maintenance Calculation Regulations 2012 (SI 2012/2677) - special expenses (regs.63-65) or additional income (regs.69-71), including the diversion-of-income ground at reg.71

Variation application under regulation 34 of SI 2012/2677 modifies the historic gross weekly income figure to reflect special expenses (regs.63-65) or additional income (regs.69-71), including diverted income at reg.71.
4.
BRIEF GROUNDS OF THE CHALLENGE
Brief grounds:
The Child Maintenance Service calculation issued on 14 May 2026 uses an HMRC historic-income figure of GBP 485 gross weekly. The receiving parent's case is that the historic figure materially under-states the paying parent's true economic income. The paying parent is a director and sole shareholder of an IT consultancy company through which he provides services to a single corporate client; the company retains a substantial proportion of its earnings rather than declaring dividends, and the paying parent has accessed funds through a director's loan account on a non-arm's-length basis. The receiving parent invites CMS to apply the diversion-of-income ground under regulation 71 and to bring the substance of the paying parent's earnings into the calculation.

The detailed evidence rubric and any variation grounds are set out in the Expert sections below. The sender invites CMS to consider the evidence in the round and to issue a revised calculation. Where CMS upholds the existing calculation in whole or part, the sender will exercise the right of appeal to the First-tier Tribunal under section 12 of the Social Security Act 1998.
5.
INCOME EVIDENCE - REGULATION 34 + REGULATIONS 69-71
(A) STATUTORY HOOK. Regulation 34 of SI 2012/2677 is the gateway to variation grounds. The grounds engaged here fall under regulations 69-71 - additional income from undisclosed earnings, unearned income above GBP 2,500 a year, notional income from assets, and diversion of income at regulation 71.

(B) NATURE OF THE INCOME CONCERN. The income concern engaged in this challenge is: undisclosed or under-declared dividends from a controlled or close-family company that should be brought into the calculation under reg.71 (diversion of income) or reg.69 (unearned income above GBP 2,500 a year).

(C) EVIDENCE PACKAGE.
(i) Companies House filings for Halloway Consulting Ltd for the period from April 2023 to March 2026 - retained earnings increased from GBP 38,400 to GBP 142,800 against minimal dividend distribution; (ii) the most recent corporation tax return showing director's loan account drawdown of GBP 41,200 over the 12 months to March 2026; (iii) the paying parent's self-assessment return for 2025/26 showing dividends of GBP 2,400 - inconsistent with the company's profitability; (iv) the receiving parent's witness statement (separately filed) describing the company structure and the paying parent's pattern of drawing remuneration; (v) bank statement extracts (limited - the receiving parent does not have direct access) showing transfers between the company and the paying parent's personal account.

(D) HMRC HISTORIC INCOME LIMITATION. The CMS calculation is built on the HMRC historic-income figure for the most recent available tax year (SI 2012/2677 reg.4). Where the historic figure does not capture the substance of the paying parent's true economic income, regulations 69-71 provide the variation route. The sender's case is that the HMRC figure of GBP 485.00 is materially incomplete on the evidence set out above.

(E) STATUTORY THRESHOLD - GBP 2,500 UNEARNED INCOME. Under regulation 69, unearned income (dividends, interest, rents, royalties, overseas distributions) above GBP 2,500 a year is added to the calculation where it can be evidenced. The sender's evidence is that the paying parent has unearned income materially above the GBP 2,500 threshold.

Income evidence narrative:
The receiving parent invites CMS to write to the paying parent for the audited management accounts of Halloway Consulting Ltd for the period from April 2023 to March 2026, the director's loan account ledger, and the paying parent's personal bank statements for the same period. CMS's powers under SI 2012/2677 reg.4 to obtain HMRC data should be exercised in full. Where the paying parent declines to produce the requested evidence, the receiving parent invites CMS to draw an adverse inference under the protocol in Smith v Smith [2024] UKUT 234 (AAC).
6.
LIFESTYLE DISPARITY AND DIVERSION OF INCOME - SMITH V SMITH PROTOCOL
(A) STATUTORY HOOK - REG.71. Regulation 71 of SI 2012/2677 is the diversion-of-income ground. It engages where the paying parent has the ability to control the amount of income received (whether earned or unearned) and has unreasonably reduced the amount that would otherwise be available - typically by routing payments through a controlled company, a current partner, a family member, or a discretionary trust.

(B) SMITH v SMITH [2024] UKUT 234 (AAC). The Upper Tribunal in Smith v Smith (Child Support) [2024] UKUT 234 (AAC) is the leading authority on diversion of income via dividend manipulation in family-controlled companies. The UT reinforced the reach of reg.71 and articulated the evidential threshold the First-tier Tribunal should apply: where the substance of the arrangement is the paying parent's earnings, the form of the corporate or partner payment does not insulate the income from the calculation. The sender invites CMS to apply the Smith v Smith protocol on the evidence here.

(C) NJDB v JEG [2012] UKSC 21. The Supreme Court in NJDB v JEG [2012] UKSC 21 confirmed that lifestyle inconsistent with declared income may ground a variation where the FtT is satisfied on the evidence that the paying parent has additional income or notional income beyond the HMRC historic figure. The sender relies on the NJDB v JEG framework.

(D) LIFESTYLE EVIDENCE. The evidence relied on: a combination of high-value asset acquisition, premium travel, private education and private healthcare expenditure that cumulatively cannot be funded from the declared historic-income figure.

(E) LIFESTYLE NARRATIVE.
The paying parent's lifestyle since separation in October 2024 is materially inconsistent with the declared historic gross weekly income figure of GBP 485. The receiving parent's evidence: (i) the paying parent purchased a 4-bedroom detached property at 18 Beechwood Avenue, Hale Barns WA15 8TX in March 2025 for GBP 875,000 (HM Land Registry price-paid record) with a reported deposit of GBP 175,000; (ii) the paying parent acquired a 2024 Range Rover Sport on lease at a documented monthly cost of GBP 1,180 in May 2025; (iii) the paying parent has taken three international family holidays since separation (Maldives July 2025, Aspen February 2026, Mauritius April 2026), each at a documented cost above GBP 8,000; (iv) the paying parent's elder daughter from an earlier relationship was enrolled at Manchester Grammar School in September 2025 at annual fees of GBP 16,800; (v) the paying parent's current partner has not been documented as a substantial earner. These observable expenditure patterns cumulatively cannot be funded from a gross weekly income of GBP 485 over an annualised twelve-month period.

(F) DIVERSION ROUTE. The diversion route engaged is: a controlled or family-controlled company - dividends suppressed, retained-earnings strategy, director's loan account drawn down on a non-arm's-length basis (the classic Smith v Smith protocol).

(G) DIVERSION NARRATIVE.
The diversion route engaged here is the controlled company - Halloway Consulting Ltd is a single-director, single-shareholder company through which the paying parent provides IT consulting services to a single corporate client. The company retains earnings rather than distributing dividends, with the result that the paying parent's self-assessment historic-income figure is depressed. The substance of the arrangement is the paying parent's earnings; the form of the corporate retention does not change the economic position. The receiving parent invites CMS to apply the Smith v Smith [2024] UKUT 234 (AAC) protocol on the evidence here and to find under reg.71 of SI 2012/2677 that the paying parent has the ability to control the amount of income received and has unreasonably reduced that amount through corporate retention.

(H) APPLICATION TO THE CALCULATION. The sender invites CMS to find that the paying parent has the ability to control the amount of income received and has unreasonably reduced that amount through the route identified above, with the result that additional income should be brought into the calculation under reg.71.
7.
APPEAL PREPARATION - FTT BUNDLE INDEX, MRN WINDOW, SMITH V SMITH ROUTE
(A) STATUTORY ROUTE. Where CMS upholds the calculation in whole or part following mandatory reconsideration, the sender may appeal to the First-tier Tribunal (Social Entitlement Chamber - Child Support list) under section 12 of the Social Security Act 1998. The appeal is lodged on Form FtT3 (Notice of Appeal) within 30 days of the Mandatory Reconsideration Notice.

(B) MRN AND APPEAL DEADLINE. Upon receipt of the Mandatory Reconsideration Notice from CMS, the sender will diary the 30-day FtT appeal deadline.

(C) BUNDLE INDEX.
(i) Form FtT3 notice of appeal (to be filed if CMS upholds the calculation following mandatory reconsideration); (ii) CMS calculation decision letter dated 14 May 2026; (iii) any Mandatory Reconsideration Notice issued by CMS; (iv) this statement of case as refined for the FtT; (v) Companies House filings for Halloway Consulting Ltd; (vi) any forensic accountancy report on the diversion of income; (vii) HM Land Registry / DVLA / private-education / travel evidence; (viii) the receiving parent's witness statement; (ix) the children's particulars (Sophia Rose 11 and Thomas Edward 9); (x) the requested outcome (revised calculation reflecting true earnings).

(D) HEARING PREFERENCE. The sender invites the FtT to determine the appeal via: ORAL HEARING - short hearing before an FtT judge (typically half-day); appellant attends and may be accompanied by a representative; typically 20-28 weeks from valid appeal notice.

(E) UPPER TRIBUNAL ROUTE. Appeal from the FtT on a point of law lies to the Upper Tribunal (Administrative Appeals Chamber) under section 11 of the Tribunals, Courts and Enforcement Act 2007. The UT route is reserved for cases where the FtT has erred in law - for example, by misapplying the Smith v Smith reg.71 threshold or by failing to engage with the NJDB v JEG lifestyle evidence framework.

(F) R (KEHOE) v SSWP [2005] UKHL 48. The architecture confirmed by the House of Lords in R (Kehoe) v Secretary of State for Work and Pensions [2005] UKHL 48 confines enforcement to the statutory CMS route and the FtT / UT appeal route. The sender will not pursue a parallel civil claim and will rely on the statutory framework throughout.

(G) NO COSTS. The FtT has no general costs power - each party normally bears its own costs save in cases of unreasonable conduct.

Appeal narrative:
The receiving parent invites the FtT to convene an oral hearing in light of the disputed evidence on the corporate retention strategy and the lifestyle evidence package. The receiving parent will be represented (where funded) or attend in person; the paying parent should attend in person to answer the corporate retention questions. The receiving parent reserves the right to escalate to the Upper Tribunal under section 11 of the Tribunals, Courts and Enforcement Act 2007 if the FtT misapplies the Smith v Smith protocol or fails to engage with the NJDB v JEG framework.
8.
DOCUMENTS ENCLOSED
Pursuant to the request set out above, the sender encloses (or will produce on CMS request):

   (a) this statement of case;
   (b) a copy of the CMS calculation decision letter dated 14 May 2026;
   (c) the evidence package per variation ground relied on (corporate filings / dividend vouchers / partnership accounts / partner payroll records / HMRC self-assessment returns / bank statements / mortgage statements / school invoices);
   (d) (where lifestyle disparity is relied on) the lifestyle evidence schedule referred to in the Expert clause - HM Land Registry / DVLA / private-education invoices / travel evidence;
   (e) (where special expenses are relied on) the weekly expense breakdown with supporting receipts and statements.

The sender invites CMS to issue a revised calculation in accordance with the statutory route set out above. Where CMS upholds the existing calculation in whole or part following mandatory reconsideration, the sender reserves the right to appeal to the First-tier Tribunal under section 12 of the Social Security Act 1998 within the 30-day statutory window.
YOURS FAITHFULLY,
Imogen Catherine Halloway
Receiving parent (CMS arrangement)
Date: ____________________

Available as a print-ready PDF or an editable Microsoft Word (.docx) file.

What Is a CMS Calculation Challenge?

A Child Maintenance Service calculation challenge is the formal entry point for disputing a CMS decision in the United Kingdom. CMS calculates child maintenance using the paying parent's gross weekly income (taken from the most recent HMRC tax year), the number of qualifying children and the number of nights of overnight care. Where the calculation is wrong on the facts (income figure outdated, qualifying children misstated, shared-care threshold misapplied), the affected parent may challenge it. There are four statutory routes: revision under section 16 of the Child Support Act 1991 (CMS official error or fresh evidence within one month); mandatory reconsideration under section 28A (a precondition to a First-tier Tribunal appeal); variation application under regulations 63-71 of the Child Support Maintenance Calculation Regulations 2012 (SI 2012/2677); and supersession under section 17 (a forward-looking change of circumstances).

Variation grounds are split between paying-parent grounds and receiving-parent grounds. The paying parent typically raises special expenses under regulations 63-65 of SI 2012/2677 — contact costs, debt repayments incurred for the benefit of the family before separation, costs of supporting a disabled child, boarding-school fees and prior-court-order maintenance liabilities. The receiving parent typically raises additional income under regulations 69-71 — unearned income above GBP 2,500 a year (rental, dividend, savings interest), notional income from assets, and diversion of income at regulation 71. The leading United Kingdom authority on the diversion-of-income ground is Smith v Smith (Child Support) [2024] UKUT 234 (AAC); the Supreme Court framework on lifestyle inconsistency is NJDB v JEG [2012] UKSC 21.

Where the mandatory reconsideration is unsuccessful in whole or part, the affected parent may appeal to the First-tier Tribunal (Social Entitlement Chamber — Child Support list) under section 12 of the Social Security Act 1998. The notice of appeal (Form FtT3) must be lodged within 30 days of the Mandatory Reconsideration Notice. Appeal on a point of law lies further to the Upper Tribunal under section 11 of the Tribunals, Courts and Enforcement Act 2007. The Tribunal Procedure (First-tier Tribunal) (Social Entitlement Chamber) Rules 2008 (SI 2008/2685) govern the FtT bundle, evidence and hearing protocol. CMS is the respondent before the FtT but typically does not attend.

What's Covered in This Template

Our United Kingdom CMS calculation challenge letter template builds a structured challenge — sender identification, qualifying children, statutory route, brief grounds, and four Expert clauses on the variation grounds and the FtT appeal preparation.

Four Statutory Routes — s.16, s.28A, Variation, s.17

Pre-frames the four statutory challenge routes — revision under section 16 of the Child Support Act 1991 (CMS error or fresh evidence within one month), mandatory reconsideration under section 28A (precondition to an FtT appeal), variation application under SI 2012/2677, and supersession under section 17 (forward-looking change).

Paying-Parent vs Receiving-Parent Role Switch

Auto-switches the variation grounds based on the sender's role — special expenses (regulations 63-65) for the paying parent; additional income and diversion of income (regulations 69-71) for the receiving parent. Each side has different variation grounds open under United Kingdom child maintenance law.

Qualifying Children Repeatable Row

Captures every qualifying child by name, date of birth and parental responsibility status. CMS calculates per qualifying child under section 11 of the Child Support Act 1991 — the percentage rate scales with the number of children (12% for one, 16% for two, 19% for three or more).

Regulation 34 + 69-71 Additional Income (Expert)

Expert clause structures the additional-income challenge under regulation 34 (the gateway to variations) and regulations 69-71 — unearned income above GBP 2,500 a year (rental, dividends, savings interest), notional income from assets, and diversion of income at regulation 71. Evidence index for HMRC SA302s, Companies House filings, bank statements and Land Registry records.

Regulations 63-65 Special Expenses (Expert)

Expert clause structures the special expenses variation — contact costs (regulation 63), debt repayments for family-purpose loans incurred before separation (regulation 64), costs of supporting a disabled child, boarding-school fees and prior-court-order maintenance liabilities. Each category is subject to a weekly de minimis threshold and must be evidenced.

Smith v Smith Diversion-of-Income Protocol (Expert)

Expert clause incorporates the Upper Tribunal protocol in Smith v Smith (Child Support) [2024] UKUT 234 (AAC) on regulation 71 diversion of income — where the paying parent has the ability to control income (through a controlled company, current partner, family member or discretionary trust) and has unreasonably reduced it. Lifestyle evidence framed under NJDB v JEG [2012] UKSC 21.

FtT Appeal Preparation — s.12 Social Security Act 1998 (Expert)

Expert clause structures the First-tier Tribunal (Social Entitlement Chamber — Child Support list) appeal under section 12 of the Social Security Act 1998. Covers the 30-day Mandatory Reconsideration Notice window, Form FtT3 lodgement, bundle index and the Smith v Smith routing. Upper Tribunal appeal route under section 11 of the Tribunals, Courts and Enforcement Act 2007.

CMS Reference and Calculation Decision Date Capture

Records the CMS reference (printed on every calculation letter and on the CMS My Child Maintenance Case online account) and the date of the calculation decision being challenged. The mandatory reconsideration window runs from the decision date, not the date the letter was received.

Current Income Figure Disclosure

Captures the current historic gross weekly income figure CMS has applied (taken from HMRC for the most recent tax year). Where the figure does not match the paying parent's true economic income, the variation grounds in this letter are the way to challenge it under United Kingdom child maintenance law.

13-Month Discretionary Extension Window

Flags the CMS discretionary extension of the mandatory reconsideration window up to 13 months on good cause shown (postal delay, misdirection, illness). The letter expressly invites CMS to extend where the standard one-month window has passed.

Documents Enclosed Index

Pre-drafts a documents-enclosed index — the CMS calculation decision letter, HMRC SA302 / P60 / payslips, bank statements showing unearned income, Companies House records of director shareholdings, evidence of contact costs (travel receipts, contact-centre invoices), evidence of prior court-order maintenance, and evidence of disabled-child support costs.

Sender Address and Contact Block

Standard United Kingdom sender block — name, address, telephone, email — at the head of the letter. CMS routes correspondence by the CMS reference but the sender block is the primary identifier and is required on every page.

How to Build a CMS Calculation Challenge

Follow these steps to produce a structured CMS calculation challenge letter that lands the United Kingdom variation grounds and preserves the First-tier Tribunal appeal route.

  1. 1

    Confirm Your Role — Paying or Receiving Parent

    Different variation grounds are open to each side. The paying parent (non-resident parent) typically raises special expenses under regulations 63-65 of SI 2012/2677. The receiving parent (parent with care) typically raises additional income and diversion of income under regulations 69-71. The template auto-switches the grounds based on your role.

  2. 2

    Capture the CMS Reference and Decision Date

    The CMS reference is printed on every calculation letter and on the My Child Maintenance Case online account. The decision date is the date of the calculation letter being challenged — the mandatory reconsideration window runs from that date, not from receipt. Where post was slow, raise it in the brief grounds and ask CMS to extend on good cause.

  3. 3

    Pick the Statutory Route

    Mandatory reconsideration under section 28A is the standard route where you want to dispute the calculation and reserve the right to appeal to the First-tier Tribunal. Variation application is the route where you want to add or reduce income through the regulated grounds. Revision under section 16 corrects a CMS official error; supersession under section 17 reflects a change of circumstances going forward.

  4. 4

    List Every Qualifying Child

    CMS calculates per qualifying child under section 11 of the Child Support Act 1991. The percentage rate scales with the number of children — 12% of gross weekly income for one child, 16% for two, 19% for three or more. The receiving parent retains the calculation for every child the paying parent has parental responsibility for and who lives with the receiving parent.

  5. 5

    Write the Brief Grounds

    One or two paragraphs setting out the headline grounds for the challenge — the calculation is wrong on the facts, omits income, fails to recognise expenses, applies the wrong rate, or fails to reflect a change of circumstances. Detail goes into the Expert clauses; the brief grounds give CMS a roadmap on first read.

  6. 6

    Frame Additional Income Under Regs 34 + 69-71 (Expert)

    Expert clause for the receiving parent. Regulation 34 of SI 2012/2677 is the gateway to variations; regulations 69-71 are the additional-income grounds — unearned income above GBP 2,500 a year (rental, dividends, savings interest), notional income from assets, and diversion of income at regulation 71. Evidence: HMRC SA302s, Companies House filings, bank statements, Land Registry.

  7. 7

    Frame Special Expenses Under Regs 63-65 (Expert)

    Expert clause for the paying parent. Regulations 63-65 list the five special expense categories — contact costs (travel, contact centre fees), debt repayments for family-purpose loans incurred before separation, costs of supporting a disabled child, boarding-school fees and prior-court-order maintenance. Each is subject to a weekly de minimis threshold and must be evidenced.

  8. 8

    Build the Diversion-of-Income Case — Smith v Smith Protocol (Expert)

    Expert clause incorporating the Upper Tribunal protocol in Smith v Smith [2024] UKUT 234 (AAC). Regulation 71 catches income the paying parent has the ability to control but has unreasonably reduced — dividends withheld from a controlled company, wages booked to a current partner, retained earnings drawn through a director's loan account. Lifestyle inconsistency under NJDB v JEG [2012] UKSC 21.

  9. 9

    Preserve the FtT Appeal Route (Expert)

    Expert clause structures the First-tier Tribunal (Social Entitlement Chamber — Child Support list) appeal under section 12 of the Social Security Act 1998. The notice of appeal (Form FtT3) is lodged within 30 days of the Mandatory Reconsideration Notice. Bundle index and Smith v Smith framing for the FtT hearing. Upper Tribunal route under section 11 of TCEA 2007.

  10. 10

    Enclose Evidence and Sign the Letter

    Compile the documents-enclosed index — CMS calculation decision letter, HMRC SA302s, P60s, bank statements, contact-cost receipts, court-order copies — and sign the letter. File with CMS via post or upload through the My Child Maintenance Case online account. CMS acknowledges within 14 working days.

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Legal Considerations — CMS Calculation Challenge

Child maintenance in the United Kingdom is administered by the Child Maintenance Service (formerly the Child Support Agency) under the Child Support Act 1991 and the Child Maintenance and Other Payments Act 2008. The calculation framework is set by the Child Support Maintenance Calculation Regulations 2012 (SI 2012/2677). Challenges run through four statutory routes — revision, mandatory reconsideration, variation and supersession — with First-tier Tribunal appeal under section 12 of the Social Security Act 1998.

This template is for general information and does not constitute legal advice. CMS calculations involve substantive law on income, residence, shared care and the variation grounds, and the First-tier Tribunal appeal route turns on the statutory windows. Where the calculation involves controlled-company income, trust income, lifestyle inconsistency or diversion of income, specialist advice from a family solicitor with child support experience or a child maintenance advisor is recommended. Resolution maintains a directory of specialist family practitioners; the Child Poverty Action Group provides additional support to receiving parents pursuing variation applications.

Reviewed for the United Kingdom (England, Wales, Scotland, Northern Ireland)

Calculation Framework — Child Support Act 1991 + SI 2012/2677

The CMS calculation under the 2012 rules takes the paying parent's gross weekly income from HMRC for the most recent tax year, applies the percentage rate per qualifying child (12% / 16% / 19% under section 11 of the Child Support Act 1991), and adjusts for shared-care nights and relevant other children. The Child Support Maintenance Calculation Regulations 2012 (SI 2012/2677) govern income identification, shared-care adjustments and the variation grounds. The historic-income figure is reviewed annually; supersession under section 17 reflects forward-looking changes.

Variation Grounds — Regulations 34 + 63-71

Regulation 34 of SI 2012/2677 is the gateway to all variation grounds. Regulations 63-65 list the five paying-parent special expense categories (contact costs, family-purpose debt repayments, disabled-child support, boarding-school fees, prior-court-order maintenance), each subject to weekly de minimis thresholds. Regulations 69-71 list the receiving-parent additional-income grounds — unearned income above GBP 2,500 a year, notional income from assets, and diversion of income at regulation 71. The diversion-of-income ground engages where the paying parent has the ability to control income and has unreasonably reduced the amount that would otherwise be available.

Smith v Smith and the Diversion-of-Income Protocol

The leading United Kingdom authority on regulation 71 diversion of income is Smith v Smith (Child Support) [2024] UKUT 234 (AAC). Diversion engages where the paying parent has the ability to control income (whether earned or unearned) and has unreasonably reduced the amount that would otherwise be available — typically by routing payments through a controlled company, a current partner, a family member or a discretionary trust. The Supreme Court framework on lifestyle inconsistency in NJDB v JEG [2012] UKSC 21 confirms that observable lifestyle materially inconsistent with declared income can support a finding of additional or notional income. Detailed evidence — bank statements, HMRC SA302s, Companies House filings, Land Registry — is decisive.

First-tier Tribunal Appeal Route

Where CMS upholds the calculation in whole or part following mandatory reconsideration, the affected parent may appeal to the First-tier Tribunal (Social Entitlement Chamber — Child Support list) under section 12 of the Social Security Act 1998. The notice of appeal (Form FtT3) is lodged within 30 days of the Mandatory Reconsideration Notice. The Tribunal Procedure (First-tier Tribunal) (Social Entitlement Chamber) Rules 2008 (SI 2008/2685) govern the bundle, evidence and hearing protocol. Appeal on a point of law lies further to the Upper Tribunal (Administrative Appeals Chamber) under section 11 of the Tribunals, Courts and Enforcement Act 2007. CMS is the respondent before the FtT but typically does not attend; the FtT decides on the papers and the parent's oral evidence.

Frequently Asked Questions

Build Your CMS Calculation Challenge Letter

Produce a structured United Kingdom Child Maintenance Service calculation challenge letter — sender identification, qualifying children, statutory route under the Child Support Act 1991 (revision under section 16, mandatory reconsideration under section 28A, variation, or supersession under section 17), brief grounds, and four Expert clauses on the additional-income and special-expense variation grounds in the Child Support Maintenance Calculation Regulations 2012 (SI 2012/2677), the Smith v Smith [2024] UKUT 234 (AAC) diversion-of-income protocol, and the First-tier Tribunal appeal preparation under section 12 of the Social Security Act 1998. Files with CMS via post or the My Child Maintenance Case online account.

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