Understanding your situation

The Child Maintenance Service has issued a maintenance calculation or decision you believe is wrong. CMS uses HMRC's latest tax-year data as the default — which can be significantly out of date if you are a contractor, have irregular earnings, or have changed jobs recently. CMS calculations are governed by the Child Support Act 1991 (as amended) and the Child Support Maintenance Calculation Regulations 2012. Standard rates are percentages of gross weekly income up to a weekly cap, with variations available for specific circumstances. Common appeal grounds: - Income used is outdated or incorrect - Shared-care bands are misapplied - A variation is needed for special expenses (contact costs, boarding school fees, prior-relationship debt repayment) - Additional-income variation should apply to the paying parent - Diversion of income is suspected (the paying parent has artificially reduced declared income) The appeal is strictly two-stage — you must request Mandatory Reconsideration first (within 30 days), and only appeal to the First-tier Tribunal if that is rejected (within 1 month of the reconsideration notice). Skipping the Mandatory Reconsideration stage is not permitted. Poorly drafted reconsideration requests that do not cite the correct Regulations provisions are routinely rejected, forcing escalation to Tribunal — where the 1-month clock is already running.

What you need to prepare

✓Copy of the CMS decision letter (with decision date)
✓Your grounds for disputing the decision
✓Supporting evidence: current PAYE slips, HMRC self-assessment, bank statements
✓Shared-care calendar showing actual overnight stays per year
✓For special-expenses variation: receipts for contact costs, school fee letters, debt documentation
✓For diversion-of-income allegations: Companies House records, accounts
✓Copy of any previous CMS calculations or decisions

⏰ Deadline

Mandatory Reconsideration: 30 days from the CMS decision. First-tier Tribunal appeal: 1 month from the Mandatory Reconsideration Notice. Late appeals may be accepted up to 13 months with good cause (discretionary). Always verify the current deadline wording on the CMS decision notice before counting days.

🏛️ Authority

Stage 1: Child Maintenance Service (part of the Department for Work and Pensions). Stage 2: First-tier Tribunal (Social Entitlement Chamber), HM Courts & Tribunals Service.

⚖️ Legal basis

Child Support Act 1991 (as amended). Child Support Maintenance Calculation Regulations 2012. Social Security Act 1998 (appeals framework). Tribunal Procedure (First-tier Tribunal) (Social Entitlement Chamber) Rules 2008. UK child maintenance regulations are amended periodically — verify current regulations before filing.

Expert tips

1Do Mandatory Reconsideration first — you cannot skip to Tribunal. A request for Tribunal without prior Mandatory Reconsideration will be rejected.
2Cite specific provisions of the applicable Regulations in the reconsideration — generic disputes are routinely rejected.
3For income disputes, attach current PAYE slips (last 3 months) and explain why HMRC's default data is no longer representative.
4For shared-care bands, attach an overnight calendar showing actual dates — don't rely on CMS's assumed 'pattern of care'.
5Variations are separate applications — if you need a variation, apply for it even while Mandatory Reconsideration is pending.
6Citizens Advice offers free assistance with CMS appeals — consider using them for a second pair of eyes on your grounds.
7Maintenance continues at the calculated amount during the appeal. If your appeal succeeds, CMS will recalculate and may refund — but don't stop paying.

Appeal CMS Child Maintenance Decision — Mandatory Reconsideration & Tribunal

Understanding your situation

What you need to prepare

Expert tips

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