Guide · Updated 08/07/2026
Changes you must report — and changes worth reporting
Some changes you are legally required to tell the CMS about; others are optional but can change the figure in your favour. Knowing which is which — and always reporting in a way that leaves a record — avoids both penalties and overpayment.
Paying parents: changes you must report
| Change | Why it matters |
|---|---|
| Address | A legal requirement within 7 days. Failing to notify without reasonable excuse is a criminal offence under the information regulations, punishable by a fine. |
| Change of employer / becoming self-employed | Affects income basis and any deduction from earnings order |
| Benefits starting or stopping | Switches you to/from the £7 flat rate |
| Income increases of 25%+ — only if your calculation is based on current income | Where the calculation rests on current income (not HMRC historic income), you must report an increase of 25% or more within 14 days (Information Regulations 2008, reg 9A; DMG 19050). Where it rests on historic income, there is no legal duty to report increases (DMG 19051) — though decreases are always worth reporting, since only a report changes the figure. |
| Child comes to live with you / relevant other children | Changes who is paying whom, and the income reduction for other children |
Providing false information to the CMS, or failing to provide required information, is a criminal offence (s.14A Child Support Act 1991). Beyond prosecution risk, discovered concealment poisons every future discretionary decision in your case. Play it absolutely straight — the legitimate routes on this site are more effective anyway.
Changes worth reporting (either parent)
- Income moves 25% or more (up or down) from the figure in use — the calculation only changes if someone reports it with evidence; see Income & HMRC.
- Shared care pattern changes — a new court order, school change, or the child staying more or fewer nights. See shared care.
- Pension contributions start or change — evidence them to secure the deduction.
- A child leaves full-time non-advanced education — liability for that child ends; keep an eye on Child Benefit status, which the CMS follows.
- New variation-relevant facts — contact costs, prior debts, the other parent's unearned income. See variations.
How to report so it sticks
Report promptly
Supersessions generally take effect from the date you report, not the date the change happened. Sitting on a drop in income costs you money you will not get back.
Put it in writing
Phone calls are summarised (sometimes wrongly) in case notes. Follow any call with a message via your online account or letter: what you reported, the date, the evidence enclosed. This record wins later MRs and complaints.
Chase the decision
A reported change should produce a decision letter. No letter within a reasonable time means the report may not have been actioned — a classic source of phantom arrears and a proper subject for complaint.
Sources
| Source | Type | Date | Credibility |
|---|---|---|---|
| GOV.UK — Child Maintenance Service (report a change) | Official guidance | Current | High |
| Child Support Act 1991, s.14A (offences) | Primary legislation | As amended | High |
| Child Support Information Regulations 2008 (incl. reg 9A) | Primary legislation (SI) | As amended | High |
| CMS Decision Makers Guide, Vol 2, Ch 19 (reporting income changes) | Official internal guidance (not law) | Current published version | High for CMS practice |