UK · CMS Formula
Free CSA Child Maintenance Calculator UK 2026
Estimate weekly, monthly, and yearly child maintenance payments using current CMS rules. · Verified from gov.uk
Reviewed by Abdul Rafay (verified against CMS formula and gov.uk) · Published May 2026 · Last verified: May 2026
Your income
Before income tax and National Insurance. Salary sacrifice and occupational scheme contributions are already reflected in your HMRC gross income figure.
About the children
Children living with you full-time in your household (e.g. from a new relationship). Reduces the gross income used in the calculation.
Monthly is estimated as weekly × 52 ÷ 12. There is no fixed calendar month amount.
Estimate only · Verify at gov.uk
Key facts
CMS rate for 1 child
12%
of gross weekly income
CMS rate for 2 children
16%
of gross weekly income
CMS rate for 3+ children
19%
of gross weekly income
Income cap
£3,000
gross per week
How Child Maintenance Is Calculated in the UK
Child maintenance is the regular payment a non-resident parent makes to the parent with primary care of the children. The Child Maintenance Service (CMS) calculates it from the paying parent's gross income, taken directly from HMRC.
CSA vs CMS: the formula changed in 2012
The old Child Support Agency (CSA) used net income after tax. The current Child Maintenance Service (CMS) uses gross income from HMRC, before tax and National Insurance. If you used an old CSA calculator, your estimate may differ.
| Gross weekly income | 1 child | 2 children | 3 or more |
|---|---|---|---|
| £200 | £24 | £32 | £38 |
| £400 | £48 | £64 | £76 |
| £600 | £72 | £96 | £114 |
| £800 | £96 | £128 | £152 |
| £1,000 | £120 | £160 | £190 |
| £1,500 | £180 | £240 | £285 |
| £2,000 | £240 | £320 | £380 |
| £3,000 (cap) | £360 | £480 | £570 |
Edge cases
UK CMS Child Maintenance Rules
- 01
CMS uses gross income, not net
The CMS takes the paying parent's gross income directly from HMRC, before tax and National Insurance. Salary sacrifice and occupational pension contributions are already reflected in your gross figure.
- 02
The CMS formula applies only up to £3,000 gross per week
The CMS formula applies only up to £3,000 gross per week (approximately £156,000 per year). The receiving parent can apply to court for a top-up order above the cap.
- 03
Shared care reduces the weekly payment
Overnight stays reduce the weekly amount: 1 night/week by one-seventh, 2 nights by two-sevenths, 3 nights by three-sevenths. 175+ nights per year usually cuts it by 50%.
- 04
Low income and benefits recipients pay a flat £7 per week
Paying parents with gross weekly income of £7 to £100 pay a flat £7/week. Parents on prescribed benefits also pay the £7 flat rate, not nil.
- 05
CMS enforcement is capped at 40% of net income
A Deduction from Earnings Order cannot take more than 40% of the paying parent's net income. This is a collection cap, not a limit on the calculated liability.
Frequently asked