Guide · Updated 07/07/2026
How child maintenance is calculated
The 2012 scheme uses a fixed formula set out in Schedule 1 to the Child Support Act 1991 and the Child Support Maintenance Calculation Regulations 2012. There is no discretion in the standard calculation: given the same inputs, everyone gets the same answer. That makes it checkable — and this page shows you how to check it.
The six steps
Find gross weekly income
Annual gross income — normally the latest HMRC tax-year figure — divided by 365, multiplied by 7. Gross means before tax and National Insurance but after pension contributions. See Income & HMRC.
Check which rate applies
Nil, flat, reduced, basic or basic plus, depending on the weekly figure and the paying parent's circumstances (see table below).
Reduce for relevant other children
If the paying parent or their partner receives Child Benefit for other children living with them, gross income is reduced by 11% (one child), 14% (two) or 16% (three or more) before the formula is applied.
Apply the percentage
For basic rate: 12% for one qualifying child, 16% for two, 19% for three or more — on income up to £800 a week. Income between £800.01 and £3,000 attracts the lower "basic plus" percentages: 9%, 12% and 15%.
Reduce for shared care
The figure is cut by 1/7 for each weekly-equivalent night band the child stays overnight with the paying parent. See shared care.
Apportion between receiving parents
If the paying parent pays for children in more than one household, the total is split in proportion to the number of qualifying children with each receiving parent.
The five rate bands
| Rate | Gross weekly income | What is payable |
|---|---|---|
| Nil | Below £7, or paying parent is (e.g.) a child under 16, a prisoner, or a 16–19-year-old in full-time non-advanced education | Nothing |
| Flat | £7 to £100, or paying parent receives a prescribed benefit (e.g. Universal Credit, State Pension, ESA, JSA) | £7 a week regardless of number of children |
| Reduced | £100.01 to £199.99 | £7 plus a percentage of income over £100: 17% (1 child), 25% (2), 31% (3+) |
| Basic | £200 to £800 | 12% (1 child), 16% (2), 19% (3+) of gross weekly income |
| Basic plus | £800.01 to £3,000 | Basic rate on the first £800, then 9% (1 child), 12% (2), 15% (3+) on the remainder |
The basic-plus split at £800 is frequently misunderstood — including in CMS phone explanations. A paying parent on £1,000 a week with one child pays 12% of £800 plus 9% of £200, not 12% of £1,000. If your decision letter shows a single percentage applied to income over £800, something is wrong.
Reductions before and after the percentages
Relevant other children (applied to income, before the formula)
| Other children in paying parent's household | Gross income reduced by |
|---|---|
| 1 | 11% |
| 2 | 14% |
| 3 or more | 16% |
Shared care (applied to the result, after the formula)
| Overnights per year | Band | Reduction |
|---|---|---|
| 52–103 | A | 1/7 |
| 104–155 | B | 2/7 |
| 156–174 | C | 3/7 |
| 175+ | D | 1/2, plus a further £7 a week per child in this band |
Shared care cannot reduce a basic or reduced rate liability below £7 a week. Flat-rate payers on benefits pay nothing if they have at least 52 overnights a year.
Worked examples
Example 1 — straightforward basic rate
Gross income £31,200 a year → £598.36 a week (×7 ÷ 365 basis). Two qualifying children, no other children, no shared care.
£598.36 × 16% = £95.74 a week.
Example 2 — basic plus, other child, shared care
Gross income £62,400 a year → £1,196.71 a week. One qualifying child; one other child in the paying parent's household; 110 overnights a year (Band B).
- Income after 11% other-child reduction: £1,196.71 × 0.89 = £1,065.07
- Basic: £800 × 12% = £96.00; Basic plus: £265.07 × 9% = £23.86 → £119.86
- Shared care Band B: £119.86 × 5/7 = £85.61 a week
Example 3 — reduced rate
Gross income £8,320 a year → £159.56 a week. One qualifying child, no adjustments.
£7 + (£59.56 × 17%) = £17.13 a week.
Run your own numbers through the official GOV.UK calculator, then compare against your decision letter line by line: income figure, tax year, pension deduction, other children, shared care band, apportionment. Any mismatch is a ground for mandatory reconsideration.
Default maintenance decisions
Where the CMS cannot get adequate income information it can impose a default rate: £39 a week for one child, £51 for two, £64 for three or more. Defaults are meant to be temporary and are replaced (and normally recalculated back to the effective date) once real figures arrive. If you are on a default because the CMS failed to process information you actually supplied, that is challengeable — and complainable.
The income cap and top-ups
The formula ignores gross income above £3,000 a week (£156,000 a year). Where the paying parent earns more, the receiving parent can apply to court for "top-up" maintenance under Schedule 1 to the Children Act 1989 — but only once a maximum CMS calculation is in place.
Sources
| Source | Type | Date | Credibility |
|---|---|---|---|
| Child Support Act 1991, Schedule 1 | Primary legislation | As amended | High — sets the rates |
| Child Support Maintenance Calculation Regulations 2012 (SI 2012/2677) | Primary legislation (SI) | As amended | High — the working rules |
| GOV.UK — How child maintenance is worked out | Official guidance | Current | High |
| Commons Library CBP-7770 — How is child maintenance calculated? | Parliamentary briefing | Oct 2025 | High — impartial, referenced |
| DWP online child maintenance calculator | Official tool | Current | High — indicative only |