Child Maintenance Calculator (UK)
Estimate how much child maintenance the Child Maintenance Service (CMS) would work out, from the paying parent's gross income, the number of children, shared-care nights and any other children in the household.
The Child Maintenance Service (CMS) applies a fixed statutory formula — the 2012 gross-income scheme — rather than judging what each parent "should" pay. The result turns on four things: the paying parent's gross weekly income, how many children they pay for, how many nights those children stay overnight, and whether the paying parent has other children living in their own household. This calculator reproduces that formula so you can see a close estimate before you ever contact the CMS; only the CMS's own assessment is legally binding.
How CMS child maintenance is worked out
The CMS runs the calculation in a set order. It starts from your gross income figure (which it pulls automatically from HMRC), reduces it if you support other children at home, drops it into a rate band, and finally applies a shared-care reduction for overnight stays.
Step 2 — apply the rate band to the adjusted income (see table)
Step 3 — take off the shared-care reduction: −1/7, −2/7, −3/7, or half, by nights per year
| Gross weekly income | Rate | 1 / 2 / 3+ children |
|---|---|---|
| Below £7 | Nil | £0 |
| £7–£100 (or on benefits) | Flat | £7 flat |
| £100.01–£199.99 | Reduced | £7 + 17% / 25% / 31% of income over £100 |
| £200–£800 | Basic | 12% / 16% / 19% |
| £800.01–£3,000 | Basic plus | +9% / 12% / 15% on the part over £800 |
Only income up to £3,000 a week gross (£156,000 a year) counts. Beyond that the CMS stops; a receiving parent who wants more can apply to court for a "top-up" order. Note that the percentages on the slice above £800 are deliberately lower than on the first £800 — a high earner's marginal rate falls, it doesn't rise.
What each input means
Gross weekly income is pay before Income Tax and National Insurance but after any occupational or personal pension contributions — pensions come off first. Children you pay for counts only the children of this particular case. Other children in your home covers biological, adopted or step-children you or your partner support; they reduce your assessable income before the rate is applied. Nights is the number of nights per year the qualifying children stay overnight with the paying parent — this is the single biggest lever most parents can evidence.
Shared care reduces the amount
| Nights per year with paying parent | Reduction |
|---|---|
| 52 to 103 | 1/7 off |
| 104 to 155 | 2/7 off |
| 156 to 174 | 3/7 off |
| 175 or more | Half off, then £7 less per child per week |
Where care is genuinely equal (175+ nights), the amount is halved and then reduced by a further £7 per child per week — which can bring a flat-rate or low-basic-rate case down to nil. If overnight stays can't be agreed, the CMS assumes the band that best fits the actual pattern.
Worked examples
1. Low income / flat rate. A paying parent earns £90 a week, or is on qualifying benefits. They fall in the £7–£100 flat band, so they pay £7 a week regardless of how many children — about £30 a month.
2. Standard / basic rate. A parent earns £550 a week gross, pays for 2 children, has no other children at home and no overnight stays. The basic rate for 2 children is 16%: 550 × 16% = £88 a week (about £381 a month). If the children stayed 60 nights a year, a 1/7 reduction brings it to about £75.43 a week.
3. High earner with shared care. A parent earns £1,200 a week gross and pays for 3 children who stay 110 nights a year. This is a basic-plus case: 800 × 19% + 400 × 15% = 152 + 60 = £212 a week before care. 110 nights is the 2/7 band, so 212 × 5⁄7 = £151.43 a week (about £656 a month).
Nuances, edge cases and special circumstances
The flat formula covers the common case, but several real-world situations change the result:
- Pension contributions are deducted from gross income before assessment, so paying more into a pension genuinely lowers a CMS liability — a legitimate planning point, though the CMS can challenge contributions it considers "diversion".
- Self-employment uses taxable profits from the latest HMRC self-assessment, not drawings. If profits swing year to year, the figure can lag reality by up to a tax year.
- Dividends, rental and investment income aren't in the standard gross-income figure. A receiving parent can apply for a variation to add "unearned income" of £2,500+ a year.
- Bonuses and overtime are already inside the annual HMRC figure, so a one-off bonus raises the assessed weekly income for that review year.
- Income above £3,000/week is ignored by the CMS; the extra is a court matter.
- Collect & Pay vs Direct Pay: if the CMS collects and passes on the money, it adds a 20% fee for the paying parent and takes 4% from the receiving parent. Direct Pay (parents arrange the transfer themselves) is free — this calculator shows the pre-fee assessment.
- Annual review: the CMS re-checks income every year against HMRC data, so payments can step up or down without either parent asking.
Benchmark payments by income
Weekly maintenance on the basic/basic-plus rate, no shared care and no other children in the household. Use it to sanity-check the calculator above.
| Gross weekly income | 1 child | 2 children | 3+ children |
|---|---|---|---|
| £200 | £24 | £32 | £38 |
| £300 | £36 | £48 | £57 |
| £400 | £48 | £64 | £76 |
| £500 | £60 | £80 | £95 |
| £600 | £72 | £96 | £114 |
| £800 | £96 | £128 | £152 |
| £1,000 | £114 | £152 | £182 |
| £1,500 | £159 | £212 | £257 |
Frequently asked questions
How much is child maintenance for 1 child in the UK?
Is child maintenance based on gross or net income?
Does shared care reduce child maintenance payments?
How does the CMS treat self-employment income?
Do pension contributions reduce child maintenance?
Is this the official CMS amount?
Sources & editorial note
The formula, rate bands and shared-care reductions follow the UK government's Child Maintenance Service guidance, "How child maintenance is worked out" on GOV.UK, under the 2012 gross-income scheme. Rate figures are those current for the 2026 tax year and are maintained centrally; the CMS's own calculator and caseworker assessment remain the definitive source.