UK Child Maintenance Service (CMS) Calculator

By Bilal Butt, founder. Last verified: October 2026.

The CMS calculation uses only the paying parent's gross weekly income. The receiving parent's income is not in the formula.

Rates

Reduced rate, no other children: £7 + 17% (1 child) / 25% (2) / 31% (3+) of income over £100. With other children, the reduced-rate percentages are 14.1% / 13.2% / 12.4% (1 qualifying child, 1/2/3+ others), 21.2% / 19.9% / 18.9% (2 qualifying), 26.4% / 24.9% / 23.8% (3+ qualifying), applied to income over £100 plus £7.

Other children, default rate, cap, fees

For Basic/Basic Plus incomes (£200+), gross weekly income is first reduced by 11% (1 other child), 14% (2) or 16% (3+) — “other children” means children the paying parent or their partner gets Child Benefit for. The default rate is £39/week (1 child), £51 (2), £64 (3+) where income cannot be established. The cap is £3,000 gross/week under the 2012 CMS scheme; income above it is ignored by CMS, and the receiving parent may apply to court for a top-up. Collect and Pay fees are 20% added for the paying parent and 4% deducted for the receiving parent; Direct Pay has no collection fee. An outdated lower default figure that still appears on one summary page is not used here.

Shared care (per child)

Reduction after dividing the amount by the number of qualifying children: 52–103 nights = −1/7; 104–155 = −2/7; 156–174 = −3/7; 175+ = −50% plus a further £7/week per child reduction. After shared care the payment cannot fall below £7/week, except the flat-rate-on-benefits case: if the flat rate is due to benefits and there are 52+ nights, payment becomes £0 for that child. If the flat rate is due to income of £100 or less, shared care is ignored. Where parents agree at least 52 nights but not the exact number, CMS assumes 52 nights. Equal day-to-day care means £0 for that child.

No add-on percentage

There is no childcare/health/education percentage on top of the CMS amount. Instead, variations can increase assessable income (for example rental income over £2,500/year, or assets over £31,250) or reduce it for special expenses (normally each over £10/week, except disability costs), such as contact costs or boarding-school fee elements. Income over £3,000/week goes to court for a top-up.

Worked example

Gross weekly income £600, 2 children, 104 shared-care nights, no other children, no pension adjustment. Basic rate, 2 children = 16%. Before shared care: 16% × £600 = £96.00/week. 104 nights is in the 104–155 band, so reduce by 2/7: £96 × 5/7 = £68.57/week (£297.14/month; £3,565.71/year). The £7 floor is not triggered.

End of support

Age 16, or up to 20 if the child stays in approved full-time non-advanced education or training (over 12 hours/week supervised study, accepted before turning 19). Payments stop after the 20th birthday. University/advanced courses do not qualify. Northern Ireland runs a separate service.

Sources: GOV.UK, “How we work out child maintenance” (step-by-step guide); Child Support Maintenance Calculation Regulations 2012, reg. 49 (default £39/£51/£64); DWP leaflet and House of Commons Library (Collect and Pay 20%/4%). GOV.UK guide · 2012 Regulations

How to use this calculator

Enter the paying parent's gross weekly income after pension contributions and before tax and National Insurance. The receiving parent's income is not in the formula. Enter qualifying children (children the paying parent pays maintenance for), other children the paying parent supports and receives Child Benefit for, and shared-care nights per year with the paying parent. Tick the benefits box only if the paying parent (or their partner) receives a listed benefit — the flat £7 rate then applies instead of the percentage rates, with a special £0 result for that child at 52 or more shared-care nights.

Additional worked examples

The shared-care example shows why the reduction is applied per child, not to the total: each child's amount is reduced by the nights band, then the amounts are added back together. After shared care the payment cannot fall below £7/week, except in the benefits flat-rate case described above.

Common mistakes

• Using net pay. CMS uses gross weekly income after pension contributions, before tax and National Insurance.
• Using the receiving parent's income. It is not in the CMS formula at all.
• Using the old £38 default rate. The default rate is £39/week for one child (£51 for two, £64 for three or more). The £38 figure on a GOV.UK summary page is outdated and is not used here.
• Counting income above £3,000/week. CMS ignores income above £3,000/week under the 2012 scheme; a court top-up may be sought separately.
• Applying Collect and Pay fees to the wrong side. Collect and Pay charges 20% to the paying parent and 4% to the receiving parent; Direct Pay has no fee.

How courts deviate from the guideline

A guideline figure is a presumption, not a guarantee. Courts commonly depart where the guideline would be unjust or inappropriate on the facts: a child's proven needs or special expenses, a parent's other obligations, hardship, high or very low income, shared-care arrangements that change real costs, and tax or benefit effects the formula does not capture. Where a court deviates, it generally must explain why and state the guideline figure it departed from. That is why every calculator on this site shows its formula and its cap: you can see what the court starts from, even if the final order differs.

CMS is an administrative calculation, not a court guideline, so “deviation” works differently: the main routes outside the formula are a court top-up for high income above the cap, a variation for special expenses or income not captured by the calculation, and a private arrangement or family-based arrangement instead of CMS. A CMS calculation can be challenged if the income figure or the care pattern is wrong — check the inputs first.

When to hire a lawyer

An estimate is a starting point, not a strategy. Talk to a licensed attorney in the relevant jurisdiction before you rely on a figure if any of these apply: custody is disputed; there is a business, professional practice or complex property to value; retirement accounts, stock or deferred compensation are involved; either parent's income is disputed, imputed or largely non-cash; a child has special needs or disability; support is above a statutory cap; or the other party already has a lawyer. A lawyer can also advise on deviation factors, add-ons and enforcement in that jurisdiction — none of which a guideline calculator can decide. This site cannot recommend a specific lawyer and does not take referral fees.

Frequently asked questions

These questions are shown on the page in full. They are not marked up as FAQ structured data.

What is the UK CMS default rate?

£39 a week for 1 child, £51 for 2, £64 for 3 or more (weekly totals, not per child), where income cannot be established.

What is the CMS income cap?

£3,000 gross a week under the 2012 CMS scheme. Income above it is ignored by CMS; a court top-up may be sought.

How does shared care reduce CMS?

Per child: 52–103 nights −1/7, 104–155 −2/7, 156–174 −3/7, 175+ −50% plus a further £7 a week per child, subject to the £7 floor.

What if the paying parent earns over £3,000 a week?

CMS calculates only up to £3,000/week. For income above that, a court top-up application may be possible; this calculator does not estimate a top-up amount.

Do shared-care nights reduce the flat £7 rate?

At the flat rate, shared care is generally ignored — except that on benefits with 52 or more shared-care nights the result for that child is £0, as stated on this page.

Change log

Related

Other pages for the same jurisdiction or the same topic:

• Child Support Calculators & Guides by Jurisdiction