How is child maintenance calculated?

Short answer

The Child Maintenance Service applies a percentage of the paying parent’s gross weekly income taken from HMRC records: 12% for one child, 16% for two, and 19% for three or more. Overnight stays and other children in the household reduce the figure.

The CMS does not weigh up what a child costs. It applies a formula to the paying parent's gross weekly income, drawn straight from HMRC data for the most recent tax year, and adjusts it for a handful of factors.

The basic calculation

12% of gross weekly income for one child, 16% for two, 19% for three or more.
Shared care reduces the figure by one seventh for each night a week, on average: 52 nights a year or fewer makes no difference; 53–103 nights cuts it by a seventh; 104–155 by two sevenths; 156–174 by three sevenths; and 175 or more nights takes it to a flat £7 a week.
Other children in the paying parent's household reduce the income before the percentage is applied.
Gross weekly income below £200 attracts a flat rate of £7 a week, and income between £200 and £800 may produce a reduced rate.
Income above £3,000 a week is outside the formula. The receiving parent can apply to the family court for a top-up order on the excess.

The government's calculator at gov.uk gives an estimate before you apply.

Getting paid, and enforcing it

Direct Pay is the default: the CMS calculates and notifies, and the paying parent pays the other directly. It is free. Collect and Pay is used where payments are unreliable or there is a history of abuse, and it costs both sides — the paying parent adds 20% on top and the receiving parent loses 4% of each payment. You can ask to switch if payments are missed, with evidence.

Enforcement powers are substantial: deduction from earnings, regular or lump sum deductions from a bank account, a charging order over property, disqualification from driving, removal of a passport, and in deliberate cases committal to prison for up to six weeks. Report missed payments straight away — the CMS aims to act after two consecutive missed payments.

A family-based arrangement avoids all of this. There is no fee, no formula and complete flexibility, including paying in kind. The trade-off is that it cannot be enforced, so if it breaks down either parent can apply to the CMS at any time. If income changes by 25% or more, either parent can ask for an interim review, and where you suspect undeclared or unearned income you can ask the CMS to consider a variation.

Read the full guide: Child Maintenance ServiceCovers eligibility, the process, deadlines, and next steps in depth.

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