How child maintenance is calculated
When parents separate, the parent the child doesn't mainly live with usually pays child maintenance. The Child Maintenance Service (CMS) uses a set formula based on the paying parent's gross income, the number of children, and how often the child stays over. Here's how it works.
Basic rate percentages
For gross weekly income between £200 and £800, the CMS basic rate is a percentage of income:
- 1 child: 12%
- 2 children: 16%
- 3 or more: 19%
Income between £800 and £3,000 a week is charged at lower "basic plus" rates (9% / 12% / 15%) on the portion above £800. Income over £3,000 a week is outside the CMS, and the receiving parent can apply to court for a "top-up".
Flat and reduced rates
Below £200 a week, different rules apply: a reduced rate between £100 and £200, and a flat rate of £7 a week for income of £100 or less or for those on certain benefits.
Nights reduce the bill
If the child stays overnight with the paying parent, maintenance is reduced on a sliding scale:
- 52–103 nights a year: reduced by 1/7.
- 104–155 nights: reduced by 2/7.
- 156–174 nights: reduced by 3/7.
- 175+ nights: reduced by half, plus a further small reduction.
Other children count too
Two children, £600 a week, no shared care
A paying parent earning £600 gross a week with two children and no overnight stays falls in the basic rate band. The calculation is £600 × 16% = £96 a week, or about £416 a month. If the children stayed 60 nights a year, the 1/7 reduction would bring it to about £82.29 a week.
Common child maintenance mistakes
- Forgetting pension contributions reduce income. The CMS uses gross income after pension contributions, which can lower the figure.
- Ignoring shared-care nights. Overnight stays meaningfully reduce maintenance — keep an accurate record.
- Assuming the CMS is free. If the CMS collects and passes on payments, both parents pay collection fees; a direct arrangement avoids them.
- Overlooking the £3,000 cap. Very high earners are only assessed up to £3,000/week by the CMS; the rest needs a court top-up.