CMS Child Maintenance

The Child Maintenance Service has used a gross-income-based formula since 2012 (Child Support (Maintenance Calculations) Regulations 2012). The calculator first reduces the paying parent's gross weekly income for other relevant children living in their household — −11% for one, −14% for two, −16% for three or more — then applies the rate band that the reduced income falls into:

• Nil rate: gross weekly income under £7 — nothing is payable.
• Flat rate: £7 to £100/week — a flat £7/week.
• Reduced rate: £100.01 to £200/week — £7 plus a taper on income above £100: 17% (1 child), 25% (2) or 31% (3+).
• Basic rate: £200.01 to £800/week — 12% (1 child), 16% (2) or 19% (3+) of the whole income.
• Basic-plus: £800.01 to £3,000/week — the basic-rate percentage on the first £800 plus 9% / 12% / 15% on the slice above.
• Above £3,000/week: the CMS formula stops at £3,000; the receiving parent can apply to court for a "top-up" order on the excess.

Shared care then reduces the liability by 1/7 for each whole night per week the children average with the paying parent, up to 6/7 — the calculator rounds part-nights down, and keeps a £7/week minimum in the basic and basic-plus bands. From 3.5 nights a week (about 175 nights a year) the parents are treated as sharing care equally and no formula liability arises.

Assumptions and limits: the estimate uses the income figure you enter, whereas the CMS takes gross taxable income from HMRC records (after pension contributions) and can vary it for unearned income, assets or special expenses — none of which this tool models. It also does not apply the flat rate that covers paying parents on most benefits, handle different care arrangements for different children, or add the 4% collection fee the CMS charges when it collects and passes on payments rather than the parents paying directly.