Child Maintenance (CMS) Estimate Calculator

How to do it

1. 1
   Enter the gross weekly income

   Use the paying parent's income before tax.

2. 2
   Enter the number of children

   Include those the maintenance is for.

3. 3
   Enter nights of care

   Add the nights per year the children stay with the paying parent.

4. 4
   Add other children

   Enter children living with the paying parent who are not part of the claim.

5. 5
   Read the estimate

   See the weekly, monthly and yearly amounts.

About this tool

The Child Maintenance Service works out maintenance as a percentage of the paying parent's gross weekly income, depending on the number of children, with reductions for other children in the paying parent's household and for nights the children spend with the paying parent. This calculator applies the basic rule of thumb, including the flat and reduced rates for low incomes, and shows the weekly and monthly amounts. All percentages and thresholds are in editable tables, since the service can change them and applies details that this tool simplifies.

Who this is for Separated parents who want an idea of what maintenance might be before they use the government service or agree a family-based arrangement, and advisers who need a quick check.

The basic rate For income up to £800 a week the basic rate is 12 percent for one child, 16 percent for two and 19 percent for three or more. For the part of income between £800 and £3,000 a week, the percentages are lower: 9, 12 and 15 percent. Income above £3,000 a week is not counted in the basic calculation. The figure uses gross weekly income as shown by HMRC data.

Lower incomes Below £7 a week the amount is nil. For income between £7 and £100 a week a flat rate of £8 applies. Between £100 and £200 a week a reduced rate applies, which the tool approximates with the flat rate plus a share of the income above £100. The service applies more detailed rules for these cases.

Other children and shared care If the paying parent has other children living with them, a share of their income is disregarded: 11 percent for one other child, 14 percent for two and 16 percent for three or more. For shared care, the amount is reduced by one seventh if the children stay for 52 to 103 nights a year, two sevenths for 104 to 155 nights, three sevenths for 156 to 174 nights and by one half if 175 nights or more, together with a further £7 a week per child in that last case.

Worked example A parent with a gross income of £650 a week and two children pays 16 percent, £104 a week. With 52 nights of care a year, the amount is reduced by one seventh, to about £89.14 a week, or about £386 a month. With £1,000 a week and one child the basic amount is 12 percent of £800 plus 9 percent of £200, £114 a week.

Limits This is an estimate, and the service uses detailed rules and income data. Voluntary family-based arrangements can be different. This is not legal advice.

Worked example

A parent with £650 gross a week and two children pays 16 percent, £104 a week, reduced to about £89 with 52 nights a year of shared care.