Child maintenance (CMS) estimator
A neutral estimate of child maintenance under the Child Maintenance Service rules. The same weekly figure is what one parent pays and the other receives.
How the CMS calculation works
The Child Maintenance Service builds the figure in steps, and this tool follows the same order. It starts with the paying parent’s gross weekly income, ignoring anything above £3,000. The rate band is read off that income: a flat £7 up to £100, a reduced rate between £100 and £200, the basic rate of 12% to 19% between £200 and £800, and the basic-plus rate on income up to £3,000. If the paying parent has other children living with them, the income used for the basic rates is treated as 11% to 16% lower depending on how many, and the reduced rate uses a lower percentage table.
Shared care is the last step. The more nights the children stay with the paying parent, the larger the reduction, from one seventh up to a half plus an extra £7 a week per child once stays pass 175 nights a year. Both parents see the same number, because maintenance paid by one is maintenance received by the other.
Worked example
Take a gross weekly income of £500, one child, no other children at home, and 52 nights of shared care a year. That income sits in the basic band, so the rate is 12%, which is £60 a week. The 52 nights fall in the one-seventh band, cutting it to about £51 a week, roughly £223 a month. Raise the nights or add other children and the figure falls further.
Common questions
How is child maintenance calculated?
The Child Maintenance Service works from the paying parent’s gross weekly income. On the basic rate that is 12% for one child, 16% for two and 19% for three or more. Income is first reduced if the payer has other children living with them, and then again for nights the children stay overnight.
What are the basic and basic-plus rates?
The basic rate of 12%, 16% or 19% applies to gross weekly income between £200 and £800. Above £800 the basic-plus rate adds 9%, 12% or 15% on the slice up to £3,000. Income above £3,000 a week is not counted in the standard calculation.
How do overnight stays reduce the amount?
Nights the child spends with the paying parent cut the bill. Between 52 and 103 nights a year reduces it by one seventh, 104 to 155 by two sevenths, and 156 to 174 by three sevenths. At 175 nights or more it is halved and reduced by a further £7 a week for each child.
What if the payer has other children to support?
If the paying parent has other children living in their household, the basic and basic-plus rates are worked out on gross income treated as lower: 11% lower for one other child, 14% for two and 16% for three or more. On the reduced rate, for income between £100 and £200, the regulations use a lower percentage table instead. This tool applies both rules.
Is this the official figure?
No. This is an estimate to show how the rules fit together. The Child Maintenance Service uses your exact income from HMRC and can vary the amount for special circumstances, so treat the gov.uk calculator and any CMS decision as the authority.