How Is Child Maintenance Calculated by the CMS?
A full breakdown of how the CMS works out how much child maintenance should be paid, including all income bands and rates.
The basics: gross income is used
The CMS calculates child maintenance based on the paying parent's gross annual income - that is, income before income tax and National Insurance are deducted. The CMS gets this figure directly from HMRC, so it reflects your actual earnings.
This is why many paying parents feel the CMS calculation seems high - because it's based on your gross pay, not your take-home pay. Our net pay calculator can show you what the payments would look like based on what you actually take home each month.
The five rate bands
The CMS uses five different rate bands depending on the paying parent's gross weekly income:
1. Nil Rate (£0–£7 per week gross)
No child maintenance is payable. This also applies if the paying parent is on certain benefits or in prison.
2. Flat Rate (£7–£100 per week gross)
A fixed amount of £7 per week is payable regardless of how many children are involved.
3. Reduced Rate (£100.01–£200 per week gross)
The amount is calculated using a formula:
| Number of children | Formula |
|---|---|
| 1 child | £7 + 17% of income above £100 |
| 2 children | £7 + 25% of income above £100 |
| 3+ children | £7 + 31% of income above £100 |
4. Basic Rate (£200.01–£3,000 per week gross)
This is the most common band. The paying parent pays a percentage of their gross weekly income:
| Number of children | % of gross weekly income |
|---|---|
| 1 child | 12% |
| 2 children | 16% |
| 3+ children | 19% |
5. Basic Rate Plus (over £3,000 per week gross)
For higher earners, the paying parent pays the basic rate on the first £3,000 of weekly gross income, plus a reduced rate on income above that.
How much child maintenance for 1 child?
For one child at the basic rate, you pay 12% of gross weekly income. So if you earn £500/week gross, that's £60/week (£260/month). Use our calculator to work this out from your take-home pay.
How much child maintenance for 2 children?
For two children, the rate is 16% of gross weekly income. On £500/week gross, that's £80/week (£347/month).
How does shared care affect the amount?
If the paying parent has the children to stay overnight, the CMS will reduce the maintenance amount. See our full guide: How shared care affects child maintenance.
Frequently Asked Questions
Does the CMS use my current salary or last year's?
What if I have children with more than one person?
Can the CMS look at my partner's income?
Want to know exactly what you'd pay?
Use our free net pay calculator - enter your take-home pay, not gross, for a realistic figure.
Try the Calculator →