How Is Child Maintenance Calculated in 2026?
A complete guide to the official CMS formula used to calculate child maintenance payments in the UK.
Quick Answer
Child maintenance is calculated as a percentage of the paying parent's gross weekly income:
- 12% for 1 child
- 16% for 2 children
- 19% for 3 or more children
This applies to the "Basic Rate" band (£200-£800/week income). Other factors like shared care and other children can reduce this amount.
The 4-Step CMS Calculation
The Child Maintenance Service (CMS) uses a standardised formula to calculate maintenance. Here's exactly how it works:
Calculate Weekly Income
Start with the paying parent's gross annual income (before tax). This includes salary, bonuses, and other taxable income.
Weekly Income = (Gross Annual Income - Pension Contributions) / 52
Pension contributions are deducted because the CMS uses income after pension deductions.
Determine Your Rate Band
Your weekly income determines which "rate band" applies:
| Rate Band | Weekly Income | How Much You Pay |
|---|---|---|
| Nil Rate | Under £7 | Nothing |
| Flat Rate | £7 - £100 | £7 per week |
| Reduced Rate | £100 - £199 | Sliding scale |
| Basic Rate | £200 - £800 | 12% / 16% / 19% |
| Basic Plus | Over £800 | Extra 9% / 12% / 15% on amount over £800 |
Most people fall into the Basic Rate band. £800/week = £41,600/year gross.
Adjust for Other Children
If you have other children living with you (not in this maintenance arrangement), your income is reduced before the percentage is applied:
- 1 other child: 11% reduction
- 2 other children: 14% reduction
- 3+ other children: 16% reduction
Apply Shared Care Deduction
If the child stays overnight with the paying parent regularly, the amount is reduced:
| Nights Per Year | Reduction |
|---|---|
| 0 - 51 nights | No reduction |
| 52 - 103 nights | 1/7 off (14%) |
| 104 - 155 nights | 2/7 off (29%) |
| 156 - 174 nights | 3/7 off (43%) |
| 175+ nights (50/50) | 50% off, minus £7 per child |
52 nights = 1 night per week average. 175 nights = roughly 50/50 shared care.
Example Calculation
Scenario: Parent earns £40,000/year, has 2 children in the arrangement, no other children, and has the children 52 nights per year.
- 1. Weekly income: £40,000 / 52 = £769.23
- 2. Rate band: Basic Rate (£200-£800)
- 3. Calculate: £769.23 x 16% = £123.08/week
- 4. Shared care (52 nights = 1/7 off): £123.08 - £17.58 = £105.50/week
Result: £105.50 per week (£457 per month)
Calculate Your Exact Amount
Our free calculator uses the official CMS formula to give you an accurate estimate.
Frequently Asked Questions
What income is used for child maintenance?
Gross income before tax, including salary, wages, bonuses, and other taxable income. Pension contributions are deducted. Benefits are not usually included unless you're on the Flat Rate.
How often is child maintenance reviewed?
The CMS reviews cases annually using HMRC data. You can also request a review if your income changes by 25% or more.
Can I make a private arrangement instead?
Yes, parents can agree their own "family-based arrangement" without using the CMS. This avoids the CMS collection fees. Our calculator can help you agree a fair amount.