CMS Calculator (Child Maintenance Service)
Assess your 2012 CMS statutory maintenance liability after accounting for pension contributions, gross income, and shared care bands.
Calculate Child Maintenance Service (CMS) assessments with statutory income tiers, pension deductions, and shared care bands.
See also: Child Maintenance Calculator, NHS Take-Home Pay Calculator, VAT Calculator (UK)
How it is calculated
Assessable Income = Gross Taxable Pay − Pension; Band calculation applied then adjusted for overnight shared care.
Worked example: CMS Assessment on £40,000 Salary with 5% Pension
£40,000 gross salary, £2,000 pension contribution, 2 children, 52-103 nights shared care.
- Deduct pension: £40,000 − £2,000 = £38,000 net assessable income.
- Convert to weekly income: £38,000 ÷ 52 = £730.77 per week.
- Apply 2-child Basic Rate (16%): £730.77 × 16% = £116.92 base weekly liability.
- Apply 1/7th shared care reduction: £116.92 ÷ 7 = £16.70 discount.
- Net payable: £116.92 − £16.70 = £100.22 per week.
Weekly CMS liability is £100.22 (£434.29 monthly).
How to Use This Calculator (Step-by-Step)
- Input total gross pay from your P60, payslips, or self-assessment tax return.
- Enter all pension payments made during the tax year (HMRC automatically deducts allowable contributions).
- Select qualifying children count and overnight care arrangements.
- Check the weekly obligation to prepare your monthly household budget.
Frequently asked questions
Can the receiving parent request a review if circumstances change?
Yes. Either parent can request an annual CMS review, or an immediate change review if income shifts by 25% or more.
What income figure should I enter?
Enter total gross pay from your P60, payslips, or self-assessment tax return, as the how-to steps direct. Pension contributions for the tax year are entered separately, because they reduce the assessable income.
How do pension contributions affect the assessment?
Pension contributions reduce assessable gross income pound-for-pound, lowering the maintenance calculation legally. In the worked example, deducting 2,000 pounds of pension from a 40,000 pound salary leaves 38,000 pounds of assessable income.
How is a weekly figure turned into a monthly payment?
Multiply the weekly liability by 52 weeks and divide by 12 months. In the worked example, 100.22 pounds per week becomes 434.29 pounds per month by exactly that conversion.
What shared care bands are available?
Under 52 nights a year gives no deduction, 52 to 103 nights gives a one-seventh deduction, 104 to 155 nights two-sevenths, and 156 to 174 nights three-sevenths. Select the band matching the actual overnight pattern.
Which rate applies for two children?
In the worked example, two children use the 16% Basic Rate applied to weekly assessable income. The example applies 16% to 730.77 pounds per week to reach a 116.92 pound base weekly liability before the shared care reduction.