The Child Maintenance Service (CMS) generally calculates maintenance using the paying parent's relevant taxable gross income, rather than the net amount received after Income Tax and National Insurance. Eligible pension contributions can reduce the relevant income. CMS usually obtains historic annual income from HMRC and converts it into a weekly figure before applying the appropriate maintenance rules.
Is Child Maintenance Calculated on Gross or Net Income?
Under the current statutory Child Maintenance Service calculation, the paying parent's relevant gross income is normally used to establish how much child maintenance is payable. This means the starting figure is generally before Income Tax and National Insurance are deducted.
CMS also accounts for eligible occupational and personal pension contributions. The figure used for maintenance can therefore be different from both the headline salary in an employment contract and the amount received in a bank account.
Income is only one part of the assessment. CMS also considers the applicable rate, the number of qualifying children, certain other supported children and overnight shared care.
Our UK Child Maintenance Calculator homepage explains how to estimate payments. You can also use the free child maintenance calculator for supported income and family circumstances.
Key point: Gross income for CMS purposes does not always equal the undeducted headline salary. Eligible pension contributions and statutory income adjustments may already be reflected.
What Is the Difference Between Gross Salary and Net Salary?
Gross salary is the amount earned before Income Tax and National Insurance have been taken away. Net salary, often called take-home pay, is the amount received after payroll deductions have been made.
Those deductions may include Income Tax, National Insurance and employee pension contributions. Other deductions can also affect the amount paid into a bank account.
Usually the relevant starting point for the CMS income calculation, subject to eligible adjustments.
The amount received after payroll deductions. It is not generally the starting income used to apply CMS maintenance percentages.
Why Does the Difference Matter?
Calculating 12%, 16% or 19% from take-home pay can substantially underestimate a maintenance amount in an ordinary Basic-rate case.
A paying parent should therefore check the relevant income basis rather than simply entering the amount their employer transfers into their bank account.
Are Income Tax and National Insurance Deducted Before CMS Calculates Maintenance?
No. Under the current CMS scheme, relevant gross income is ordinarily considered before Income Tax and National Insurance are removed.
That differs from a calculation based on net earnings. CMS does not normally take the amount left after these deductions and then apply the Basic-rate percentage.
Example: Gross and Net Pay
Illustrative gross weekly income: £600
Illustrative take-home pay: £480
Qualifying children: 1
Ordinary Basic rate: 12%
Relevant calculation: £600 × 12%
The £480 take-home figure is purely illustrative and is not intended as an Income Tax calculation. The example assumes £600 is the appropriate CMS income figure and there are no other adjustments or variations.
A 12% calculation based on £480 would produce £57.60, rather than the illustrative £72 based on £600. Using the wrong income figure can make a maintenance estimate inaccurate.
Where Does CMS Get Your Income Information?
CMS usually obtains the paying parent's historic annual income from HM Revenue & Customs (HMRC). This information may have been supplied by an employer, the paying parent or another party such as an accountant.
The income information normally comes from the latest available complete tax year. In the UK, a tax year runs from 6 April to 5 April.
The CMS decision normally identifies which tax year was used in establishing the gross annual income.
Why Might CMS Use an Older Salary?
Your current salary may differ from the earnings reported to HMRC during the latest available complete tax year. This can happen after a promotion, job change, reduced working hours or a period of unemployment.
CMS has current-income rules for certain situations, but a difference in current earnings does not automatically change every assessment.
Practical check: Compare the gross annual income shown in the CMS decision with the relevant HMRC tax-year information. Contact CMS if you believe the figure is incorrect.
How Does CMS Convert Annual Gross Income into Weekly Income?
CMS converts the relevant annual income amount into a weekly figure. The standard conversion uses an annual amount divided by 365 and multiplied by seven.
Example: £36,500 Annual Income
Relevant annual gross income: £36,500
Weekly conversion: £36,500 × 7 ÷ 365 = £700
CMS then considers the appropriate maintenance rates and other factors affecting the assessment.
This conversion should not be confused with dividing an annual salary by exactly 52 weeks. Differences can arise when comparing estimates.
Gross Salary Child Maintenance Calculation Examples
The following examples show ordinary Basic-rate maintenance for different relevant gross weekly incomes. They assume no qualifying shared care, other supported children, additional pension adjustment or variation.
| Relevant Weekly Income | 1 Child (12%) | 2 Children (16%) | 3+ Children (19%) |
|---|---|---|---|
| £250 | £30.00 | £40.00 | £47.50 |
| £400 | £48.00 | £64.00 | £76.00 |
| £500 | £60.00 | £80.00 | £95.00 |
| £600 | £72.00 | £96.00 | £114.00 |
| £700 | £84.00 | £112.00 | £133.00 |
| £800 | £96.00 | £128.00 | £152.00 |
Example: Two Children on £36,500 Annually
Relevant gross annual income: £36,500
Weekly equivalent: £700
Two-child Basic rate: 16%
£700 × 16% = £112
What If Gross Weekly Income Is Above £800?
For a straightforward Basic Plus case, CMS applies one percentage to the first £800 and a lower percentage to income above £800, up to the normal £3,000 weekly ceiling.
| Children | First £800 | Income Above £800 |
|---|---|---|
| 1 child | 12% | 9% |
| 2 children | 16% | 12% |
| 3 or more | 19% | 15% |
Example: £1,000 Weekly Income, Two Children
First £800 × 16% = £128
Additional £200 × 12% = £24
Combined weekly amount: £128 + £24
For lower-income bands and special circumstances, visit our Child Maintenance Rates guide.
Do Overtime, Bonuses and Commission Count Towards Child Maintenance?
Taxable payments such as overtime, bonuses and commission can be relevant to the CMS income figure. Where these payments form part of the income information reported to HMRC for the relevant tax year, they may affect the historic income used for assessment.
The specific treatment depends on the income category, evidence and whether CMS is using historic or current-income information.
Overtime Pay
Overtime earnings can form part of taxable employment income. Occasional overtime may therefore influence historic income when it is included in the relevant tax-year records.
Annual Bonuses
A taxable bonus received during the relevant year can also affect income reported to HMRC. However, a bonus does not necessarily mean the parent will receive the same amount every year.
Commission
Commission-based earnings may fluctuate throughout the year. CMS looks at the appropriate income evidence rather than assuming every month will produce the same commission.
Example: Basic Salary Plus Bonus
Illustrative taxable base earnings: £30,000
Taxable bonus: £6,500
Combined annual income: £36,500
Weekly equivalent: £700
One-child Basic rate: 12%
This assumes the total is the relevant CMS income figure before additional adjustments. It is not a forecast of the parent's future earnings.
Are Pension Contributions Deducted from Gross Income for CMS?
Eligible occupational and personal pension contributions can reduce the income used in a child maintenance assessment. Workplace pension contributions may already be reflected in the taxable income reported to HMRC.
Qualifying payments made directly to a private pension provider may need to be considered separately. Relevant pension tax relief can also affect the amount of the eligible deduction.
Example: Eligible Additional Pension Contribution
Starting relevant weekly income: £600
Additional eligible gross pension contribution: £50
Adjusted relevant income: £550
One-child Basic rate: 12%
If a contribution is already reflected in the CMS income figure, deducting it again would produce an incorrect estimate. Check the scheme and income information used.
Read our detailed Child Maintenance and Pensions guide for workplace pensions, personal pensions and tax relief.
Is Self-Employed Child Maintenance Based on Gross Turnover or Profit?
For self-employed parents, CMS generally uses relevant taxable business profits rather than the total sales or turnover generated by the business.
For example, a sole trader with £60,000 annual turnover and £25,000 of eligible business expenses may have taxable profit of £35,000, assuming those are the complete relevant figures.
The correct amount depends on the information supplied to HMRC and the applicable rules. Company directors and individuals receiving dividends may have more complicated income arrangements.
Business revenue before eligible costs. It is not automatically the CMS assessable income.
The profit figure calculated under applicable tax rules, generally used as the starting point for self-employment income.
For more detail, visit Child Maintenance for Self-Employed Parents .
Does CMS Include Dividends, Rental Income and Pension Income?
Other income sources may be relevant, but they are not all treated identically under the ordinary CMS calculation.
Taxable Pension Income
Relevant taxable occupational and personal pension income may be included in the paying parent's income. This is different from eligible pension contributions, which can reduce income.
Dividends and Investment Income
Some dividend and investment income may be considered through an additional-income variation. The applicable evidence and statutory threshold must be satisfied.
Rental Income
Qualifying rental income can also be considered through a CMS variation. Parents should not automatically add gross rental receipts to employment salary without applying the correct rules.
| Income Source | General Treatment |
|---|---|
| Employment salary | Relevant taxable earnings |
| Self-employment | Relevant taxable profits |
| Occupational or personal pension income | Can count as relevant income |
| Dividends and investment interest | May be considered through a variation |
| Rental income | May be considered through a variation |
| Other qualifying assets or diverted income | Special variation rules may apply |
CMS determines whether additional income or a special variation should affect the official maintenance assessment.
GOV.UK — Additional Income and Expenses →Does the Receiving Parent's Income Affect Child Maintenance?
The standard CMS formula generally uses the paying parent's relevant income. It does not add together both parents' salaries and calculate maintenance using their combined income.
This means the receiving parent's salary does not ordinarily change the standard statutory rate applied to the paying parent's income.
Parents may nevertheless agree their own private maintenance arrangement based on their wider family circumstances.
Important: Private agreements and official CMS assessments are different. The ordinary statutory formula focuses on the paying parent's relevant income and other recognised factors.
What Happens If Your Gross Income Changes?
Gross earnings can change after CMS has made a maintenance decision. A parent may start another job, receive a promotion, reduce their working hours or become unemployed.
CMS normally conducts an annual review, but some qualifying changes can be considered earlier.
The 25% Current-Income Rule
Under the general current-income rule, CMS may use updated income evidence where current income is at least 25% higher or lower than the relevant historic income, subject to the statutory requirements.
Illustrative Income Change
Historic gross weekly income: £600
New gross weekly income: £420
Income difference: £180
Percentage fall: 30%
In this example, the income difference meets the general 25% numerical threshold. CMS would still need suitable evidence and confirmation that the applicable conditions are met.
A change of less than 25% does not automatically trigger a revised current-income assessment, although other rules and changes can still be relevant.
A change in salary does not authorise a paying parent to change an existing official payment plan independently. Report changes as required and follow CMS instructions.
Why Does an Employer Use Net Earnings for Child Maintenance Deductions?
Employers sometimes receive a Deduction from Earnings Order (DEO) requiring them to deduct maintenance from a paying parent's earnings.
Under employer deduction rules, the amount available for deduction is based on defined net earnings after applicable deductions such as Income Tax, Class 1 National Insurance and pension contributions.
This is a separate issue from calculating the original maintenance liability, which ordinarily begins with relevant gross income.
Used to determine the statutory weekly maintenance liability under the applicable CMS rules.
Used to determine the amount that can be deducted through an employer's DEO.
Confusing these two processes can lead to the mistaken belief that CMS always calculates maintenance using take-home salary.
GOV.UK — Employer Deduction Rules →Common Mistakes When Calculating Child Maintenance from Salary
Income figures can look similar on a payslip, P60 or tax return, but they may not represent the same amount for CMS purposes.
- Using take-home pay instead of the relevant gross income figure.
- Deducting Income Tax or National Insurance before applying CMS rates.
- Deducting pension contributions that were already reflected in HMRC income.
- Ignoring taxable overtime, commission or bonus earnings.
- Using business turnover rather than relevant taxable self-employment profits.
- Treating dividends and rental income exactly like ordinary employment earnings in every case.
- Assuming current monthly earnings automatically replace HMRC historic income.
- Confusing a Deduction from Earnings Order with the original CMS assessment.
How to Estimate Child Maintenance Using the Correct Income Figure
To create a more meaningful estimate, gather the appropriate income records before calculating maintenance.
Use the appropriate taxable employment, self-employment or pension income figure.
Confirm whether eligible pension contributions are already included in the income figure.
CMS can make an appropriate adjustment for eligible children supported elsewhere.
The appropriate income band determines the applicable maintenance calculation method.
Eligible overnight stays may reduce the weekly liability.
The final CMS result can depend on verified income, variations and other circumstances.
Visit our Child Maintenance Calculator UK homepage, or use the free child maintenance calculator to estimate a payment for supported circumstances.
Open Free Child Maintenance Calculator →Calculator limitation: Check whether the calculator expects gross income before or after eligible pension contributions. Do not subtract the same contribution twice. Complex income cases may require an official CMS decision.
Official GOV.UK Sources and Important Information
This guide discusses the statutory child maintenance framework used in England, Wales and Scotland. Northern Ireland has a separately administered Child Maintenance Service.
For official income assessments, variations or payment changes, use the appropriate government resources.
- GOV.UK — Detailed CMS Calculation Guide
- GOV.UK — How Child Maintenance Is Worked Out
- GOV.UK — CMS Annual Review Guide
- GOV.UK — Additional Income and Expenses
- GOV.UK — Deduction from Earnings Orders
- GOV.UK — Official Child Maintenance Calculator
Independent Website Disclaimer: Child Maintenance Calculator UK is an independent information website and is not affiliated with GOV.UK, DWP, HMRC or CMS. The examples are illustrative and do not replace an official CMS assessment or personalised advice.
Learn more about our Calculation Methodology , Editorial Policy and Disclaimer .