Important
This guide is mainly based on the statutory scheme for England, Scotland and Wales. Northern Ireland has its own CMS administration, although its calculation system follows the same broad six-step structure.
This is general information and signposting, not legal advice. Always check the decision notice, current GOV.UK guidance and the legislation that applied on the date of the decision.
Why Calculation Accuracy Matters
Incorrect Assessments
Wrong income, dates or household information can change the amount payable.
Underpayments & Overpayments
An error can affect either parent and may continue until corrected.
Incorrect Arrears
If liability or payment records are wrong, the arrears balance may also be wrong.
Enforcement
Unresolved debt can lead to collection and enforcement action.
Appeals
Certain calculation decisions can be challenged by mandatory reconsideration and tribunal appeal.
Complaints
Service failures and maladministration can be raised separately through complaint procedures.
Legal Framework
Child Maintenance and Other Payments Act 2008
Reformed the statutory child-maintenance system.
Read ActCalculation Regulations 2012
Contains detailed rules for historic/current income, pensions, rates, shared care, variations and decision making.
Read regulationsChild Support Information Regulations 2008
Contains rules governing information and evidence used for child support purposes.
Read regulationsData Protection Act 2018
Part of the legal framework governing personal data held and processed by public authorities.
Read ActCMS Decision Makers' Guide
DWP's published guidance for decision makers on child-maintenance decisions.
Open guidanceThe Six-Step Calculation
Work Out Gross Annual Income
CMS normally gets the paying parent's yearly gross income from HMRC and checks benefit information.
Adjust the Income Figure
CMS considers qualifying pension contributions, relevant other children, foreign exchange costs and any agreed variation affecting the income figure.
Apply the Correct Rate
The nil, flat, reduced, basic, basic-plus or default rules are applied according to the statutory circumstances.
Take Account of Children
CMS considers the number of qualifying children and relevant arrangements for other children supported by the paying parent.
Calculate the Weekly Amount
The appropriate percentages or statutory formula are applied.
Apply Shared-Care Reduction
Where applicable, the amount is reduced according to the average number of qualifying overnight stays.
What Income Does CMS Use?
Historic Income
CMS normally starts with the HMRC figure from the latest available tax year under the statutory rules. This is converted to a weekly amount.
Current Income
In circumstances allowed by the Regulations, CMS may use current income instead. The 2012 Regulations contain the rules for when current income can replace historic income.
Employment
Taxable earnings reported through HMRC can form part of the gross-income figure.
Self-Employment
HMRC tax information is normally central to the calculation, with separate current-income rules where applicable.
Pension Income
Taxable pension income can form part of the income assessment.
Unearned Income
Rental income, dividends and interest may be considered through a variation where the statutory conditions and thresholds are met.
Assets
Notional income can be considered through the statutory assets variation where qualifying assets meet the prescribed threshold.
Diversion
A variation may be available where income is being diverted to another person or purpose so that it is not reflected in the standard calculation.
Historic Income, Current Income & the 25% Rule
The current-income rules are technical. Regulation 23 contains a 25% tolerance for changes outside the annual-review or periodic current-income-check process. Whether a current figure should replace historic income depends on the statutory conditions and the facts of the case.
Pension Contributions — Official Rule
There is no official “12% safe limit”
DWP's current calculation guide states that qualifying pension contributions reduce the income figure used for child maintenance. Employer/occupational pension deductions are normally already reflected in the taxable income data received from HMRC. Direct private-pension contributions should be reported to CMS where appropriate.
Employer Pension
Where deductions have already reduced taxable pay, DWP guidance says they are normally already reflected in HMRC income information.
Private Pension Paid Directly
DWP guidance says CMS will usually reduce the income figure by the full qualifying contribution, including applicable tax relief.
Calculation Formula — Detailed Guide
A practical breakdown of the formula, percentages, pension treatment, shared care, other children, variations, travel expenses and higher-income cases.
Official DWP Calculation Formula
CMS normally starts with the paying parent's gross income before Income Tax and National Insurance, using HMRC information. It then applies permitted adjustments such as qualifying pension contributions, other children supported by the paying parent, certain foreign-exchange costs and any agreed variation before the statutory maintenance rates are applied.
Gross Income
Before Income Tax and National Insurance.
CMS normally uses the gross annual income figure supplied by HMRC and converts it to a weekly figure after applying the adjustments required at Step 2.
After Pension Contributions
Qualifying pension contributions can reduce the income figure used for child maintenance. Employer pension deductions may already be reflected in HMRC taxable income, while qualifying private pension contributions paid directly may need to be reported to CMS.
Pension Contributions — Practical Rule of Thumb
This is not an official CMS percentage threshold. Some parents use around 12% of gross income as a practical benchmark when considering whether pension contributions may attract closer scrutiny. The current DWP guidance does not create a 12% “safe limit”.
Very large or unusual contributions may become relevant where the facts suggest income is being diverted or manipulated so that it is not properly reflected in the maintenance calculation. CMS must still rely on the statutory variation rules and evidence rather than a general percentage rule.
Example — 10% Pension Contribution
Gross annual income: £50,000
Pension contribution: £5,000
If the £5,000 is a qualifying pension contribution taken into account under the statutory rules, the calculation may use an income figure around £45,000 before other relevant adjustments.
Example — 30% Pension Contribution
Gross annual income: £50,000
Pension contribution: £15,000
A large contribution is not automatically unlawful or ignored. However, where there is evidence suggesting deliberate diversion of income, either parent may ask CMS to consider the statutory variation rules.
Basic Percentages — After Step 2 Adjustments
1 Child
12% of adjusted gross weekly income up to £800.
For income above £800 and up to £3,000, an additional 9% applies to the amount above £800.
2 Children
16% of adjusted gross weekly income up to £800.
For income above £800 and up to £3,000, an additional 12% applies to the amount above £800.
3 or More Children
19% of adjusted gross weekly income up to £800.
For income above £800 and up to £3,000, an additional 15% applies to the amount above £800.
Shared Care — 52 Nights or More
| Agreed overnight stays per year | Reduction |
|---|---|
| 52–103 nights | 1/7 — approximately 14.29% |
| 104–155 nights | 2/7 — approximately 28.57% |
| 156–174 nights | 3/7 — approximately 42.86% |
| 175 nights or more | 50%, plus an extra £7 a week reduction for that child, subject to the statutory minimum and shared-care rules |
Other Children Supported by the Paying Parent
Where the paying parent supports relevant other children, CMS can reduce the gross weekly income figure before applying the basic or basic-plus percentages.
1 Other Child
11% reduction
2 Other Children
14% reduction
3 or More Other Children
16% reduction
Rates Applied
| Gross weekly income / circumstances | Rate | General result |
|---|---|---|
| Unknown or information not supplied | Default | Default statutory amount applies |
| Below £7 | Nil | £0 |
| £7–£100 or certain benefits | Flat | Normally £7 a week |
| £100.01–£199.99 | Reduced | Statutory reduced-rate formula |
| £200–£800 | Basic | 12%, 16% or 19% |
| £800.01–£3,000 | Basic Plus | Basic rate on first £800, then 9%, 12% or 15% on the remainder |
Basic Plus Category
Where adjusted gross weekly income is above £800 and up to £3,000, the first £800 is assessed using the basic percentage and the remainder is assessed at:
- 9% — one qualifying child
- 12% — two qualifying children
- 15% — three or more qualifying children
High Earner Category
CMS's maximum assessable gross weekly income is £3,000. Where the paying parent's gross weekly income exceeds that amount, the receiving parent may be able to seek additional maintenance through the court where the statutory conditions are satisfied.
The legal route is contained in section 8(6) of the Child Support Act 1991.
Travel Expenses — Contact Costs Variation
Minimum Amount
Current DWP guidance says the cost of maintaining regular contact with a qualifying child must generally be at least £10 a week before it can qualify as a special-expenses variation.
If accepted, the approved amount can reduce the income figure used for the maintenance calculation.
Evidence You May Need
- Fuel receipts
- Train or flight tickets
- Booking confirmations
- Mileage records
- Evidence of contact arrangements
- Other documents showing the actual cost
CMS Variations — Income That Can Be Added
A variation allows CMS to adjust the standard calculation where the paying parent's finances fall within one of the statutory additional-income grounds.
Unearned Income
Interest, dividends, rental income and other qualifying unearned income can be considered where the statutory threshold is met.
Assets
Notional income may be calculated from certain assets where their total qualifying value is at least £31,250.
Earned Income While on Flat Rate
Where the paying parent is on the flat rate but has qualifying earned income of at least £100 a week, that income may be considered.
Diversion of Income
CMS can consider a variation where the paying parent controls income and diverts it to another person or purpose so that it is not reflected in the standard calculation.
Company / Business Income
Dividends, rental income and alleged diverted income through a company may become relevant where the statutory variation criteria are met.
Trust / Investment Income
Certain taxable or unearned income from investments, trusts or similar sources may be relevant depending on the statutory category and evidence.
Company Vehicle Explained
A company vehicle is not automatically added separately to CMS income. Its relevance depends on how it is treated for tax purposes and whether a statutory variation ground applies.
When a Company Car May Matter
- It appears as a taxable Benefit in Kind reported to HMRC.
- The paying parent is a company director and the wider income picture is disputed.
- A statutory diversion-of-income application is made.
- Dividends or other company income are relevant under the variation rules.
Illustrative Example
Salary / taxable income after qualifying pension treatment: £50,000
Taxable company-car benefit: £6,000
The HMRC figure used by CMS may reflect taxable employment income including the benefit, depending on how the tax data is reported. The precise CMS figure must be checked against HMRC and the statutory income rules.
Company Director — Practical Record-Keeping
For company directors, the most important point is to keep clear evidence of salary, dividends, pension contributions, taxable benefits, company accounts, travel/contact costs and any other income relied upon by CMS.
Where CMS or the other parent alleges diverted income, ask which statutory variation ground is being relied upon and what evidence supports it.
Variation Categories — Legal Basis
The principal additional-income variation provisions are in Chapter 3 of Part 5 of the Child Support Maintenance Calculation Regulations 2012.
Regulation 69A
Notional income from qualifying assets exceeding the prescribed value.
Read Regulation 69AEvidence Matters
For any variation, keep documents that establish the actual income, asset, expense or company arrangement in dispute. CMS guidance says information supplied by one parent may be shared with the other so both parties have an opportunity to provide relevant information before a decision is made.
Current CMS Rates
The exact statutory result depends on all stages of the calculation.
| Gross weekly income / situation | Rate | General position |
|---|---|---|
| Income unknown or not provided | Default | Current GOV.UK default amounts: £38 for 1 child, £51 for 2, £64 for 3 or more. |
| Below £7 | Nil | £0 under the normal nil-rate income rule. |
| £7 to £100, or certain qualifying benefits | Flat | Normally £7 a week. |
| £100.01 to £199.99 | Reduced | Formula based on £7 plus a percentage of income above £100, adjusted where relevant for other children. |
| £200 to £800 | Basic | 12% for 1 child, 16% for 2, 19% for 3 or more, after the relevant Step 2 adjustments. |
| £800.01 to £3,000 | Basic Plus | Basic percentage on the first £800 plus 9%, 12% or 15% of the portion above £800 depending on number of qualifying children. |
| Above £3,000 | CMS cap | CMS calculations are capped at £3,000 gross weekly income; the receiving parent may be able to seek additional maintenance through the court. |
Basic and Basic-Plus Percentages
1 Qualifying Child
12% of adjusted gross weekly income up to £800, then 9% of the portion from £800 to £3,000.
2 Qualifying Children
16% up to £800, then 12% of the portion from £800 to £3,000.
3 or More
19% up to £800, then 15% of the portion from £800 to £3,000.
Relevant Other Children
CMS takes account of certain other children the paying parent supports. For income in the basic/basic-plus range, DWP's current guide shows these Step 2 reductions:
1 Other Child
11% reduction to the relevant gross weekly income figure.
2 Other Children
14% reduction.
3 or More
16% reduction.
For the reduced rate (£100.01–£199.99), a separate statutory table applies rather than simply deducting 11%, 14% or 16% and then using the ordinary basic-rate percentages.
Shared Care
Shared care for CMS purposes is based on qualifying overnight care. Regulation 46 says CMS should consider an agreement, a court order, or an established pattern of care when determining the expected number of nights.
| Annual shared-care nights | Reduction for that child |
|---|---|
| Fewer than 52 | No standard shared-care band reduction |
| 52–103 | 1/7 |
| 104–155 | 2/7 |
| 156–174 | 3/7 |
| Highest shared-care band | 50% plus an additional £7 weekly reduction for each child in that band, subject to the statutory rules |
Shared-Care Evidence
Court Orders
Relevant child-arrangements or contact orders can be important evidence of an expected care pattern.
Written Agreements
Written parenting agreements can help establish what the parents agreed.
Calendars
A contemporaneous overnight-care calendar can help show the actual pattern.
School or Medical Records
These may be relevant where they genuinely evidence who had care on disputed dates.
Messages
Messages about collections, returns and overnight stays may help evidence actual arrangements.
Travel Records
Tickets or travel records may support other evidence where long-distance contact is involved.
Variations — Special Expenses
Contact Costs
Regular costs of maintaining contact with a qualifying child can be considered. Current DWP guidance says the qualifying cost must be at least £10 a week.
Disability / Long-Term Illness
Some costs of supporting a relevant other child with disability or long-term illness may qualify.
Prior Relationship Debts
Certain debts from the former relationship may qualify where the statutory conditions are met.
Boarding School
The qualifying boarding/living element of school fees may be considered.
Former Shared Home
Certain mortgage, loan or insurance payments can qualify where the receiving parent and child remain in the home and the paying parent has no legal or equitable interest.
Evidence
Receipts, tickets, mileage records, invoices, agreements and other documents should be retained.
Variations — Additional Income
Income That May Be Added
- Rental income
- Dividends
- Interest and other qualifying unearned income
- Certain earned income where the flat/nil-rate conditions apply
- Notional income from qualifying assets
- Diversion of income
Current Official Thresholds
- Unearned income: at least £2,500 a year
- Qualifying assets: total value of £31,250 or more
- Relevant earned income for a flat-rate case: at least £100 a week
Company Directors, Dividends & Benefits in Kind
A company car or other benefit is not automatically a separate CMS “add-on”. What matters is how the benefit is reflected in taxable income and whether any statutory variation ground applies. Company directors may also face variation issues involving dividends, unearned income, assets or alleged diversion of income.
Do not use a general “lifestyle test” as if it were itself a statutory calculation rule. Ask which specific regulation or variation ground CMS is applying and what evidence supports the decision.
High Earners
CMS Maximum
The statutory CMS formula uses gross weekly income up to £3,000.
Possible Court Top-Up
Where the statutory conditions are met, the receiving parent may be able to apply to the court for additional maintenance above the CMS maximum-income calculation.
Evidence Standards & Good Administration
HMRC Records
Central to historic-income calculations and many annual reviews.
Income Evidence
Payslips, accounts, tax records and pension evidence may be important where current income or another financial issue is disputed.
Care Evidence
Court orders, written agreements and evidence of the established overnight-care pattern may be relevant.
Payment Records
Bank statements and references can be crucial where arrears are disputed.
Variation Evidence
Specific expenses or additional income should be supported by documents that address the statutory variation ground.
Decision Notices
Keep every calculation notice, annual review and mandatory reconsideration notice.
Protecting Yourself From Incorrect Arrears
An arrears figure depends on both the underlying liability and the payment history. If either is wrong, the balance may be wrong.
Keep Payments
Bank statements, standing orders, payment references, receipts and screenshots.
Keep Shared-Care Records
Calendars, agreements, orders and contemporaneous communications.
Keep Calculation Evidence
Income records, pension evidence, variation material and annual-review notices.
Build a Timeline
Record the liability amount, changes, payments and claimed balance month by month.
Ask for a Breakdown
Ask CMS which liability periods and payment credits produce the arrears figure.
Challenge the Underlying Decision
If the arrears arise from an incorrect appealable calculation, use the appropriate decision-challenge route as well as disputing payment records.
If You Disagree With a Calculation
Check the Calculation Notice
Check income, effective date, pensions, relevant other children, qualifying children, shared care and variations.
Ask CMS for an Explanation
Ask exactly what evidence and statutory rule produced the disputed figure.
Submit Evidence
Provide focused documents relevant to the disputed calculation point.
Mandatory Reconsideration
For an eligible decision in Great Britain, request mandatory reconsideration within the applicable deadline shown on the decision notice.
Mandatory reconsiderationIndependent Tribunal
If still dissatisfied after mandatory reconsideration, an appeal may be available to the Social Security and Child Support Tribunal.
Appeal guidanceComplaint for Service Failure
Use the complaint route for delay, communication problems, evidence-handling failures or maladministration.
CMS complaintsData Rights
Subject Access Request
You can ask for copies of personal information held about you, which can help establish what CMS records contain.
ICO SAR guidanceRectification
You can ask for inaccurate personal data to be corrected where the UK GDPR right applies. This is separate from appealing a statutory maintenance decision.
ICO rectificationOfficial Calculators & Guidance
Official CMS Calculator
Provides an estimate based on the information entered. It is guidance and does not replace an actual CMS calculation.
Use calculatorHow CMS Works It Out
The current DWP step-by-step calculation guide, updated in 2026.
Read calculation guideNorthern Ireland
How Maintenance Is Calculated
NI Direct explains the six-step Northern Ireland calculation process.
NI calculation guideNI Calculator
Official guidance on using the child-maintenance calculator for Northern Ireland.
NI calculator guidanceNI Appeals & Complaints
Official Northern Ireland route for challenging a decision or complaining about service.
NI appeals and complaintsIndependent Help Across the UK
Citizens Advice Scotland
Free independent advice through Scotland's Citizens Advice network.
Scotland adviceIndependent Case Examiner
Independent examination of eligible maladministration complaints after the CMS/DWP complaint process.
ICEParliamentary Ombudsman
Final-stage route for unresolved complaints about UK government departments; an MP referral is required.
PHSOCalculation Check Checklist
- Check the annual and weekly gross income used.
- Check which tax year supplied the HMRC figure.
- Check whether current-income rules should apply.
- Check qualifying pension contributions.
- Check the number of relevant other children.
- Check the number of qualifying children.
- Check which statutory rate was used.
- Check shared-care nights and the correct band.
- Check any variation for expenses or additional income.
- Check the effective date of every change.
- Keep all payment records and decision notices.
- Ask CMS for a written explanation where any part of the calculation is unclear.
Key Message
Child maintenance calculations should follow the statutory formula and the evidence relevant to the case. Both paying and receiving parents should check the figures rather than assuming every calculation is automatically correct.
Income, pensions, other children, shared care, variations and effective dates can all materially change liability. Good records and prompt use of the correct reconsideration or appeal route can be vital where a calculation is disputed.
Check the numbers. Keep the evidence. Understand the rule being applied. Challenge errors through the correct legal process.