How the Child Maintenance Service Calculates Payments in 2025: A Guide for Both Parents

Most separated parents reach some kind of informal agreement about money when they first split. Some of those arrangements hold up. Many do not. When they break down, or when one parent wants a formal, enforceable figure from the outset, the Child Maintenance Service steps in. The CMS replaced the old Child Support Agency in 2012 and uses a standardised formula to work out how much the non-resident parent should pay each week. Understanding that formula in detail gives both sides a realistic picture before any application is made.

The calculation is not complicated once you break it into its component parts. Start with the paying parent's gross income. Apply the right rate based on that income and the number of qualifying children. Then adjust for any shared care arrangements. Our child maintenance calculator runs through those steps automatically, but understanding the logic behind the numbers helps you spot errors and know where you stand if something seems wrong.

The Four CMS Rates and What Triggers Each One

The CMS splits paying parents into four income bands, each with a different treatment. The nil rate applies where gross weekly income is below £7. At that level, no maintenance is payable. The flat rate of £7 per week applies to parents with weekly gross income between £7 and £100. It also applies to parents receiving certain benefits regardless of income, including Universal Credit, Jobseeker's Allowance, Income Support, Incapacity Benefit and similar. The flat rate does not change with income within that band. Seven pounds per week is the floor.

Above £100 per week gross, a reduced rate applies on a sliding scale until weekly income reaches £200. Within this band, as income rises from £100 toward £200, the weekly payment increases from £7 toward the amount that the basic rate formula would produce at £200 per week. The reduced rate exists to smooth the transition between flat rate and basic rate rather than creating a cliff edge where a small pay rise suddenly multiplies the maintenance obligation.

The basic rate is where most working parents land. It applies to gross weekly income between £200 and £3,000. This is calculated as a straight percentage of gross weekly income depending on the number of qualifying children.

The cap at £3,000 per week (roughly £156,000 a year gross) means the CMS formula has a ceiling. Parents with very high incomes who want additional maintenance beyond the CMS cap must pursue that through the family courts rather than the CMS, which can take into account the standard of living the children would have enjoyed had the family remained together.

How Gross Income Is Assessed

The CMS pulls income data directly from HMRC. For employed parents this is typically the gross annual salary from the most recent tax return, converted to a weekly figure by dividing by 52. This includes all employment income, overtime, bonuses and benefits in kind that are taxable. It does not include amounts that are genuinely non-taxable.

For self-employed paying parents, the CMS uses the gross profit figure from the most recent self-assessment return. This is after allowable business expenses but before income tax and National Insurance. That point matters because self-employed parents sometimes assume that business expenses have reduced their assessable income substantially, but only legitimate trading expenses that HMRC accepts are deducted. Personal drawings from a company, dividends from a closely held limited company, and notional salary reductions to shift income to a partner are all scrutinised under the variations process.

Capital gains can also be brought into the calculation where the paying parent has a pattern of realising capital gains as a substitute for income. This is more common among business owners and those with investment portfolios who time disposals in ways that flatten their declared employment or self-employment income. The receiving parent can apply for a variation citing this. Pension contributions do not reduce the gross income figure used by the CMS, which surprises some paying parents. The CMS uses gross income before pension deductions. A parent paying £1,000 a month into a pension still has that full income counted by the CMS even though their take-home pay reflects the pension contribution.

To check how your gross income translates into take-home pay and understand the difference between what you earn and what the CMS sees, the UK salary calculator gives you a breakdown of gross to net income including pension and tax effects.

Shared Care Adjustments: How Overnight Stays Reduce Payments

The maintenance formula assumes the paying parent has no overnight care of the qualifying children. Where nights are shared, the CMS applies a deduction that recognises the paying parent is directly meeting some of the children's costs during their time. The deduction is structured in bands based on average nights per week.

These deductions only apply to nights that are actually occurring on a regular basis. Planned arrangements that are not happening in practice carry no weight. The CMS will ask for evidence of the actual overnight pattern, which can include school records, medical appointments and similar documentation. Where parents dispute the number of nights, the CMS will make a finding based on available evidence and both parties can challenge that finding through the mandatory reconsideration process.

Where the paying parent has other qualifying children living with them (from a subsequent relationship, for example), the CMS applies a deduction to the income figure before calculating maintenance for the children from the original relationship. The deduction is 12% of gross income for one relevant other child, 16% for two, and 19% for three or more. This calculation stacks across multiple sets of children in a structured way.

Direct Pay vs Collect and Pay

After a CMS assessment, both parents choose how to handle the actual transfer of money. Direct Pay means the paying parent transfers funds directly to the receiving parent on the CMS schedule. The CMS sets the amount and the payment dates but does not handle the money itself. There are no service charges under Direct Pay. This option suits parents who can manage the practical arrangement between themselves without conflict.

Collect and Pay means the CMS acts as a financial intermediary. It collects from the paying parent and passes the money to the receiving parent. The service comes with a cost that both parents share. The paying parent has 20% added to their maintenance liability. The receiving parent has 4% deducted from what they receive. A parent paying £400 per month in maintenance under Collect and Pay actually pays £480, while the receiving parent gets £384. That gap reflects the cost of the service.

The CMS actively tries to direct parents toward Direct Pay. The financial incentive is substantial. But where there is a history of non-payment, where the relationship is too hostile to allow direct contact, or where the paying parent has already missed payments, Collect and Pay provides a structure that enables enforcement action more readily.

How to Challenge a CMS Assessment

Either parent who believes the CMS has made an error has a defined route to challenge the decision. The first step is a mandatory reconsideration. You must request this within one month of the original decision. The CMS reviews the case internally. You provide your grounds in writing and any evidence that supports your position. The CMS must issue a fresh decision within a set timeframe. This process does not cost anything and does not require a solicitor, though having documentation organised clearly helps significantly.

If the mandatory reconsideration does not resolve the issue, the next step is an appeal to the First-tier Tribunal (Social Entitlement Chamber). The Tribunal is independent of the CMS and can substitute its own decision for the CMS decision. Tribunal hearings are more formal than the internal reconsideration but are designed to be accessible without legal representation. Common grounds for appeal include errors in the income figure used, failure to apply the correct shared care deduction, incorrect identification of qualifying children, and failure to apply a variation correctly.

Where you believe the income figure is wrong but cannot prove it through the reconsideration process, a variation application runs alongside or after a reconsideration. Variations for lifestyle inconsistent with declared income, hidden assets, or diverted income require you to provide evidence that the CMS then investigates. These are adversarial by nature but the CMS has real investigative powers and can compel the paying parent to provide financial information.

What Happens When Income Changes After an Assessment

CMS assessments are not fixed for life. They are reviewed annually using updated HMRC data. But significant income changes mid-year do not automatically trigger a reassessment. If a paying parent loses their job, takes a major pay cut, or their business income drops sharply, they should contact the CMS promptly. A change in gross weekly income of 25% or more from the figure used in the current assessment can trigger a review ahead of the annual cycle.

The same applies in reverse. If a receiving parent knows the paying parent has taken a substantial pay rise or changed jobs for significantly higher pay, requesting an income review is the mechanism to update the calculation. The CMS will contact HMRC for updated data and recalculate from there. Keeping records of any income changes, whether your own or the other parent's, and acting quickly when they occur rather than waiting for the annual review cycle, tends to produce fairer outcomes for both sides over time.