What does the CMS formula say you should pay?

The Child Maintenance Service uses a formula based on the paying parent's gross weekly income from HMRC records, the number of qualifying children, and the amount of overnight shared care. There are five rate bands: Nil (income below £7/week), Flat (£7-£100/week, fixed at £7), Reduced (£100-£200/week), Basic (£200-£3,000/week), and Basic Plus (above £3,000/week). For the Basic rate, the percentages are 12% of gross income for one child, 16% for two children, and 19% for three or more. Shared overnight care reduces the amount by a fraction depending on how many nights the paying parent has the children.

The minimum is the Flat rate of £7 per week, which applies when the paying parent's gross weekly income is between £7 and £100. If income is below £7 per week, or if the paying parent receives certain means-tested benefits, the Nil rate applies and no maintenance is payable. The Flat rate of £7 per week applies regardless of how many children are involved. Private arrangements between parents can set any amount, but if either parent applies to the CMS, the statutory formula takes over.

Yes. If the paying parent has the children for at least 52 nights per year (roughly one night per week), the maintenance amount is reduced. The reduction is a fraction: 1/7 for 52-103 nights, 2/7 for 104-155 nights, 3/7 for 156-174 nights. If the paying parent has 175 or more nights per year (near-equal shared care), only the Flat rate of £7 per week per child applies. The shared care adjustment only applies to the Basic and Basic Plus rate bands, not to the Flat or Reduced rates.

The CMS uses the paying parent's gross income as reported to HMRC through Real Time Information. For employees, this is gross pay before tax and National Insurance. For self-employed parents, the CMS uses the gross income figure from the most recent tax return. The CMS can also include unearned income such as dividends, rental income, and pension income if the receiving parent requests a variation. Income from a new partner is not included. If the paying parent's income has changed by 25% or more since the last assessment, a current income figure can be used.

Yes. A family-based arrangement is a private agreement between parents without CMS involvement. There is no fee, and parents can agree on any amount and payment schedule. If both parents cooperate, this is the cheapest and simplest option. However, private arrangements are not legally enforceable. If either parent later applies to the CMS, the statutory formula will be applied regardless of any previous private agreement. The CMS charges a £20 application fee and, if using the Collect and Pay service, takes 20% from the paying parent and 4% from the receiving parent on each payment.

Child maintenance continues until the child turns 16, or 20 if the child is in full-time non-advanced education such as A-levels. It can also end earlier if the child marries, enters a civil partnership, or leaves full-time education before 16. University education does not automatically continue the obligation. The obligation does not automatically end when a child turns 18 if they are still in qualifying education. Either parent can apply to have the amount reviewed if circumstances change, such as a significant income change or change in overnight care arrangements.

Self-employed parents present a challenge because their income can fluctuate and may be structured to minimise taxable income. The CMS uses the gross income figure from the most recent self-assessment tax return. If the receiving parent believes income is being understated, they can request a variation asking the CMS to consider additional income sources, lifestyle inconsistent with declared income, or assets that generate income. The CMS has the power to investigate and adjust the figure used in the calculation. Deliberately understating income for the purpose of reducing maintenance is treated seriously by the CMS.

Yes. If the paying parent has other qualifying children living with them or with a different parent, the gross income used in the calculation is reduced before applying the percentage rates. One other qualifying child reduces the gross income by 11%, two by 14%, and three or more by 16%. This reduction acknowledges that the paying parent has financial responsibilities for other children that affect their available income. Step-children do not qualify unless they are legally adopted.

Self-employed paying parents present a challenge for the CMS because their income can fluctuate and may be structured in ways that reduce the taxable figure. The CMS uses the gross income figure from the most recent self-assessment tax return. If the receiving parent believes the paying parent's declared income understates their actual financial position — for example, because their lifestyle appears inconsistent with their declared income, or because they hold significant assets — they can request a variation asking the CMS to consider additional income sources. The CMS has investigative powers and can adjust the income figure used in the calculation if evidence supports doing so. Self-employed parents who take most of their remuneration through dividends rather than salary should be aware that HMRC and CMS both have powers to look through remuneration structures that appear primarily designed to reduce assessed income, particularly following recent tribunal cases on this issue.

Yes. A family-based arrangement is a private agreement between parents without CMS involvement. There is no fee, and parents can agree on any amount and payment schedule. If both parents are cooperative, this is the simplest and cheapest option. However, private arrangements are not legally enforceable — if either parent later applies to the CMS, the statutory formula is applied regardless of any previous private agreement. The CMS charges a £20 application fee (waived in domestic violence cases). If parents use Direct Pay, there are no ongoing fees: the CMS calculates the amount and the paying parent pays the receiving parent directly. If parents use Collect and Pay — because direct payment has broken down — the paying parent pays a 20% surcharge and the receiving parent receives 4% less than the calculated amount. These fees are designed to incentivise cooperative private arrangements over the managed service.

No. Income from a new partner or spouse does not affect the child maintenance calculation. The CMS formula uses only the paying parent's own gross income from employment, self-employment, pensions, and certain other sources. A paying parent who remarries or moves in with a high-earning new partner pays exactly the same child maintenance as before the new relationship began, because the new partner's income is entirely excluded from the calculation. What does affect the formula is if the paying parent has other qualifying children from a different relationship living with them: in that case, their gross income is reduced before the formula is applied (by 11% for one other child, 14% for two, 16% for three or more), which reduces the maintenance payable for children from the previous relationship. This adjustment recognises the paying parent's financial responsibilities to children currently living in their household.