Estimate child maintenance payments — UK & US
Based on the UK Child Maintenance Service (CMS) Basic Rate formula.
In the UK, the Child Maintenance Service (CMS) uses a formula based on the paying parent's gross income. The base rates are 12% for 1 child, 16% for 2 children, and 19% for 3 or more. These rates are reduced if the paying parent has other dependent children living with them, and further reduced if the child spends overnight stays with them.
In the US, the majority of states use the Income Shares Model, which considers both parents' incomes. The combined income determines a total child support obligation from state-published tables, and each parent is responsible for their proportional share based on income.
The UK Child Maintenance Service uses the paying parent's gross weekly income. The basic rate is 12% of gross income for 1 qualifying child, 16% for 2, and 19% for 3 or more. These percentages are reduced by approximately 1/7th for each child the paying parent has in their own household. If the child spends 1–2 nights per week with the paying parent, the amount is reduced by 1/7th per night; 3 nights reduces it further; at 4+ nights (shared care), the amount is halved. Income above £3,000/week is not included in the calculation.
Most US states use the Income Shares Model. Both parents' gross incomes are combined to find a total support obligation from state guidelines tables. Each parent then pays their proportion — for example, if you earn 60% of the combined income and are the non-custodial parent, you pay 60% of the total obligation. Some states like New York and Texas use a Percentage of Income model based only on the non-custodial parent's income, with set percentages per child (17% for 1, 25% for 2, 29% for 3, etc.).
In the UK, CMS arrangements are reviewed annually, and either parent can request an immediate review if circumstances change significantly (e.g., income changes by 25% or more). In the US, either parent can petition the court for a modification if there is a "substantial change in circumstances" — typically a job loss, significant income change, change in custody, or changes in the child's needs. Courts don't modify orders automatically; you must apply.
In the UK, the CMS has enforcement powers including deducting from wages, bank accounts, or benefits, and can apply for a court order, driving licence suspension, or even imprisonment. In the US, enforcement is handled by state child support agencies — they can garnish wages, intercept tax refunds, suspend driving licences, report to credit agencies, and in serious cases pursue criminal charges for non-payment.