CSA Percentage Calculator

Unlike the historic 1993 and 2003 CSA schemes (which applied flat percentages of 15%, 20%, or 25% of net income), the 2012 CMS statutory scheme applies a two-tier marginal gross formula.

This design prevents child maintenance from becoming an excessive disincentive to career progression. Once a paying parent's gross income exceeds £800 per week (£41,600 per year), the marginal child maintenance rate drops by 3 to 4 percentage points on all earnings between £800 and the £3,000 weekly statutory ceiling.

For paying parents earning between £100 and £199.99 per week, the CMS uses the Reduced Rate formula to bridge the gap between the £7 flat rate and the 12% basic rate:

The multiplier is 17% for 1 child, 25% for 2 children, and 31% for 3 or more children. If the paying parent has resident children in their current household (ROC), these percentages are reduced accordingly under Regulation 43.

Before applying the 12%, 16%, or 19% rates, gross weekly income is sliced down if the paying parent lives with other children. For example, if a parent earns £600 per week and has 2 children in their new household, an immediate 14% deduction (£84) is removed, leaving £516 as the base for the qualifying child's assessment.