FLiP’s Child Maintenance Calculator for The Red Book 2023 Edition


This calculator is best read in conjunction with the Lexis Nexis Redbook (which can be purchased here). It seeks to provide:

1. A guide to the jurisdiction of the CMS;

2. The steps that would be taken by the CMS in completing its calculation (including the additional steps that are taken if there were a variation application);

3. The out-turn of that calculation;

4. The calculation that emerges from the ‘GW v RW’ uncapped formula a) up to £650,000; and b) above that cap; and

5. James -v- Seymour [2023] EWHC 844 (Fam) calculations.

Before proceeding to the calculator, the first step is to know whether the CMS has jurisdiction and the second will always be to identity who the paying parent is. Check the position below.

Does the CMS have jurisdiction? →

1. Geography: 

Is the child in the UK? Are both parents in the UK? (or if the NRP is abroad, then are they working for a UK registered company or in the armed forces or on Government service (s44(1) CSA ’91)?

2. Age

Do the child subject(s) qualify for child benefit?

(Broadly are they children in secondary education?) (r76 of 2012 no 2677). Please refer to table at 2.195[1] of the Redbook for details.

3. Parentage

Is the claim against a legal parent? Claims can only be made against a natural / adoptive parent or a parent who has a parental order under the HFEA (s54 CSA ’91).

(See definition of parent at s54 CSA’91).

4. Separation

Is the claim against a parent living separately from the child? Claims cannot be made unless the parents have separated (s3 CSA ’91).

5. Order free

Will an application be free from an order? Applications to the CMS are impermissible if there is a maintenance order in place and it is less than 12 months old (s4(10) CSA ’91 and for meaning of maintenance order see s8(11)).

6. Unequal care

Is care for this child unequal? Where care is equal (this is not a simple count of overnight care) then there can be no parent with care and no CMS jurisdiction (r50 of 2012 no 2677).

If yes to all of the above application is to the CMS.

If no then application is [probably] to the court. Please note that the applicability of the formula is very much an ongoing debate.

We also do not know whether a broad approach to the formula is appropriate or whether the court is expected to carry out a more careful analysis including potential variations.

Who is the parent with care? →

The financial claim is made by the a person or parent with care (“PWC”) against the other legal parent who is the “non resident parent” or “NRP”.

Where care is shared these identities must be allocated.

  • Regulation 50(3) of 2012 no 2677 permits the CMS to assume that the parent in receipt of child benefit is the parent with care; but
  • Evidence may then be produced for a determination – often this will only be done on an appeal, which will involve delay.

There are the following categories of NRP:

1) those who are exempt from payment (who pay “the nil rate”) (r45 of 2012 no 2677);

2) those with incomes of under £100 who pay “a fixed rate” levy of £7 per week (para 4 sch1 CSA ’91);

3) those whose incomes are between £100 and £200 p/w who pay “a reduced rate” (in effect a reduced percentage of their income enters the calculation) (r43 of 2012 no 2677);

4) those with incomes up to £3,000 gross pw, to whom “the basic rate” formula applies (para 2 sch1 CSA ’91);

5) those with incomes above £3,000 pw but below £12,500 pw, who in Mostyn J’s view should generally pay for children at the same level of % levy as is mandated by the formula, notwithstanding that the formula no longer applies to them for this higher segment of earning;

6) those earning at higher levels still, for whom there is no such guideline.

Categories 4) 5) and 6) are addressed under this calculator.

A new approach should be taken to categories 5) and 6) according to Mostyn J in James v Seymour [2023] EWHC 855 (Fam).

Our Expert Team


For questions concerning the calculator or for bespoke advice, contact one of expert team below.