24th Aug 2023

Introducing FLiP’s Child Maintenance Calculator

By James Pirrie

Introducing FLiP’s Child Maintenance Calculator


We really appreciated the opportunity to contribute to the Child Support pages to this year’s Red Book, building on the great work that has been done by David Burrows over many years.

We have tried to make the new Child Support chapter practical and accessible and have looked at the problems that we know practitioners wrestle with for their clients day in day out.

Having been doing this work for 30 years now, we know that practitioners often end up with what can feel like a half-remembered jumble of rules.  What we have tried to provide is a structured way for working out:

  • whether the CMS has jurisdiction;
  • who can make a claim;
  • what the CMS will award;
  • what is its process;
  • whether a variation can be applied for (and if so what the impact will be); and
  • how the various judicial dicta might apply in particular circumstances to indicate an appropriate award when the courts have jurisdiction.

Text in a book can only go so far. What we have created and what is accessible here to run alongside is a calculator, with reminders about the key rules and considerations that apply to each of the steps along the way:

  • we provide guidelines about when the CMS has jurisdiction;
  • set out the tests for deciding who is the parent with care;
  • and then provide a calculator to deliver the basic assessment that the CMS should carry out in your case, through the input of the five core variables: 1) income, 2)pension contributions, 3)children in the paying party’s home, 4) children being paid for and 5)overnight stays).

It takes in where the paying parent has dependent children in their household but also looks at where the paying party has multiple obligations to a number of persons with care.

The print out can show:

  • the range of obligations depending on overnight stays; or
  • child specific calculations for example where overnights differ between children.

It goes on to consider, give guidance on and provide calculations and print outs for the different categories of variation that might apply.

We have Mostyn J’s guidance in James -v- Seymour (2023), distancing himself from the earlier “just uncap the formula, at least up to incomes of £650k” approaches developed in cases such as GW v RW (2003), re M-M (2014), re TW & TM (2015) and CB v CK (2019).  The latest guidance attempts to answer criticisms of the “uncap the formula” approach and may be the way forward.

As things stand we provide:

  • uncapped formula calculations; and
  • the James -v- Seymour calculations.

We hope our professional colleagues will find the calculator useful and we hope for feedback.  We think we have it spot on and have tested it multiple times, but there are lots of lines of code and we know that it just takes one glitch and one set of unusual circumstances, so please do get in touch (jp@flip.co.uk) if you encounter problems.

To discuss the calculator or child support related queries, do contact James Pirrie below. James is a specialist in child maintenance and has previously appeared before the House of Commons Public Accounts Committee to talk about the practicality of the rules surrounding the Child Maintenance Service.