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James v Seymour [2023] EWHC 844 (Fam) – Mostyn J refines approach to Child maintenance "Top-up" awards

Posted on 16 October 2023

In a previous decision (CB v KB [2019] EWFC 78) Mostyn J suggested that, where a paying parent's income is between the Child Maintenance Service (CMS) statutory maximum (£156,000) and £650,000, that the CMS formula should still be applied.

In James v Seymour the wife sought a variation of child periodical payments (pps) that had been ordered in 2014. She sought to apply the CB v KB formula. The Circuit Judge declined to do so, although she did increase the pps. The wife appealed, one of her grounds being that the Judge didn't follow the CB v KB formula.

Mostyn J dismissed the appeal. He did not consider the CB v KB formula to apply where a parent was seeking a variation of a previously-made child maintenance order. Rather, the starting point should be the previous order + inflation.

He further decided that his CB v KB formula was too simplistic and gave rise to odd results (namely that payments for a single child are significantly higher than for each child where there are two or three children).

He decided to come up with his own new formula, which he calls the "Adjusted Formula Methodology" (AFM). He considers that the AFM give a Child Support Starting Point (CSSP), which the court can depart from, but which, if the court followed, would not be susceptible to challenge on appeal.

He considered it would not apply where:


  • there are four or more children for whom child support is to be paid, or
  • the payer's earnings are more than £650,000, or
  • the payer's income is largely unearned, or
  • the payer lives on capital.

In such circumstances maintenance should be worked out by reference to the statutory provisions, without using the AFM.

He also noted that every child maintenance case, whether it is formulated as a claim for a HECSA or for a conventional award, requires a budget.

Antonia Felix says: The decision in CB v KB had the advantage of simplicity in terms of the starting point for a child maintenance claim against a high earner. Although it's correct that the percentage calculations used by the CMS are somewhat skewed in favour of households with one child rather than multiple children, CB v KB was consistent with the statutory formula. It's not clear why there should be a different formula from £156,000 - £650,000, or why that formula should be the one announced by Mostyn J. Moreover, he considers that school fees met by the paying parent should be taken off the calculation of their income, which (in his own example) would result in a parent earning £157,000 paying less than one that earns £156,000, given the CMS does not deduct school fees.

Mostyn J emphasised that the AFM produces a loose starting point which a decision-maker can summarily choose to accept or reject without fear of appellate review. The judicial uptake on this new formula remains to be seen. At present, expect to see it used on behalf of the paying parent.

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