When it comes to determining child maintenance in high-income cases, the standard framework provided by the Child Maintenance Service (CMS) in England and Wales can fall short. The CMS formula applies only up to a capped gross weekly income (currently £3,000, or £156,000 a year), which can leave a gap in provision where one parent earns significantly more. In such cases, the courts may step in to assess what level of maintenance is appropriate.
One approach that has gained recognition in this context is the “Mostyn Formula”, which is a judicially developed guideline often used as a starting point in so-called “top-up” child maintenance cases where the paying parent’s income exceeds the CMS threshold. The formula aims to provide a degree of consistency and fairness in what can otherwise be highly discretionary decisions.
In simple terms, the Mostyn Formula applies a percentage (typically around 15%) to the paying parent’s gross income above the CMS cap, up to a further upper limit (often £650,000 per annum, though this is not fixed). The resulting figure is then adjusted to reflect the number of children and the level of overnight contact they have with the paying parent. The intention is to mirror, to some extent, the structure of the CMS calculation while extending it to higher income levels.
One of the key advantages of the Mostyn Formula is that it introduces a measure of predictability. High-income cases can be complex and emotionally charged, and having a recognised approach can help reduce conflict and streamline negotiations. It can also assist legal professionals and mediators in guiding discussions, particularly where parties are seeking to avoid costly court proceedings.
However, it is important to note that the formula is not applied rigidly. The court retains full discretion and will consider the individual circumstances of each case. Factors such as the child’s needs, the standard of living they would have enjoyed had the family remained intact, and the financial resources of both parents all play a role.
In some cases, the court may depart significantly from the formula if it considers that a different outcome is justified.
Critics of the Mostyn Formula argue that it can still produce arbitrary results, particularly given the absence of a clear statutory basis. Others suggest that it may not adequately reflect the real needs of children in very high-income households. Nonetheless, it remains a useful tool in the absence of more detailed legislative guidance.
In practice, the Mostyn Formula is best viewed as a helpful benchmark rather than a definitive answer. For separating parents navigating high-income child maintenance issues, it can provide a valuable reference point-but one that should always be considered alongside broader principles of fairness and the best interests of the child.
Key Aspects of the Mostyn Formula
- Target Audience: High earners (£156,001 – £650,000 gross annual income).
- The Calculation: 1.
Identify Gross Income:
Use the paying parent’s gross annual income. 2.
Deduct Household Children:
Reduce income based on children in the payer’s home (11% for 1, 14% for 2, 16% for 3+ children). 3.
Deduct Pension Contributions:
Subtract actual pension payments made. 4.
Deduct School Fees:
Subtract school fees/extras, “grossed up” to account for tax. 5.
Apply Tariff:
Apply a tariff of 2.4% for one child, or 3% for two/three children, to the surplus income above £156,000, added to the base CMS payment for the first £156,000.
When it is Not Applied
The court will generally not use this formula if the paying parent’s gross income is over £650,000, there are four or more children, income is primarily unearned, or if the payer has no income or lives on capital. It is meant for “top-up” scenarios, providing a more balanced alternative to earlier methods which were criticised for producing excessively high figures.