Deep dive · Updated 07/07/2026
Variations: when the standard formula can be departed from
The formula is rigid by design, but sections 28A–28G of the Child Support Act 1991 allow either parent to apply for a "variation" in defined circumstances. Variations are the battleground of most contested cases — and the area where tribunals most often change CMS decisions.
Grounds for paying parents: special expenses
A paying parent can ask for defined costs to be deducted from gross income before the formula is applied. Each expense generally only counts to the extent it exceeds £10 a week.
| Ground | What qualifies | Notes |
|---|---|---|
| Contact costs | Travel and accommodation to maintain contact with the qualifying child | Must be a set pattern of contact; fuel, fares, lodging |
| Disability of a relevant other child | Costs attributable to a disabled child in your household | No £10 threshold on this ground |
| Prior debts | Debts incurred for the family before separation, from which the receiving parent or child still benefits | Narrowly construed — evidence the purpose |
| Boarding school fees | The boarding (not tuition) element for the qualifying child | Capped — cannot reduce income by more than 50% |
| Prior mortgage payments | Payments on the former home's mortgage where the receiving parent and child still live there and you have no interest in it | See LM v SSWP [2024] UKUT 259 for current guidance |
Grounds for receiving parents: additional income
| Ground | Threshold | What it catches |
|---|---|---|
| Unearned income | £2,500+ a year | Rental profits, dividends, interest, trust income — anything taxable but not "earned" |
| Earned income (flat-rate payers) | £100+ a week | A paying parent on benefits who also has earnings or pension income |
| Diversion of income | None | Income the paying parent controls but routes elsewhere — salary paid to a new partner, profits retained in a company, excessive pension contributions, benefits in kind |
| Notional income from assets | Assets over £31,250 | Since December 2018: non-income-producing assets (second homes, land, share portfolios, money) are deemed to yield 8% a year, added to income |
Variations are application-driven. The CMS does not routinely check for rental income, dividends or company structures — if nobody applies, the standard (possibly artificially low) figure stands. Equally, a paying parent with heavy contact costs who never applies simply pays more than the law requires. Know the grounds; use them.
How a variation application runs
Apply
By phone or in writing (writing is better — it fixes the date and content). State the ground, the facts, and attach what evidence you have. There is no fee.
Preliminary sift
The CMS can reject applications with no prospect of success. Rejection at this stage is itself a decision you can take to mandatory reconsideration.
Representations
The other parent is told the ground (not your full evidence) and can comment. Expect this — and if you are on the receiving end of a variation application, engage with it; silence rarely helps.
Decision — the "just and equitable" test
Even where a ground is made out, a variation is only granted if it would be just and equitable in all the circumstances (s.28F). The Upper Tribunal in PP v SSWP [2022] UKUT 286 confirmed this is a broad discretion: decision-makers can grant in part, and must not treat it as all-or-nothing.
Challenge
Any variation decision — grant, refusal or amount — carries the usual MR and appeal rights for both parents. Tribunals decide variations afresh and have information-gathering powers the CMS rarely uses: directions for company accounts, bank statements, and oral evidence under oath.
Evidence that wins variation cases
- Unearned income: the paying parent's SA302/tax return entries (the tribunal can direct disclosure), Land Registry entries for rental property, Companies House accounts.
- Diversion: Companies House filings showing retained profits or a partner's directorship; lifestyle inconsistent with declared income is a starting point but needs documentary anchors.
- Notional income: evidence the asset exists and its value — valuations, mortgage statements, completion statements.
- Special expenses: a contact schedule, fuel/fare receipts, loan agreements and statements for prior debts.
Sources
| Source | Type | Date | Credibility |
|---|---|---|---|
| DWP — Variations explained: paying parents | Official guidance | 2023 | High |
| DWP — Variations explained: receiving parents | Official guidance | 2023 | High |
| Commons Library CBP-7773 — Variations, including the notional income criterion | Parliamentary briefing | Current | High |
| PP v SSWP (CSM) [2022] UKUT 286 (AAC) | Case law | 2022 | High |
| LM v SSWP & NM [2024] UKUT 259 (AAC) — commentary | Case law + practitioner commentary | 2024 | High (case); Medium (commentary) |