Methodology and sources

This page lists every figure the calculator uses, where it came from and what the tool deliberately does not model. If a number on this site is not on this page, it is a bug.

Rates in use

All figures are for the 2026 to 2027 tax year and were verified on 2026-08-14 against GOV.UK: Rates and thresholds for employers 2026 to 2027, which HMRC last updated on 5 June 2026.

The date the SMP rate changes

HMRC applies the SMP rate from 2026-04-05 but every other statutory payment rate from 2026-04-06. That one-day difference is easy to miss and easy to get wrong, so it is encoded as a named constant rather than left implicit.

How the calculation works

1. Eligibility. Average weekly earnings are compared to the lower earnings limit. Below it, SMP is not payable at all and the calculator says so rather than returning a small number.
2. Weeks 1 to 6. 90% of average weekly earnings, with no cap. High earners genuinely receive 90% of full pay here.
3. Weeks 7 to 39. The lower of £194.32 and 90% of average weekly earnings.
4. Weeks 40 to 52. No statutory pay. These weeks are shown in the schedule as unpaid rather than omitted, because the gap between 39 paid weeks and 52 leave weeks is the single most common planning mistake.
5. Occupational schemes. Where the enhanced rate is inclusive of SMP, which is the usual arrangement, the employer tops up to the target and the top-up is never negative. Where it is on top, both are paid.

Assumptions and limits

• Continuous employment is assumed. The calculator does not test the 26-week rule. If you have not been with the same employer for 26 weeks up to the qualifying week, SMP is not payable whatever the earnings test says.
• All figures are gross. SMP is treated as earnings and is subject to Income Tax and National Insurance through PAYE. No deductions are applied here.
• No dates are calculated. The qualifying week, leave start and end dates need a date engine and HMRC already publishes an official one.
• Maternity Allowance is out of scope, as are Statutory Adoption Pay and Shared Parental Pay, which have their own rules despite sharing the same weekly rate.
• Employer recovery is calculated on statutory pay only, not on any occupational top-up, which is not recoverable.

Testing

The engine is covered by unit tests whose expected values were worked out by hand from the GOV.UK rates page. They include the boundary where 90% of earnings crosses the standard rate, the lower earnings limit to the penny, the 39 against 52 week split, and the rule that an occupational top-up can never go negative when SMP already exceeds the target.

Review schedule

Statutory payment rates change every April. This site is reviewed each March in advance of the new tax year, and again whenever HMRC republishes the rates and thresholds page.

Corrections

If a figure here is wrong or out of date, report it via the about page with the GOV.UK source that contradicts it. Corrections to statutory figures are treated as urgent.