When your weekly payday falls on 5 April, the calendar squeezes in a 53rd payment. Here is why it is taxed differently and what it means for your tax bill.
If you are paid weekly and notice your final April payslip looks slightly different, you may have hit "week 53". It is one of payroll's quirks: a leftover day in the calendar that forces HMRC to tax your last payday of the year in a special way. Most people never notice, but it can leave a small tax bill that surfaces months later.
A tax year runs from 6 April to 5 April, which is 365 days, or 366 in a leap year. Divide 365 by 7 and you get 52 weeks plus one spare day. That spare day means roughly every five or six years a weekly payday lands exactly on 5 April, squeezing an extra payday into the year. Payroll calls this week 53.
The same logic applies to other cycles. Fortnightly payrolls can hit "week 54" (a 27th payment) and four-weekly payrolls "week 56" (a 14th payment). Monthly pay is immune because a year always contains exactly 12 calendar months.
Normally your tax is worked out on the cumulative basis: payroll tracks your total pay and total tax-free allowance for the year and reconciles them every payday. But there are only 52 weeks' worth of allowance in a standard code. When a 53rd payment appears, there is no 53rd slice of allowance left to give.
To avoid charging tax on the whole of that final payment, HMRC instructs employers to switch the last payment to the week 1 basis. This hands you one extra week's tax-free allowance, £242 in 2025/26 (the £12,570 Personal Allowance split across 52 weeks plus a bit), so the payment is not over-taxed at the moment you receive it.
Tom is paid £500 gross every Friday and has the standard 1257L tax code. In a week 53 year, his final Friday payday falls on 5 April 2026.
For weeks 1 to 52, payroll gives him roughly £242 tax-free each week and taxes the remaining £258 at 20%, about £51.60 of tax weekly. On his week 53 payment, payroll uses the week 1 basis and again applies £242 of tax-free allowance:
| Item | Amount |
|---|---|
| Week 53 gross pay | £500.00 |
| Tax-free slice (week 1 basis) | £242.00 |
| Taxable pay | £258.00 |
| Tax at 20% | £51.60 |
The catch is that Tom has now received 53 weekly allowances totalling about £12,826, more than the £12,570 he was entitled to. That extra £256 of untaxed income means he has underpaid roughly £51. HMRC will usually pick this up in a P800 reconciliation and recover it by adjusting his code the following year. Run your own weekly figures through the salary calculator to see the effect.
In almost all cases, nothing. Compliant payroll software detects a week 53 automatically and applies the week 1 basis without any input from you or your employer. The only thing to watch for is a P800 tax calculation after the tax year ends, which may show a small amount owing. This is normal and is spread over the following year through your tax code rather than demanded as a lump sum.
If you want to check the code being operated against your final April payslip, the check my tax code tool walks through what each part means.
Week 53 is not an error or a bonus payment; it is the calendar's rounding error, and HMRC has a specific rule to stop it over-taxing your last payday of the year.
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