Emergency tax refund estimator
Starting a job partway through the year on a month-1 emergency tax code often means overpaying, because it does not repay unused personal allowance from £12,570 built up before you started, under gov.uk's emergency tax code rules. This estimates the overpayment and roughly when HMRC refunds it.
Why do I overpay on an emergency code?
PAYE normally spreads the £12,570 personal allowance evenly across the year, about £1,048 a month, under gov.uk's guidance on tax codes. On a cumulative code, any allowance not used in earlier months is given back the moment pay starts. A month-1 emergency code does not do that: it treats each payslip in isolation, so the allowance from the months before work started simply goes unused while the code stays in place.
That is why starting a job partway through the year is the classic case. Someone who began work in the autumn after a gap had several months of allowance sitting idle, and the emergency code taxes them as though they had been earning at that rate all along. The tool compares the tax an emergency code takes with the tax estimated to be due on what has been earned, and the difference is the amount that should be refunded. If the code on your payslip looks unfamiliar, the payslip abbreviations guide explains what an emergency code and the other entries on the payslip mean.
How much emergency tax will I get back?
Suppose pay starts in October on £3,000 a month. Across the 6 months to the end of the tax year that comes to £18,000. The emergency code takes an estimated £391 a month, £2,343 in total. The estimated correct tax on £18,000 for the year is only £1,086, because the full personal allowance applies once earnings are looked at across the year. The estimated gap of £1,257 is refunded once HMRC moves the taxpayer onto a normal code, or after the tax year through a P800.
Common questions
What is an emergency tax code?
An emergency code, such as 1257L followed by M1, W1 or X, taxes each pay packet on its own rather than across the whole year. It is used when your employer does not have full details, for example when you start without a P45. It gives you the personal allowance, but only one month at a time.
Why do I overpay on an emergency code?
A month-1 code does not hand back the allowance built up in the months before you started. If you were not paid earlier in the tax year, that unused allowance is set aside while you stay on the emergency code, so the estimated tax taken is higher than the amount actually due for the year.
How much emergency tax will I get back?
In the example, starting in October on £3,000 a month, you overpay about £1,257. The figure depends on how many months of unused allowance you had before starting and your pay level.
When is the refund paid?
Once HMRC puts you on a normal cumulative code, usually within a month or two of getting your details, the overpaid tax is repaid automatically through your pay. If it is not corrected by the end of the tax year, HMRC works it out and sends a P800 tax calculation, then a refund.
Do I need to claim it?
Usually not. Most emergency-tax overpayments correct themselves through PAYE. If the tax year has ended and you have not had a refund, you can check and claim through your Personal Tax Account on gov.uk.
Sources & Rate Verification
Rates verified against official statutory guidance on 6 September 2026.