Emergency tax codes: W1, M1 and X
You're on an emergency tax code if it ends in W1, M1 or X, or your payslip says NONCUM. Instead of looking at your pay for the whole tax year so far, each payment is taxed on its own, as if you were paid that amount every week or month. It's usually temporary, often used when you start a new job before your employer has your P45.
Compare with what you'd take home once your normal code is in place.
See take-home on 1257LWhat W1, M1 and X mean
| Ending | Used when |
|---|---|
| W1 | You're paid weekly, for example 1257L W1 |
| M1 | You're paid monthly, for example 1257L M1 |
| X | Your pay dates vary |
Why it can cost you
Normally PAYE is cumulative: it looks at all your pay and tax since 6 April, so an underpayment in one month is caught up and an overpayment is refunded. On W1 or M1, each payment stands alone, so nothing earlier is taken into account.
Example: paid £3,000 in month 6 on 1257L M1, the tax is £390.20, exactly as if it were month 1. On cumulative 1257L, with the same pay every month so far, it would be £391.00, because the year-to-date figures are used.
How to get off an emergency code
- Give your new employer your P45 from your last job, if you have it.
- HMRC usually sends an updated code once it has your details, which GOV.UK says can take up to 35 days.
- If it's still wrong after that, update your details through your HMRC online account.
Questions
Do I get my money back after an emergency tax code?
If you paid too much, it's usually refunded through your pay once you're on a normal cumulative code, or by HMRC after the tax year.
Is 1257L M1 an emergency tax code?
Yes. Any code ending in W1, M1 or X is on an emergency (non-cumulative) basis.
Sources
- GOV.UK — Tax codes: emergency tax codes
- HMRC — Specification for PAYE Tax Table Routines, version 24.0
Official sources checked 24 September 2026. This guide explains how pay documents work; it is not tax or legal advice.