WageW1/M1 Tax Code — What It Means
An emergency, non-cumulative code (Week 1 / Month 1) where each pay period is taxed on its own rather than across your year-to-date pay.
How W1/M1 changes your pay on a £30,000 salary
| Code | Income tax / year | Per month | Take-home / month* |
|---|---|---|---|
| Standard 1257L | £3,486 | £291 | £2,210 |
| W1/M1 | An emergency (non-cumulative) code taxes each pay period in isolation; on a stable salary the yearly result matches 1257L, but it can over- or under-deduct mid-year until corrected. | ||
*Take-home per month here reflects income tax only; National Insurance and any student loan or pension are separate.
Why you might have the W1/M1 code
- You have recently started a new job and HMRC does not yet have your full details.
- You moved from self-employment to an employer, or started getting company benefits or the State Pension.
- Your P45 was not available, so your employer applied an emergency code.
How to fix a wrong code
Emergency codes are temporary. Once HMRC has your correct details it usually issues the right cumulative code, and any over- or underpayment is then adjusted.
Related codes: 0T · BR · 1257L · All tax codes
General information, not advice. Estimates assume the standard 1257L tax code and typical circumstances; your payslip may differ by a pound or two because HMRC payroll software truncates at each step. Verify with HMRC or an accountant for any decision. WageReckon stores no salary data - the calculators run in your browser.
Rates for the 2026-27 tax year, current as of 24 July 2026. Source: HMRC (gov.uk). Contains public sector information licensed under the Open Government Licence v3.0. Source: HMRC / gov.uk. See how we calculate.