What tax code Emergency tax (W1/M1/X) actually means
Usually a 1257L code with a W1, M1 or X suffix — each payday taxed in isolation until HMRC confirms your details.
"Emergency tax" almost always means your tax code has a W1, M1 or X suffix — typically 1257L W1 or 1257L M1. Each pay period is calculated in isolation with one week's or month's slice of the £12,570 allowance, and no look-back at the year so far. You still get an allowance, but you can temporarily overpay — especially if you had a gap between jobs. It fixes itself once HMRC sends your employer a cumulative code.
- Personal allowance
- £12,570 (applied one period at a time)
- Applies in
- All UK regions
- Calculation
- Non-cumulative
Non-cumulative code — results assume consistent weekly earnings
See this salary on a different tax code → (opens the main calculator pre-filled with Emergency tax (W1/M1/X))
What does Emergency tax (W1/M1/X) mean?
When an employer doesn't have enough information to tax you accurately — no P45, no completed starter checklist — they apply an emergency code. You still get the standard £12,570 allowance, but only in per-period slices (£1,047.50 a month), and the payroll never looks back at what you've already earned or paid this year.
That look-back is what normally protects you. On a cumulative code, if you start a job in October having not worked since April, your unused allowance from April–September is applied immediately and your first payslips are taxed lightly or not at all. On an emergency code that unused allowance sits idle — so you overpay until the code is corrected.
The fix is administrative, not financial: give your employer your P45, or complete the starter checklist so HMRC can issue the right code. You can also update your details in your personal tax account. Once a cumulative code arrives, your next payslip automatically refunds any in-year overpayment.
When you’ll see Emergency tax (W1/M1/X)
- You started a new job without a P45 from your previous employer.
- You moved from self-employment to employment.
- You started your first ever job mid-year.
- You began receiving a workplace or private pension.
- You started a second job and HMRC hasn't allocated your allowance yet.
Emergency tax (W1/M1/X) vs other common codes
| Code | Personal allowance | How income is taxed |
|---|---|---|
| 1257L | £12,570 | Standard bands after the allowance |
| BR | £0 | Flat 20% on everything |
| 0T | £0 | Normal bands from the first pound |
| D0 | £0 | Flat 40% on everything |
Emergency tax (W1/M1/X) questions, answered
Related tax codes
1257L
The standard code for 2025/26 — a £12,570 tax-free personal allowance, applied evenly across the year.
Decode itBR
Basic Rate on everything: 20% from the first pound, no personal allowance — normal for second jobs and pensions.
Decode it0T
Zero allowance, but normal bands: 20%, then 40%, then 45% — from the very first pound you earn.
Decode itScottish tax codes (S)
An S at the front of your code means Scottish rates: six bands from 19% to 48% in 2025/26.
Decode itK codes
The code that works in reverse: instead of tax-free pay, a K code adds to your taxable income.
Decode itW1 / M1 / X
Suffixes, not codes: W1 (weekly), M1 (monthly) and X switch off the year-to-date calculation.
Decode itNot sure this is the right code for you?
Don’t take our word for it — HMRC holds the code they’ve actually issued for each of your jobs, and you can check it in two minutes.
Sources: tax codes — gov.uk · income tax rates · Scottish income tax