Answers · UK 2025/26
What is an emergency tax code and how do I fix it?
An emergency tax code (W1, M1, X or noncumulative) is applied when HMRC has no full income history — typically when starting a new job without a P45. It taxes each pay period in isolation, often resulting in initial overpayment. HMRC usually fixes it within 1-3 pay cycles automatically.
Full answer
UK emergency tax codes 2025/26. Three common emergency code formats: 1257L W1 (week 1 basis), 1257L M1 (month 1 basis), 1257L X (non-cumulative). All mean the same thing: each pay period treated in isolation rather than cumulatively. When applied: starting a new job without a P45; receiving multiple sources of income; HMRC has insufficient data; first job. Why this causes overpayment: a cumulative code spreads the £12,570 Personal Allowance evenly across the year (£1,047/month tax-free). An emergency code only allows £1,047 in the current period — but if you started mid-year, you missed previous months' allowances that you're due. Example: start job in October on £40,000 (£3,333/month). Emergency M1: each month you get £1,047 tax-free, but you should have access to your unused 6 months' worth (~£6,285). You overpay by ~£1,257 over 3-4 months until HMRC corrects. How to fix: (1) submit your P45 from your last job (if you have one); (2) sign in to gov.uk/personal-tax-account and check what HMRC has; (3) call HMRC 0300 200 3300 — they can update your code over phone; (4) wait — HMRC usually corrects within 2-3 pay cycles automatically via "annual review". After correction, you receive overpaid tax back in your next salary through a cumulative code applying retrospectively.
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This answer is informational only and does not constitute financial, tax or legal advice. Figures are for the 2025/26 UK tax year. See our methodology and sources.