Emergency Tax Code in the UK: What It Means & How to Fix It
If you start a new job without providing a P45, or if HMRC does not have up-to-date information about your employment, your employer will use an emergency tax code. Emergency codes almost always result in overpayment of income tax during the period they apply.
What triggers an emergency tax code?
- Starting a new job without a P45 from your previous employer
- Starting your first ever job (no employment history on HMRC records)
- Returning to work after a gap and not having a current P45
- HMRC not receiving information from your employer in time
- Receiving a pension for the first time
Common emergency tax codes
- 1257L W1 or 1257L M1: The most common emergency code. You receive your standard Personal Allowance but it is calculated on a week-by-week (W1) or month-by-month (M1) basis rather than cumulatively across the year. This means if you received no income in April, HMRC does not credit that unused allowance against future months.
- BR: Basic Rate — all income taxed at 20% with no Personal Allowance. Used when HMRC believes this is a second job, or when no information is available.
- OT: No Personal Allowance at all, taxed at the appropriate rate for each band. Often used when insufficient information exists about your personal circumstances.
How W1/M1 leads to overpayment
Under a cumulative code, unused Personal Allowance from earlier in the year is applied to later months. Under a W1/M1 code, each pay period is treated as if it were the first — no cumulation, no catch-up. If you joined a company in September and were on 1257L M1, you would not receive credit for the six months of unused allowance from April to August.
How to fix an emergency tax code
- Give your P45 to your new employer. This is the fastest fix. Your employer updates your code and the cumulative calculation resets correctly.
- Complete a Starter Checklist. If you do not have a P45, fill in the form your employer should give you. It asks about your previous employment and income, allowing HMRC to assign the right code.
- Contact HMRC directly. Call 0300 200 3300 with your National Insurance number and employment details. HMRC will update your tax code, which is then sent to your employer.
Will you get your overpaid tax back?
Yes. Once your correct code is applied, your employer will recalculate tax cumulatively and refund the overpayment through your next payslip. If the year ends before the code is corrected, HMRC will identify the overpayment during the end-of-year reconciliation and issue a P800 letter.
Frequently asked questions
How long does it take to fix an emergency tax code?
If you give a P45 to your new employer, the correction typically appears in your next payslip. If HMRC needs to update the code directly, it usually takes one to six weeks.
Can I check my tax code online?
Yes. Your current tax code is visible in your Personal Tax Account at gov.uk/personal-tax-account. You can also find it on your payslip or the P2 notice HMRC sends after each code change.