If you have started a new job and your first payslip shows significantly less take-home pay than expected, you may have been put on an emergency tax code. This is temporary, fixable, and any overpaid tax will be refunded — but it can be alarming when you first see it. This guide explains why emergency codes happen, how much extra tax they cost you, and exactly what to do to resolve it. The standard tax code for 26-27 is 1257L, representing a Personal Allowance of £12,579.[1]
What is an emergency tax code?
An emergency tax code is applied when your employer does not have enough information to calculate your tax correctly. The most common emergency codes for 26-27 are 1257L W1 (for weekly-paid employees) and 1257L M1 (for monthly-paid). The code number (1257) is the same as the standard code — it still gives you the correct monthly allowance. The critical difference is the W1/M1 suffix.
The W1 (Week 1) or M1 (Month 1) suffix means “non-cumulative” calculation. Instead of taking into account your earnings and tax paid since the start of the tax year (6 April), each pay period is treated in isolation. You receive exactly 1/12th of your Personal Allowance each month (£1,048) regardless of what happened in previous months. Under a normal cumulative code, if you joined mid-year you would receive the accumulated unused allowance from earlier months in one go.
Another emergency code is 0T W1/M1 — this is more aggressive and means no Personal Allowance at all. Your entire salary is taxed using all bands (20%, 40%, 45%) starting from the first pound. This happens when HMRC has no information about you at all and is less common than 1257L W1/M1.
Why has my employer used an emergency tax code?
Your employer must use an emergency code when they do not have your P45 from your previous employer and HMRC has not yet issued them a tax code for you. Common scenarios:
- New job without a P45: your previous employer was slow to issue it, or this is your first job of the tax year.
- First job ever: HMRC has no record of you as an employee, so no code has been pre-assigned.
- Returning from a career break, travel, or self-employment: no recent P45 exists and HMRC needs to assess your situation.
- Starter Checklist not completed: your employer should give you a Starter Checklist if you do not have a P45 — if this is not submitted to HMRC, the code cannot be corrected.
How much extra tax does an emergency code cost me?
The extra tax depends on when in the tax year you start. The later you start, the more unused cumulative allowance you miss out on under a non-cumulative code. For a basic rate taxpayer:
- Start in Month 2 (May): miss 1 month = £1,048 allowance, overpay ≈ £210
- Start in Month 4 (July): miss 3 months = £3,144 allowance, overpay ≈ £629
- Start in Month 7 (October): miss 6 months = £6,288 allowance, overpay ≈ £1258
- Start in Month 10 (January): miss 9 months = £9,432 allowance, overpay ≈ £1886
This assumes you had no other income earlier in the tax year. If you did work elsewhere and had a P45, the overpayment may be smaller because HMRC will account for tax already paid. For a 0T code with no allowance at all, the overpayment is even larger because you lose the full monthly allowance of £1,048 on every pay period until it is corrected.
How do I fix my emergency tax code?
The fix depends on your situation:
- If you have a P45 from your previous employer: give it to your new employer immediately. They submit the details to HMRC and your correct cumulative code will be issued, usually within the next pay period. Overpaid tax is refunded automatically in that payslip.
- If you do not have a P45: ask your employer for a Starter Checklist (formerly P46). Complete it honestly — particularly the statement about whether this is your first job of the year or if you have another job. Your employer submits this to HMRC.
- If you have already submitted a Starter Checklist and nothing has changed after 4 weeks: contact HMRC directly on 0300 200 3300 (Income Tax helpline) or update your details through your Personal Tax Account online at gov.uk. They can issue the correct code immediately.
Once your correct cumulative code is issued (usually 1257Lwithout the W1/M1 suffix), your employer recalculates your year-to-date tax position. All overpaid tax is refunded in your next payslip as a larger-than-normal net pay figure. You do not need to claim a separate refund.
What if the tax year ends and I am still on an emergency code?
If the tax year ends (5 April) before your code is corrected, you will have overpaid tax for the year. In this case:
- HMRC usually reconciles your tax position automatically after the year ends (by July/August) and sends a P800 tax calculation showing how much you are owed.
- You can claim a refund online through your Personal Tax Account if the automatic reconciliation has not happened by September.
- Alternatively, HMRC may adjust your tax code for the following year to give you the overpaid amount back gradually through reduced monthly deductions.
How can I see the difference an emergency code makes?
Use the income tax calculator with your salary to see what your monthly take-home should be under the standard code 1257L. Compare this against your actual payslip to quantify exactly how much extra you are paying. The difference is your overpayment, which will be refunded once the correct code is applied.
For more on how tax codes work and what the letters mean, see our tax codes explained guide.
Sources
- HMRC — Emergency tax codes. What emergency tax codes are, when they are used, and how to resolve them. Accessed July 2026.
- HMRC — Tax codes. Standard code 1257L for 26-27, representing Personal Allowance of £12,579. Accessed July 2026.
- HMRC — Income Tax rates and Personal Allowances. Basic rate 20%, higher rate 40%. Accessed July 2026.