Emergency Tax Code: What It Is and How to Fix It Fast
An emergency tax code is applied by your employer when HMRC does not have enough information to issue a full tax code in time for your first payday. The most common emergency codes are 1257L W1 (weekly pay) and 1257L M1 (monthly pay). Scotland uses S1257L W1 and S1257L M1.
The W1/M1 suffix is the problem. It means the code is applied on a non-cumulative basis — HMRC calculates tax only on that pay period's income, without considering what you have earned or paid so far in the tax year. This can cause significant overpayment if your income is irregular or if you have unused Personal Allowance earlier in the year.
How much tax does an emergency code deduct?
On a standard emergency code like 1257L M1, your tax for that month is calculated as if you receive the same salary every month with a monthly personal allowance (£12,570 ÷ 12 = £1,047.50). This can result in overpayment if:
- You started the job partway through the tax year and have unused allowance from months without income
- You received a large one-off payment (bonus, back pay) that inflates one month's tax
- Your income varies significantly month to month
Example: You start a £36,000/year job in November (month 8 of the tax year, April = month 1). Under a correct cumulative code, HMRC would account for 7 months of unused allowance. Under M1 emergency code, each month is calculated independently — you may pay several hundred pounds more tax over the year.
BR as an emergency code
In some cases, employers default to BR (or SBR in Scotland) as an emergency measure. BR taxes all income at 20% with no allowance whatsoever — potentially more costly than 1257L M1 if your income is below £12,570. A £10,000 annual income on BR costs £2,000 in tax; on 1257L M1 it costs nothing (below the annual allowance).
How to fix an emergency tax code: step by step
- Give your employer your P45 from your previous job. This is the fastest fix — your employer uses the leaving code and pay figures to request the correct code from HMRC.
- Complete a starter checklist (formerly P46). If you do not have a P45, fill in the starter checklist your employer provides, stating whether this is your only job, a second job, or whether you are coming from unemployment or education.
- Contact HMRC directly on 0300 200 3300 or via your Personal Tax Account at gov.uk. HMRC can issue the correct code to your employer within days.
- Wait for automatic correction. HMRC updates codes automatically at the start of each tax year and at various points during the year. The incorrect tax paid under an emergency code will typically be refunded by year end through a P800 calculation.
When will I get my refund?
HMRC issues P800 tax calculations after the tax year ends (April). If you have overpaid tax through an emergency code, you should receive a P800 letter by October/November, with a refund issued shortly after. For faster resolution, claiming via your Personal Tax Account (R40 form for savings/other income; online claim for PAYE) can speed up the process.
Frequently asked questions
What is an emergency tax code?
An emergency tax code (typically 1257L W1 or 1257L M1) calculates tax on a non-cumulative basis — each pay period is taxed independently without reference to the rest of the year. This can cause over- or under-payment and should be resolved as soon as possible.
How long does emergency tax last?
Until HMRC issues your correct code, which typically happens after your employer submits payroll information. This usually takes 4–8 weeks but can be faster if you contact HMRC directly or provide a P45.
Am I owed money back from emergency tax?
Possibly. If you started work mid-year and have months of unused Personal Allowance, the cumulative code will be more beneficial. HMRC will calculate this at year end and issue a refund if you have overpaid.
What is the difference between 1257L W1 and 1257L M1?
W1 is used for weekly payrolls; M1 is for monthly payrolls. Both are non-cumulative emergency codes. The tax calculation is the same in principle — just applied weekly or monthly.