Emergency Tax Codes
What does the 1257L W1 tax code mean? (And how to get off it)
If your new payslip says 1257L W1 (or M1, or X), do not ignore it. You have been placed on a non-cumulative emergency tax code. While it sounds terrifying, fixing it is straightforward once you know how HMRC's payroll system actually works.
The standard tax code for almost everyone in the UK for the 2026/27 tax year is 1257L. This code gives you a tax-free Personal Allowance of £12,570 for the year.
However, if your payslip shows 1257L W1, 1257L M1, or 1257L X, the payroll software has essentially hit the panic button. You are on an emergency tax code.
What does W1 or M1 actually mean?
The letters W1 (Week 1) or M1 (Month 1) mean your tax is being calculated on a non-cumulative basis.
Normally, the UK PAYE system looks at your total earnings for the entire year to date to calculate exactly how much tax you should pay. It takes your £12,570 tax-free allowance and spreads it evenly across the year.
When you have a W1 or M1 suffix, HMRC is telling your employer: "We don't know how much this person earned in their previous jobs this year, so just treat this single week (or month) in isolation."
Your employer will divide your £12,570 allowance by 12 (£1,047.50) and apply exactly that much tax-free allowance to your current payslip. They will completely ignore any tax you paid, or any allowance you didn't use, in previous months.
Are you overpaying tax?
If you were unemployed for a few months before starting this job, a W1/M1 code guarantees you are overpaying tax, because you aren't being credited for the months of unused tax-free allowance.
Check Emergency Tax Guide →Why was I put on an emergency tax code?
This happens almost exclusively when you start a new job and your new employer's payroll department doesn't have enough information about your tax history. The three main culprits are:
- You didn't hand in a P45: If you didn't give your new employer a P45 from your previous job, they don't know how much you earned earlier in the tax year.
- You didn't fill out a Starter Checklist: If you don't have a P45 (e.g., this is your first job), you must fill out a HMRC Starter Checklist. If you don't, HR defaults to W1/M1.
- HMRC data delay: Sometimes you do everything right, but HMRC's computers haven't sent the electronic coding notice to your employer's payroll software yet.
How to fix a 1257L W1 / M1 tax code
Getting off an emergency tax code and back onto a standard cumulative code (just 1257L without the letters) is very easy, but it requires action.
Step 1: Check if you have a P45
If you recently left an old job, they legally must provide you with a P45. If you have it, hand Parts 2 and 3 to your new HR department immediately. Next time they run payroll, the software will automatically remove the W1/M1 suffix and recalculate your tax.
Step 2: Fill out a New Starter Checklist
If you don't have a P45, go to Gov.uk, search for "Starter Checklist", print it out, fill it in (make sure you select Statement A if this is your first job since April 6th), and hand it to your manager. This is the legal replacement for a P45.
Step 3: Wait for the tax rebate
Once your tax code is corrected to a standard 1257L, the PAYE system switches back to "cumulative" mode. The payroll software will instantly look back at your earnings for the whole year. If you overpaid tax while on the emergency W1/M1 code, it will automatically refund you the money on your next payslip. (This will show up as a negative tax figure).
Frequently Asked Questions
Is 1257L W1 the same as the 0T tax code?
No. 1257L W1 still gives you a tax-free allowance (£1,047 a month). The 0T tax code gives you absolutely zero tax-free allowance, meaning you are taxed 20% on every single penny you earn. If you are on 0T, you are losing significantly more money.
My employer says they can't change it. What do I do?
Employers are legally restricted from changing tax codes manually without a P45, a Starter Checklist, or a direct electronic notice (P6) from HMRC. If your employer is refusing to accept a Starter Checklist, you must call HMRC directly on 0300 200 3300. Tell them you are on a W1 code, provide your estimated annual salary, and HMRC will send a direct electronic command to your employer's payroll software to fix it.
If I don't fix it, will I lose the money forever?
No. If you reach the end of the tax year (April 5th) and you are still on a W1/M1 code, HMRC's computers will automatically sweep your account, realize you overpaid, and send you a P800 letter with a tax refund cheque in the post around June or July.