W1 M1 tax code meaning: what emergency tax is and how it ends

A W1, M1 or X suffix means tax is worked out for each pay period on its own. This is what people call emergency tax, and it is meant to be temporary.

Updated 9 October 2026. Facts checked against GOV.UK and legislation.gov.uk on 9 October 2026.

What the suffix means

GOV.UK lists three suffixes. W1 is for weekly pay, M1 is for monthly pay, and X is used where pay dates vary. Examples on GOV.UK include 1257L W1, S875L M1 and C663L X. Depending on your employer’s payroll software, you may also see NONCUM on the payslip.

The effect is that you are taxed as if you were paid that week’s or that month’s amount in every period. GOV.UK warns that this could mean you pay the wrong amount of tax.

What “emergency tax” really means

Emergency tax is not a separate rate. The same bands and rates apply as for any other code (in England, Wales and Northern Ireland, 20%, 40% and 45%; Scotland has its own). What changes is how your allowance is applied. A cumulative code works on your total pay since 6 April. A non-cumulative code works on each period on its own, so the tax on one pay does not take account of the rest of the year.

That is why the total for the year can come out wrong in either direction. GOV.UK says emergency tax is usually temporary, and it is used when your new employer does not have your previous income and tax details.

Where the code comes from

If you do not have a P45, the starter checklist decides the code. Statement A gives the current personal allowance on a cumulative basis, which is 1257L. Statement B gives the current personal allowance on a week 1 or month 1 basis, which is 1257L W1 or M1. Statement C gives BR.

Statement B covers a job that is now your only job. Since 6 April you have had another job (which has now ended) and you do not have a P45, or you have received taxable Jobseeker’s Allowance, Employment and Support Allowance or Incapacity Benefit. The regulations say that in this case the employer must deduct tax on a non-cumulative basis, using the emergency code, until your code is issued.

1257L W1 and 0T

Both codes, when given to a new starter, work on a non-cumulative basis, but they treat the allowance differently. 1257L W1 gives you about £242 of tax-free pay each week (one fifty-second of the allowance). Pay below that in a week is not taxed. 0T gives no allowance at all, so tax starts from the first pound.

The 1257L W1 result comes from statement B. The 0T result comes from having no checklist at all. The starter checklist is the employee’s way of avoiding the 0T result, because it tells the employer which allowance to use.

The 0T tax code: no tax-free allowance, with pay taxed through the bands

How it is resolved

HMRC usually updates the code once it has details from your new and previous employers. The steps to get off an emergency code are set out below.

A code for a new job is usually temporary and changes once HMRC has your details. GOV.UK says you stay on an emergency code until the end of the tax year if you have started to get company benefits or the State Pension, and until you have paid the correct tax for the year if you underpaid.
When a new code arrives after an overpayment, the correction comes through your pay. The emergency tax refund guide explains how and when.

Emergency tax refunds: how overpaid tax comes back through your pay or a P800

How to get off an emergency code

HMRC can take up to 35 days to send a new code. These steps give HMRC and your new employer the details they need, so check them first:

Give your new employer Parts 2 and 3 of your P45, and keep Part 1A.
If you have no P45 and have not been paid yet, complete the starter checklist instead. Use the online form, or the PDF if you cannot use it.
Check your code in the HMRC app or your personal tax account. It shows your current-year Income Tax, including your tax code.
If it has not changed after 35 days, contact HMRC.

What to check on your payslip

Check the suffix first. W1 is for weekly pay and M1 is for monthly pay, so the suffix should match how you are paid.

The number. 1257L means the standard allowance applies, and 0T means no allowance applies.
Your starter checklist statement, and whether you gave your employer a P45 from your previous job.
Whether you have a second job or pension. If you do, statement C may apply, and a BR code may be the right one.

If the year-end figures look wrong

After the tax year ends on 5 April, HMRC checks the tax you paid. If it finds you paid too much or too little, it sends a P800 tax calculation letter. The guide on emergency tax refunds covers what to do with that letter.

Emergency tax refunds: how overpaid tax comes back through your pay or a P800

Why irregular pay makes it worse

Emergency codes work best with steady pay. If your pay is the same each week or each month, the tax taken in each period is close to the right amount for the year. Irregular shifts make it less accurate, because a busy period is taxed as though it will repeat in every period.

Seasonal and irregular work is therefore worth checking early, on the first two or three payslips, rather than waiting for the end of the year.

Related guides

Sources

This is an estimate, not financial or tax advice. Your payslip is the final figure.