What is an emergency tax code?
Your PAYE tax code tells your employer or pension provider how much Income Tax to deduct from your pay or pension.
An emergency tax code can be used where HMRC or your employer does not yet have all of the information needed to operate your normal tax code.
Emergency tax does not mean there is a special emergency tax rate. It means your tax code is being operated using a temporary calculation basis until the appropriate PAYE information is available.
What do W1, M1 and X mean on a tax code?
GOV.UK identifies W1, M1 and X as emergency tax code markers. They indicate that the PAYE calculation is being operated on a non-cumulative basis.
| Code marker | What it means |
|---|---|
| W1 | Week 1 basis. Tax is calculated using the allowance available for that pay period rather than recalculating the whole tax year cumulatively. |
| M1 | Month 1 basis. The calculation is similarly based on the current monthly pay period rather than the year to date. |
| X | Another marker HMRC uses to show that a tax code is being operated on an emergency basis. |
For the 2026/27 tax year, HMRC's employer payroll guidance states that the standard emergency code is 1257L. Whether 1257L is actually being used as an emergency code depends on how it is operated and whether an emergency marker such as W1, M1 or X is attached.
Why might you be put on an emergency tax code?
You've started a new job
Your new employer may not yet have enough information about your earlier pay and tax for the year.
You do not have a P45
If you cannot provide a P45, your employer needs other information to determine the appropriate starter tax code.
Your circumstances changed
Changes to PAYE information can sometimes result in a temporary emergency code while HMRC updates your record.
New taxable benefits or pension
HMRC says an emergency code may also be used when you start receiving certain company benefits or the State Pension.
How does emergency tax affect your pay?
Under the normal cumulative PAYE system, the payroll calculation can take account of taxable pay, tax already deducted and available allowances earlier in the tax year.
An emergency W1 or M1 basis instead broadly considers the current weekly or monthly pay period in isolation.
Earlier unused allowance may not be reflected immediately
Because a non-cumulative code does not recalculate the whole year in the usual cumulative way, the tax taken in a particular pay period can differ from the amount that would be due after your full PAYE position is updated.
An emergency code does not automatically mean that you are overpaying tax. Whether too much or too little has actually been deducted depends on your income, previous pay, tax already paid and wider circumstances.
Why are emergency tax codes common when starting a new job?
When you start employment, your new employer needs information about your PAYE position to put you on payroll correctly.
A P45 from your previous employer normally provides useful information about your tax code, taxable pay and Income Tax paid earlier in the tax year.
If the appropriate information is not available when payroll is first processed, an emergency or other starter code may need to be used.
What happens if you start a job without a P45?
GOV.UK provides a Starter Checklist for employees who begin a new job without a P45. The information given on that checklist helps the employer work out the starter declaration and tax code to use.
It is therefore important to provide accurate information about your employment position rather than simply leaving the employer without the details needed for payroll.
We will cover this document in more detail in our P45 Explained Guide .
Can emergency tax make you pay too much tax?
It can result in too much tax being deducted in some circumstances, but this is not automatic.
If HMRC later receives the information needed to correct your PAYE record, your tax code can be updated. Where HMRC has all the necessary income details, it can work out the difference between the tax you have paid and the amount you should have paid.
If you think an emergency code has resulted in an overpayment, also read our Overpaid Tax Guide .
What should you do if your emergency tax code looks wrong?
Do not assume that your employer can simply choose whichever tax code you want. PAYE codes are operated using the information available to the employer and instructions received from HMRC.
Check your payslip
Look at the tax code being used and check whether it carries W1, M1 or X.
Check your employment information
Confirm that your employer received your P45 or the correct Starter Checklist information where appropriate.
Check your tax code with HMRC
GOV.UK provides online services for checking what your tax code means and updating employment details where your code appears incorrect.
Review any overpayment
If too much tax has been deducted, the correction or refund route depends on whether the issue is corrected through payroll or identified later by HMRC.
This depends on why it was issued. HMRC's current guidance says that where an emergency code is used because you have started receiving company benefits or the State Pension, it may remain until the end of the tax year. In other circumstances, a code may be updated sooner when HMRC receives the information needed to change it.
Reviewed & Updated
11 August 2026
2026/27
GO TAX REFUNDS
HM Revenue & Customs / GOV.UK
Tax codes depend on individual PAYE circumstances and can change during the tax year. This guide provides general information and should be checked alongside your current HMRC tax code and employment records.
Emergency Tax Code FAQs
Is 1257L always an emergency tax code?
No. HMRC says 1257L is an emergency tax code when it is followed by W1, M1 or X. The code 1257L can also be used on a normal cumulative basis.
What does 1257L M1 mean?
M1 means Month 1. The code is being operated on an emergency, non-cumulative basis, so the PAYE calculation broadly treats the current month independently rather than recalculating your whole tax year.
What does 1257L W1 mean?
W1 means Week 1. It is an emergency basis that broadly calculates tax using the current weekly pay period rather than carrying out the normal cumulative year-to-date calculation.
Will emergency tax be refunded automatically?
Sometimes an updated cumulative code can correct the PAYE position through payroll, while other overpayments may be dealt with by HMRC later. Whether a refund is due depends on your overall Income Tax position.
Why am I on emergency tax after changing jobs?
One common reason is that your new employer or HMRC does not yet have all of the PAYE information needed from your previous employment. Providing your P45 or accurate Starter Checklist information can help ensure the right starter information is used.
Can my employer change my emergency tax code?
Employers must operate PAYE using the appropriate payroll information and HMRC instructions. If you believe your code is wrong, check your employment details and use HMRC's tax code services rather than asking an employer simply to choose a different code.
Can an emergency tax code cause an overpayment?
Potentially. A non-cumulative calculation can sometimes result in more tax being deducted than is ultimately due. The final position depends on your total income, previous pay, tax already paid and allowances for the year.
HMRC & GOV.UK Sources
This guide is reviewed against current HMRC guidance on tax codes, new starters and emergency PAYE codes.
Think your emergency tax code has caused an overpayment?
Go Tax Refunds can help review your PAYE records, employment history, tax codes and Income Tax deductions to establish whether you may have paid too much tax.
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