Emergency tax codes: why they happen and what to do

Scope: This guide is for UK employees and pension recipients whose PAYE code ends in W1, M1 or X, or whose payslip shows NONCUM, during the 2026 to 2027 tax year.

The short answer

You are on an emergency tax code if the code ends in W1, M1 or X. Depending on the employer’s payroll software, the payslip may instead show NONCUM. Instead of using total pay and tax from the start of the tax year, payroll works out tax from the current week or month alone. This can be a sensible temporary calculation when HMRC or a new employer does not yet have complete information, but it can result in too much or too little tax being deducted.

If you have just started a job, give the employer your P45. If you do not have one, complete the starter information requested by the employer. HMRC normally updates the code after receiving the relevant details; its guidance says this can take up to 35 days from starting the job.

How to recognise an emergency code

Look at the complete code on the payslip or pension statement, including any suffix or NONCUM marker:

• 1257L W1 means week 1 treatment;
• 1257L M1 means month 1 treatment;
• a code ending X is used where pay dates vary; and
• NONCUM may appear instead, depending on the employer’s payroll software; and
• Scottish or Welsh codes can also carry an emergency marker, for example S875L M1 or C663L X.

The number and main letter still have their normal coding functions. The W1, M1, X or NONCUM marker shows that the operation is non-cumulative.

How emergency treatment changes the calculation

PAYE normally takes account of total taxable pay and tax already deducted in the tax year. Under an emergency code, the calculation looks only at the current pay period and treats that level of pay as though it continues through the year.

Worked scenario

Someone starts a monthly-paid job without a P45 and payroll uses 1257L M1. Their September deduction uses one month’s share of the coded allowance and tax bands, without automatically recalculating earlier pay and tax from April to August. When HMRC supplies a cumulative code, payroll may be able to reconcile the year-to-date position through a later payment.

This scenario explains the mechanism. The actual deduction depends on pay, the full code, earlier income and HMRC’s later instruction.

Why an emergency code may appear

Common situations in HMRC’s guidance include:

• starting a job when the new employer does not have previous income and tax details;
• beginning to receive a company benefit; or
• beginning to receive the State Pension.

The presence of an emergency code does not by itself prove that payroll has made an error. It means the code is using a temporary or non-cumulative basis that should be checked against the current facts.

What to do after starting a job

1. Give the employer your P45. It provides previous pay and tax details. If the former employer did not provide it, ask for it.
2. Complete the starter information accurately if there is no P45. Do not guess whether this is your first or only job.
3. Check HMRC’s record. Use the current-year Income Tax service to check the job, estimated income, benefits and code.
4. Allow for the normal update process. HMRC says a new-job update can take up to 35 days from the start date.
5. Act if it remains wrong. If more than 35 days have passed, update the incorrect details through HMRC or contact HMRC if you cannot use the service.
6. Check the next payslip. Confirm both the new code and the year-to-date pay and tax figures.

Company benefits or State Pension

HMRC says an emergency code can also be used when a company benefit or State Pension starts. Check that the item and its amount appear in HMRC’s record. If they do not, update the details. In these cases HMRC’s guidance says the emergency code may remain until the end of the tax year, with a non-emergency code then used in the new year.

If too much or too little tax has been taken

A corrected cumulative code may adjust deductions through a later payroll run. Do not assume every overpayment will be corrected immediately or that every difference is a refund: check the new coding notice and payslip.

If tax still appears overpaid, use HMRC’s official route to identify the correct claim process. When the related UK Tax Hero guide is live, see how to check the appropriate tax-refund route.

Common mistakes

• Looking only at 1257L and missing the W1, M1, X or NONCUM marker.
• Assuming the emergency code means no Personal Allowance has been given.
• Waiting indefinitely without checking whether HMRC has the correct job or pension information.
• Asking payroll to choose a code that HMRC has not supplied.
• Treating a single month’s difference as proof of the final annual underpayment or overpayment.

What to do next

• Check the exact suffix on the latest payslip.
• Supply the P45 or starter information.
• Compare HMRC’s job, income, benefit and pension data with your records.
• Recheck after the update period and retain the coding notice and payslips.
• Read how to interpret the rest of a PAYE tax code.