UK tax codes · 2026/27 tax year

What does tax code 1257L M1 mean?

1257L M1 usually means your employer is using the standard tax-free allowance, but calculates tax for this month only instead of taking earlier pay and tax into account.

The short answer

1257L is the standard tax code for most people with one job. M1 means “month 1”, an emergency or non-cumulative tax basis. It is often temporary when a new employer does not yet have enough information about your earlier pay.

Breaking down 1257L M1

1257: Usually gives a tax-free allowance of £12,570 for the 2026/27 tax year.
L: Normally means you are entitled to the standard Personal Allowance.
M1: Means your Income Tax is worked out using this month's pay only. Previous pay and tax from the current tax year are not included in that calculation.

How it differs from ordinary 1257L

With an ordinary cumulative 1257L code, payroll considers your taxable pay and Income Tax paid so far in the tax year. It can correct an earlier overpayment or underpayment over later payslips. With 1257L M1, each month is treated separately, so that correction does not happen through the usual cumulative calculation.

This can mean your tax is temporarily higher or lower than it would be on a cumulative code. It does not automatically mean your employer has made a mistake.

Why you may have this code

You have recently started a new job and your employer does not yet have your P45 details.
You completed a starter checklist and HMRC is still matching your current employment with earlier records.
HMRC has issued a temporary non-cumulative code while it reviews your circumstances.

What to do next

Check that your employer has your P45. If you do not have one, make sure you completed the starter checklist accurately.
Check your tax code in your HMRC Personal Tax Account and compare it with the code on your payslip.
Look at your next payslip. HMRC may replace an emergency code once it has the required information.
If you think the code is wrong or it remains after your details should be available, contact HMRC or ask your payroll team what information they need.

Does M1 mean Marriage Allowance?

No. In 1257L M1, M1 is the “month 1” emergency-tax suffix. It is different from a code ending in M, such as 1383M, which can indicate that you receive Marriage Allowance.

Check your own payslip

Use the tools below to interpret the exact code on your payslip and compare the estimated deductions with what you were actually paid.

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Official sources

HMRC explains that M1, W1, X and NONCUM are emergency/non-cumulative markers, and that emergency codes are often used while a new employer waits for previous pay details. Read HMRC's emergency tax-code guidance and its explanation of tax-code letters and numbers.

Reviewed: 28 July 2026. This guide is general information, not personal tax advice.