Emergency Tax Code Explained — Why It Happens and How to Get It Fixed

Updated for 2026/27 rates. Information only — not tax or legal advice.

What Is an Emergency Tax Code?

An emergency tax code is a temporary code HMRC or your employer applies when they don't yet have your full tax history — typically shown as 1257 W1, 1257 M1, or 1257 X on your payslip.

Unlike your normal cumulative tax code (which spreads your £12,570 Personal Allowance evenly across the year and accounts for tax already paid), an emergency code calculates tax on a non-cumulative basis — each pay period is treated in isolation, as if it were the first of the year.

What Do W1, M1 and X Mean?

Suffix	Meaning
W1	Week 1 basis — used if you're paid weekly
M1	Month 1 basis — used if you're paid monthly
X	Generic marker meaning "non-cumulative," used when the exact basis isn't specified

Why Does This Happen?

No P45 provided: the most common cause — without your previous employer's P45, your new employer doesn't know your year-to-date pay and tax.
Started mid-year with incomplete starter checklist: if the starter checklist (which replaced the old P46) wasn't filled in correctly.
Complex circumstances: multiple jobs, benefits in kind, or a recent change HMRC hasn't processed yet.

Does This Mean I'm Overpaying Tax?

Often, yes — especially if you've already used some of your Personal Allowance earlier in the tax year at a previous job. Because an emergency code doesn't account for that, you can end up paying more tax than you actually owe for that pay period.

The good news: this usually self-corrects. Once HMRC receives your P45 or processes your starter checklist, they issue your proper cumulative tax code, and any overpayment is refunded automatically through payroll — no separate claim needed in most cases.

What Should I Do?

Give your new employer your P45 as soon as possible, or complete the starter checklist accurately if you don't have one.
Check your payslip in the following month or two — the code should update automatically to a standard cumulative code (usually 1257L).
If it hasn't corrected after 2-3 pay periods, contact HMRC directly via your Personal Tax Account.

Related Calculators

Take-Home Pay Calculator

Full salary breakdown

PAYE Calculator

Income Tax & NI breakdown

Required Salary Calculator

Gross needed for a target take-home

Pension Contribution Calculator

Auto-enrolment & salary sacrifice

Check Your Own Numbers

Rules like these are easier to apply once you can see your actual take-home pay, tax and NI broken down.

Open the Take-Home Pay Calculator →

Written using published HMRC guidance and gov.uk rules, current as of 2026/27. Not a substitute for personalised advice — for your specific circumstances, consult gov.uk or a qualified adviser via the FCA Register.

Frequently Asked Questions

Will I get back the extra tax I paid on an emergency code?

In most cases yes, automatically — once your correct cumulative tax code is applied, any overpayment from earlier in the year is refunded through your payslip, without you needing to claim separately.

Is an emergency tax code the same as a BR code?

No — BR taxes all income at 20% with zero Personal Allowance, while an emergency code (1257 W1/M1/X) still gives you the standard Personal Allowance, just calculated per pay period rather than cumulatively across the year.

How long does an emergency tax code usually last?

Typically one to three pay periods while HMRC processes your P45 or starter checklist — though it can take longer if your situation is more complex (multiple jobs, recent self-employment, etc.).

Can I avoid being put on an emergency tax code?

Providing your P45 to a new employer promptly, or filling in the starter checklist accurately if you don't have one, is the best way to avoid or minimise time on an emergency code.