Emergency Tax Refund: How to Get Back What W1, M1 and 0T Took

Emergency tax is the single most common reason people go looking for a refund, and it is also the most misunderstood, because the amount it costs depends almost entirely on something nobody thinks about: what month you started.

Here is what the code actually does, what it costs at different starting points, and the two different processes for getting the money back depending on whether the year has ended.

All figures are estimates on published 2026/27 rest of UK rates. Confirm your own position with HMRC.

How to tell if you are on one

HMRC's emergency tax code guidance is precise. You are on an emergency code if your code ends in:

• W1, used when you are paid weekly, for example 1257L W1
• M1, used when you are paid monthly, for example S875L M1
• X, used when your pay dates vary, for example C663L X

It adds that "you could also see 'NONCUM' on your payslip, depending on your employer's payroll software", and that "if your tax code does not end in W1, M1, X or NONCUM, you're not on an emergency tax code".

That last line rules out two codes people constantly describe as emergency tax. BR taxes everything at 20% with no allowance. 0T removes your allowance and applies the normal bands. Neither is an emergency code in HMRC's sense, both are perfectly correct on a second job, and both are expensive on your only one. The refund route is the same, so this guide covers them too. Our W1 and M1 pages cover the mechanics of each.

Why the month you started decides the damage

Normally your tax is worked out cumulatively: HMRC spreads your £12,570 Personal Allowance across the year and each payday looks at your total income and total allowance so far. An emergency code throws that away. In HMRC's words, "your tax is worked out based on what you're paid in that week or month only" and "you get taxed as if you're paid that amount every week or month of the year".

If you have been earning steadily since April, the two approaches give nearly the same answer. If you have months of unused allowance sitting behind you, they do not.

Example: £32,000 salary, £2,666.67 a month.

The October starter loses roughly £324 every month until the code is corrected, and none of it comes back through payroll until the code changes or the year is reconciled. Six months on an emergency code from an October start is close to £1,900.

This is why "am I on emergency tax" is only half the question. The other half is "since when".

Why it happened

HMRC's own explanation for new starters: "If your new employer does not have your previous income and tax details, you'll be paid using an emergency tax code. This is usually temporary."

The fix HMRC points to first is the P45: "If you've got a P45 from your previous job, give it to your new employer. This gives them your details and can help take you off the emergency tax code. If your previous employer did not give you a P45, ask them for one." Without one, your employer should use the starter checklist instead.

Then the timescale that matters: "HMRC will usually update your tax code when they get all your details from your new and previous employers. They'll send the tax code to you and your new employer. This can take up to 35 days from when you start your job."

There is a second, quite different case. HMRC notes you might be put on an emergency code if you "start getting company benefits or the State Pension", and that this "is normal and helps you pay the right amount of tax for that tax year". In that case, "You'll have an emergency tax code until the end of the tax year. In the new tax year, you'll be put on a non-emergency tax code." That one is working as intended and does not need fixing, though it is still worth checking the benefit or pension figure in your code is right.

Getting the money back: the current year

While the tax year is running there is no claim to make. Correct the code and payroll returns the overpayment.

1. Give your employer the P45, or complete a starter checklist if you do not have one.
2. Wait out the 35 days if you have just started. HMRC is explicit that this is the normal window.
3. If it is past that, check your code in your Personal Tax Account, confirm the jobs and pensions listed are right, and update anything that is not.
4. Watch your next payslip. When a cumulative code replaces the emergency one, the catch-up appears as a much lower deduction or a refund line in that pay run.

HMRC's own note is short and useful: "If you've paid too much tax, you can get a tax refund." And if you started more than 35 days ago and the code is still wrong, its advice is to find out how to update it rather than continue waiting.

Our guide to what to do about a wrong tax code has the steps, and how to change your tax code covers contacting HMRC.

Getting the money back: an earlier year

This is the part people miss. An emergency code that was never corrected before 5 April does not sort itself out with the new tax year. The new year starts clean, and the overpayment from the old one stays where it is until either HMRC reconciles it or you claim it.

HMRC may send a P800 for that year, since a mid-year job change is on its own list of triggers. But a P800 is only generated where the records flag a discrepancy, and letters go out any time between June and March of the following tax year, so waiting is not a plan.

For a completed year, use Check your Income Tax for previous years, compare HMRC's calculation against your P60, and contact HMRC with the specific figures if they disagree. You can go back four tax years, which means 2022/23 is still open until 5 April 2027 under the limit set out in HMRC's Self Assessment Claims Manual at TMA 1970 s43.

If you have changed jobs more than once in the last four years, check each of those years rather than only the most recent one. Emergency codes cluster around job changes, and one uncorrected year is as claimable as another.

Our full reclaim guide walks the whole multi-year recovery, and how to claim a tax refund from HMRC picks the right route for each year.

Check every year at once

The fastest way to see whether an emergency code cost you anything, and how much, is to check the code you were on against the code you should have been on, for each year still open.

Our free tax code checker does that for any year back to 2022/23, and the P800 refund checker frames the same calculation around a refund total. Both produce estimates to take to HMRC, not claims in themselves.