Emergency tax codes (W1, M1, X): why and how to fix

Starting a new job and finding more tax on your first payslip than you expected is a common shock. Often the reason is an emergency tax code. This guide explains what the code means, why it’s used, how much it can cost you in the short term, and how to get your money back.

How to tell if you’re on an emergency code

Your tax code is on your payslip. You’re on an emergency basis if it ends in:

• W1 (week 1), used if you’re paid weekly, for example 1257L W1;
• M1 (month 1), used if you’re paid monthly, for example 1257L M1;
• X, used by some payroll systems for the same thing.

Some payslips show NONCUM (non-cumulative) instead. GOV.UK’s page on emergency tax codes lists all of these. If your code doesn’t end in one of them, you’re not on an emergency code, although your code may still be wrong for other reasons. Our guide to tax codes explains how to read the rest of it.

Cumulative and non-cumulative tax

Normally PAYE is cumulative. Each payday, your employer looks at your total pay since 6 April and your tax-free allowance so far, and takes the tax due on the total, minus the tax already paid. If you start a job part way through the year after a gap, you get the benefit of all the allowance you haven’t used.

On an emergency code, each payday is treated on its own. You get one month’s share of your allowance, about £1,047.50 a month with the standard code, and the bands are applied to that month’s pay alone. You’re taxed as if you earned the same amount every month of the year. Earlier pay and earlier tax are ignored.

Why you were put on one

The most common reasons are:

• You started a new job without a P45, so your employer didn’t know your pay and tax so far this year.
• You started a second job or a pension alongside a job.
• You started getting a company benefit, such as a company car, or the State Pension, and HMRC needs to adjust your code.
• HMRC has issued an in-year code change and wants it applied without looking back over earlier pay.

When you start a job, your employer tells HMRC on your first payday. HMRC then matches up the details from your old and new employers and sends a proper code. This can take up to 35 days.

How an emergency code affects your pay

Whether you pay too much or too little depends on what happened earlier in the tax year.

If you had a gap before the new job, you usually overpay. Say you start a job paying £36,000 a year in October, the seventh month of the tax year, and you’ve had no other income since April. On a cumulative code, your first payslip would include seven months of allowance, about £7,332.50, which is more than that month’s pay. The tax would be £0.00. On 1257L M1, you’d pay roughly £390.50 a month instead, until the code is fixed.

If you moved straight from another job, an emergency code is usually close to right, because you’ve already used your allowance for the months so far. You may underpay slightly if your old job paid more.

If your code is 0T on an emergency basis, you get no allowance at all. On £36,000 a year, that’s about £600.00 of tax a month, compared with about £390.50 on the standard code.

How to get off an emergency code

1. Give your new employer your P45 from your last job. If you don’t have one, ask your old employer for it. If you can’t get one, fill in your new employer’s starter checklist, which asks about other jobs and benefits.
2. Check your details with HMRC using the Check your Income Tax service or the HMRC app. Make sure your old job has an end date and your new job is listed.
3. Wait for the new code. HMRC sends it to you and your employer. If you’re paid monthly, it should appear on your next or following payslip.
4. If nothing has changed after 35 days, contact HMRC or update your details online.

Getting overpaid tax back

When your employer starts using a normal cumulative code, the payroll software works out the tax due on your total pay so far and compares it with what you’ve paid. Any overpayment is usually refunded straight away in your next pay. You don’t need to make a separate claim.

If the code isn’t fixed before the end of the tax year, HMRC checks your records after 5 April. If you’ve paid too much, it sends a tax calculation letter (a P800) that tells you how to claim the refund. Our guide to claiming a tax refund explains the process step by step.

If you’ve underpaid, HMRC normally collects the difference by adjusting your tax code for a later year, so you don’t pay it all at once.

Emergency codes on pensions

Emergency codes are common when you start taking money from a pension, especially if you take a lump sum that isn’t fully tax-free. The provider may tax the first payment as if you’ll receive the same amount every month, which can mean a large overpayment. You can claim it back from HMRC during the year using the forms on GOV.UK, rather than waiting until the year ends.

Checking your first payslips

When you start a job, compare your first few payslips with an estimate of what you should take home. Our take-home pay calculator shows the figure on a normal code, and you can enter your emergency code there to see the difference. If you have more than one job, the two jobs tax calculator shows how the codes on each job affect your pay. Our guides to reading your payslip and P45s and P60s explain the paperwork you’ll see along the way.