An emergency tax code is a temporary code your employer uses when HMRC has not yet told them your correct one, most often when you start a new job without a P45. It usually gives you the standard tax-free allowance but treats each pay period on its own, which can take too much tax until the code is corrected. The fix is to give your employer the right information and check your details with HMRC; any overpaid tax is normally refunded.
Note: this is general information, not tax advice. The examples are estimates based on the 2026/27 rates and a simple employment. Your own situation can differ, so check your code and any refund on GOV.UK or with HMRC.
What an emergency tax code looks like
On a payslip, an emergency code is usually the standard code with a marker that says tax is not being worked out on a running total. The marker is W1, M1 or X, so you may see 1257L W1 (weekly pay), 1257L M1 (monthly pay) or 1257L X. The number part, 1257, is the usual £12,570 Personal Allowance, so the code is not a penalty rate and it is not a sign you owe money. The difference lies in how the tax is worked out, as the next section explains. Tax codes explained: what 1257L means describes the normal letters and numbers in detail.
You might also hear “emergency code” used loosely for other codes that look alarming, such as BR, which taxes all your pay at 20% with no allowance, or 0T, which gives no allowance at all. Those are normally not emergency codes in the formal sense, but they can behave similarly and are fixed in the same way. If you are unsure, ask your payroll department what your code means for your situation.
Why you end up on one
HMRC and your employer share information through the PAYE system. Your employer needs a tax code before the first payday, and if it does not have the details it needs, it applies an emergency code rather than guess. The usual triggers are:
- You started a new job and have no P45. A P45 comes from your previous employer when you leave and shows your pay and tax so far this tax year.
- Your employer was slow to receive a code from HMRC. Codes are sent electronically, and a delay in the first payroll can lead to the emergency code being used.
- You have just left university or been out of work. There is no previous employment record for HMRC to build on.
- You moved from self-employment, or came from abroad. HMRC has no recent employee record.
- You started a second job and your details are incomplete. In that case, you may see BR rather than the emergency code, because the allowance is already being used elsewhere.
When you start a job without a P45, your employer should ask you to complete a starter checklist. It asks whether this is your first job since 6 April, whether you have another job or a pension, and whether you have a student loan. Your answers decide which code your employer uses until HMRC says otherwise. If you ticked the wrong box, the code can be wrong from day one.
How the emergency basis can take too much tax
Normal PAYE works on a cumulative basis. Each month your employer adds up your pay and your tax-free allowance for the year to date. If you have had less pay than allowance so far, no tax is due, and unused allowance carries forward. An emergency code works on a week 1 or month 1 basis. Each payday is treated as the first of the year, so you get only one period’s allowance and nothing carries forward.
If you have been working all year at a steady wage, the two methods give the same answer, which is why people who join in April are rarely hurt. The difference shows when you start part-way through the year with nothing earned before. Take someone who starts in October 2026 on £30,000 a year, paid £2,500 a month, with no earlier pay that tax year. Their monthly allowance is £12,570 ÷ 12 = £1,047.50.
On the emergency month 1 basis, tax is £2,500 − £1,047.50 = £1,452.50, and 20% of that is £290.50 each month. Over October to March, six payments, that is £1,743.00.
On the correct cumulative basis, the person is entitled to seven months of allowance by October (month 7), but has only had one month of pay:
| Month | Cumulative pay | Cumulative allowance | Tax due this month (cumulative) | Tax taken on emergency basis |
|---|---|---|---|---|
| Oct | £2,500 | £7,332.50 | £0.00 | £290.50 |
| Nov | £5,000 | £8,380.00 | £0.00 | £290.50 |
| Dec | £7,500 | £9,427.50 | £0.00 | £290.50 |
| Jan | £10,000 | £10,475.00 | £0.00 | £290.50 |
| Feb | £12,500 | £11,522.50 | £195.50 | £290.50 |
| Mar | £15,000 | £12,570.00 | £290.50 | £290.50 |
| Total | £486.00 | £1,743.00 |
The correct year-end tax is 20% of (£15,000 − £12,570), which is £486. The emergency basis took £1,743, so the overpayment is £1,257. That is 20% of the £6,285 of allowance that was never used because it was spread across six months only. HMRC works out the position again and refunds the difference once the right code is in place, either through payroll or after the end of the tax year, but it can mean months of lower take-home pay in the meantime.
For this salary, a standard code on a full year would give take-home pay of about £2,093 a month (£25,120 a year) from the House of Calculator engine. Over the first four months, the emergency basis takes £290.50 a month in tax where the cumulative basis takes nothing, so take-home pay on those payslips is that much lower. National Insurance is a separate calculation and does not change with the tax code.
What happens with National Insurance and student loans
An emergency tax code only affects income tax. Employee National Insurance is worked out on your earnings for each pay period and is not changed by the code. If you have a student loan, the repayments are based on your pay above the plan threshold and are also separate. But your starter checklist answer on student loans matters, because the employer takes repayments only if told to, and HMRC may later send a notice.
That means a payslip with an unexpectedly low take-home pay may have three causes: tax on the emergency basis, a student loan, or a pension contribution. Check each line against what you expect. How to work out your take-home pay from a UK salary walks through how each deduction is calculated.
How to get the code corrected
The aim is to get your employer an accurate code from HMRC. A practical order of steps:
- Look at your payslip. Check the code, and whether it has W1, M1 or X after it. Note your National Insurance number and your employer’s PAYE reference if shown.
- Give your employer your P45 or complete the starter checklist properly. If you now have a P45 from a previous job this year, hand it over. A P45 lets payroll use the cumulative basis.
- Check your personal tax account on GOV.UK. You can see your tax code, your employment history and whether any details are missing. You can also tell HMRC about a new job, other income or a benefit.
- Contact HMRC if the code does not change. The usual route is the online account or the helpline. HMRC will contact your employer and send a corrected code. Employers usually apply it from the next pay run.
- Keep your payslips. They show the tax paid and help to check the refund.
There is no need to wait until the end of the tax year to chase this. If your employer receives a new code part-way through the year, it usually adjusts your tax in the next payroll and refunds the excess through your wages. HMRC does not charge you for fixing the code.
Getting the refund
If the emergency code took too much tax, the refund can arrive in one of three ways:
- Through payroll. When the new code arrives, your employer recalculates your tax on a cumulative basis from the start of your employment, and the overpaid amount shows as a lower tax figure or a one-off adjustment on a later payslip.
- After the tax year ends. HMRC may review your record and send a P800 tax calculation if you have overpaid. It will say how much and how you will be repaid.
- Through your personal tax account. You may be able to claim a refund online. Beware of websites that charge a fee to claim a refund for you, because you can do this yourself for free through GOV.UK.
If you left the job before the code was corrected, you may need to claim the refund yourself using a form or your online account. Ask HMRC what applies, because it depends on whether you have started another job since.
Common mistakes that keep people on the emergency code
- Ignoring the starter checklist or leaving it blank, so payroll has nothing to use.
- Ticking that this is your only job when you have another one, which later leads to underpaid tax and a code change in the other direction.
- Assuming the code is a punishment and leaving it, which can cost hundreds of pounds.
- Throwing away your P45 or forgetting to hand it to your new employer. Keep the copy you are given and pass on the parts meant for the new employer.
- Waiting for the end of the year to fix it, rather than asking HMRC now.
- Assuming a tax code alone explains a low payslip, when pension, student loan or unpaid leave might also be the cause.
If your pay seems low, use the take-home calculator below to work out what a standard code would give you at your salary. If the difference between that figure and your payslip is large, and is not explained by a pension or loan, the code is the next thing to check.
Try the calculator
Enter your salary, region, student loan plan and pension in the UK Take-Home Pay Calculator to see what your pay would be on a standard code, then compare it with your payslip. The gap can help you see whether the tax code is the cause.
Frequently asked questions
What is an emergency tax code?
It is a temporary code used when your employer does not have your correct one. It typically gives the standard allowance on a week 1 or month 1 basis, shown as W1, M1 or X after the code, and is replaced once HMRC supplies the right code.
How long does an emergency tax code last?
It usually lasts until HMRC sends your employer a correct code, which can take a few weeks. You can speed it up by giving your employer your P45 or completing the starter checklist, and by checking your details in your personal tax account.
Will I get my money back if I was on an emergency tax code?
Usually yes, if you paid too much. The refund comes through your payroll when the code is corrected, or from HMRC after the end of the tax year. Check GOV.UK for the process and avoid companies that charge a fee to do it for you.
Does an emergency tax code affect National Insurance?
No. National Insurance is calculated separately on your earnings and does not depend on your tax code. Student loan repayments are also separate.
Can an emergency tax code mean I owe tax?
It can in some cases, for example if you have other income or a second job that HMRC does not know about. Normally it is the other way round, with the code taking too much, but you should check your records with HMRC.