What is an emergency tax code?
An emergency tax code is a temporary code your employer uses when HMRC has not yet confirmed your correct code, usually 1257L with W1, M1 or X after it.
What an emergency tax code means
Your tax code tells your employer how much tax-free pay to give you through PAYE. When you start a new job without a P45, start a second job, or begin receiving a pension or company benefits, your employer may not know your full position. Until HMRC sends an updated code, the employer uses an emergency code.
For 2026/27 the emergency codes are 1257L W1 (weekly pay), 1257L M1 (monthly pay) and 1257L X. The suffix means the code is applied on a non-cumulative basis: each pay period is taxed on its own, ignoring what you have earned or paid earlier in the tax year.
Why you might pay too much or too little
On a normal cumulative code, if you started work part way through the year you would receive the tax-free allowance you had not used in earlier months. On a W1 or M1 code you only get one week's or one month's share of the allowance each payday. People who were not working earlier in the year therefore usually pay too much tax until the code is corrected.
The opposite can happen if you have a second job, a pension or taxable benefits: the emergency code gives a full allowance in a job where you should have little or none, and you may owe tax later.
Example
Sam started a new job in October on £36,000 a year (£3,000 a month), having not worked since April. With no P45, the employer used 1257L M1, giving £1,047.50 tax-free each month and taxing the remaining £1,952.50 at 20%: £390.50 a month.
On a cumulative 1257L code in October, Sam would have six months of unused allowance (£6,285) available, so little or no tax would be due that month. Once HMRC updated the code, the overpaid tax was refunded through Sam's next payslips.
Why it matters for you
Emergency codes are designed to be short term, but they can stay in place for months if nobody tells HMRC. Check your payslip after starting a new job. If it shows W1, M1 or X, complete the starter checklist with your employer, give them your P45 if you have one, and check your code in your HMRC personal tax account. Our guide to tax codes explains the letters in detail.
Common questions
Until HMRC sends your employer a corrected code, which usually happens within a few weeks of the employer reporting your details through payroll. If it is still on your payslip after two or three pay days, check your personal tax account or contact HMRC to speed it up.
Usually yes. Once your code is corrected to a cumulative code, overpaid tax is normally refunded automatically through your next payslips. If you leave the job or the tax year ends first, HMRC will refund it after the year end or you can claim through your personal tax account.
1257L on a non-cumulative basis, shown as 1257L W1 for weekly pay, 1257L M1 for monthly pay, or 1257L X. It is based on the standard personal allowance of £12,570, which is frozen at that level.