Emergency tax codes: 1257L W1/M1 refunds
Last updated: 12 October 2026
What an emergency code looks like on a 2026/27 payslip, why a new job uses one, and what GOV.UK says about putting it right.
How to spot an emergency code
GOV.UK says you are on an emergency tax code when the code ends in W1, M1 or X. W1 is the weekly version, M1 is the monthly version, and X is used when your pay dates vary. A payslip may also say NONCUM, which means the same non-cumulative treatment. The code in front of those letters is often 1257L, so the payslip reads 1257L W1 or 1257L M1. Scottish codes start with S and Welsh codes start with C, and they can carry the same ending, for example the S875L M1 illustration on the GOV.UK page.
If the code does not end in W1, M1, X or NONCUM, it is not an emergency code. A plain 1257L is the ordinary cumulative code for someone whose personal allowance is the standard £12,570. The letters at the end are the part that changes the calculation. Check the code on the payslip, not only the one in an old letter.
What 1257L is counting
The number in a tax code is the tax-free amount with the last digit dropped. 1257 is £12,570, the 2026/27 personal allowance published on GOV.UK for the tax year that runs from 6 April 2026 to 5 April 2027. L means you are entitled to that standard allowance. The allowance is smaller once adjusted net income goes above £100,000, and a code can also be reduced for benefits or an underpayment. Those adjustments produce a different number. 1257L itself is the full standard allowance.
On a cumulative code, payroll looks at pay and tax from the start of the tax year. Each payday you receive one period’s share of the allowance, and any unused share from earlier weeks or months is still available. That is why a quiet month, or a job that starts late, often has a lower tax bill than a single month looked at on its own.
What W1, M1 and X change
An emergency code taxes the payment in front of it as if that payment were your pay every week or month of the year. It does not look back at earlier paydays in this employment, and it does not pick up unused allowance from months before you started. GOV.UK’s description is that tax is worked out on that week or month only. The result can be too much tax or too little. It is a way of paying something sensible before HMRC has the year’s figures, and it is a poor picture of the year as a whole.
The arithmetic for one isolated month is simple, and it is worth doing so the payslip has a check. The monthly share of £12,570 is £1,047.50. On a £3,000 payment taxed on a month-1 basis, the slice above that share is £1,952.50. At the basic rate of 20% the tax is £390.50. National Insurance is worked out on its own thresholds and is not switched off by an emergency code. A student loan deduction, if you have one, is also separate: it uses the plan threshold, not the tax code.
Why the same pay can be untaxed on a cumulative code
The gap shows up when the job starts late and the employer has no earlier pay and tax. Take someone whose first payday in this job is a £3,000 salary in January, with nothing else recorded for 2026/27. January is month 10 of a tax year that started on 6 April. On 1257L M1 the month is taxed on its own and the income tax is the £390.50 above.
On a cumulative 1257L, with no previous pay and no previous tax, ten months of allowance are available: £12,570 × 10 / 12 is £10,475. Pay of £3,000 sits inside that allowance, so the income tax on that payday is zero. The £390.50 was not a different rate. It was the emergency code ignoring the allowance from April to December. If the person is then paid £3,000 again in February and March, a cumulative code still has unused allowance to set against those months. The emergency code would charge £390.50 again each time, because each month is treated as typical of the whole year.
This illustration uses the published allowance and the basic rate. It is not an HMRC worked example, and it ignores Scottish rates, benefits, and any other job. If pay varies, or another job has already used the allowance, the cumulative bill moves. The income tax calculator shows the full-year bill once you know the year’s income. It cannot reconstruct a week-1 payslip.
A new job, a P45 and the starter checklist
GOV.UK says a new employer tells HMRC when you start. If that employer does not have your previous income and tax details, the first pay uses an emergency code, and that is usually temporary. Hand over the P45 from the previous job. It carries the code, the pay to date and the tax to date, which is what a cumulative calculation needs. If the old employer has not issued a P45, ask them for one. If there is no P45, the starter checklist is the form the GOV.UK emergency-code page points to. It tells the new payroll whether this is your first job of the year, a second job, or a job after another one.
HMRC usually updates the code within 35 days of you starting, and sends it to you and to the employer. If you started more than 35 days ago and the code still looks wrong, the same GOV.UK page sends you to the service for updating a tax code. The personal tax account at GOV.UK is the signed-in place to see the code HMRC holds and the pay employers have reported.
When the emergency code is meant to last the year
Two cases are different from a missing P45. GOV.UK says that starting company benefits, or starting the State Pension, can put you on an emergency code on purpose, so that the tax for the rest of the year is collected. You stay on it until the end of the tax year. The next tax year should begin on a non-emergency code. It is still worth checking that the code includes the benefit or the pension. If it does not, update the details in the tax-code service or contact HMRC, which is the instruction on that page.
There is a second reason a code can stick. If you have not paid enough tax, GOV.UK says you stay on the emergency code until the correct tax for the year has been paid. Leaving the code early would not, by itself, cancel an underpayment. The payslip is the record of what was deducted. Keep it.
Getting a refund if you paid too much
If the emergency code took too much, GOV.UK says you can get a refund. The practical route it points to is the tax-refund checker, which asks what the overpayment was on: pay from a job, a Self Assessment return, savings interest, and several other kinds of income. That checker does not itself pay the refund. It tells you which route applies. For a current job, the usual correction is a new cumulative code. The next payroll then looks at tax already deducted and pays the difference through wages, which can mean a month with little or no income tax.
This page does not give a phone number, a promised date for a P800, or a typical refund in pounds. Those details change, and unofficial write-ups often invent them. Use the emergency-code page, the personal tax account, and the refund checker. If you complete Self Assessment, the year’s employment income and tax deducted belong on the return, and any overpayment is part of that calculation rather than a separate payroll fix.
What to compare it with
A useful check is the year’s income on a normal code, set beside the emergency month. The take-home pay calculator uses cumulative 2026/27 rates for England, Wales, Northern Ireland or Scotland, including National Insurance. It assumes the personal allowance is spread in the ordinary way. It will not match a W1 or M1 payslip, and that mismatch is the point of the comparison. Add a student loan only in the student loan calculator, because the plan threshold is not part of the tax code.
Figures here follow GOV.UK’s emergency tax codes page and the 2026/27 personal allowance of £12,570. The January illustration is arithmetic on those figures, not a published HMRC example. Scottish income tax uses different bands, so a Scottish emergency code will not reproduce the £390.50. Nothing on this page is a tax code issued to you.