Why am I on an emergency tax code?

Almost always because your new employer does not have a P45 showing your pay and tax so far this year. Give them your P45 if you have one; otherwise HMRC sends a corrected code once it has details from your new and previous employers, which gov.uk says can take up to 35 days from when you start.

Does emergency code mean I'm paying more tax?

In most cases yes, temporarily. Non-cumulative calculation doesn't account for unused PA from earlier months, so you are usually over-taxed until the code goes cumulative. Any excess is refunded via subsequent payrolls or year-end reconciliation.

What is the emergency tax rate in the UK?

There is no separate emergency tax rate - the percentages are the standard 2026/27 Income Tax bands (20%, 40%, 45%). The reason emergency code costs more is that only 1/12th (M1) or 1/52nd (W1) of your £12,570 Personal Allowance is applied to each pay period, instead of the full year-to-date allowance. So the rate never goes above 20% for a basic-rate taxpayer: on £2,917 a month, M1 takes £374, about 12.8% of pay. The extra cost is that cumulative coding would often take less, or nothing, in the first months because allowance from earlier in the year is still unused.

How much extra tax does emergency code take?

It depends on when in the tax year you start, because the over-tax is the allowance from the months before you started: for a basic-rate taxpayer, 20% of 1/12 of the allowance for each earlier month. A £35,000 starter paid in June (tax month 3) overpays £419 in total. One paid first in October (tax month 7) has £6,285 of unused allowance, so M1 over-taxes the full £374 a month for 3 months and about £1,257 in all. It all comes back once the code goes cumulative, or after the tax year ends.

What's the difference between W1, M1 and X?

W1 is weekly (used if paid weekly), M1 is monthly, and X is a generic non-cumulative marker that can apply to any frequency. Functionally they operate identically - taxing each pay period in isolation against 1/52 or 1/12 of the Personal Allowance.

How do I claim back overpaid emergency tax?

For employment income, you almost never need to claim - HMRC moves you to a cumulative code once it has your year-to-date figures, and the next payroll refunds the over-paid tax. For a flexibly accessed pension payment, forms P55, P50Z and P53Z let you claim the over-tax back within the same tax year instead of waiting for year-end. If you've stopped working partway through the year and are not starting a new job, form P50 claims back tax you have overpaid.

Will I get a refund if emergency code over-taxed me?

Yes. Once HMRC converts you to a cumulative code (typically 1257L without the W1/M1/X suffix), the first cumulative payroll adjusts your year-to-date figures and refunds any over-paid tax through that payslip. If the tax year ends before that happens, HMRC's automatic year-end reconciliation issues a P800 calculation, sent between June and March of the following tax year, with refund instructions.

Is the old 50% emergency tax rule still in force?

No. There has not been a flat 50% emergency tax rate in modern PAYE - that figure is sometimes confused with BR (Basic Rate, 20% on everything) or with 0T (no allowance, taxed at marginal rates from the first pound), which is the week 1/month 1 code a new employer uses when you give it neither a P45 nor a Starter Checklist. The standard emergency code is 1257L W1/M1/X, which still gives you a slice of the PA each period.

Tax Code · 2026/27

Emergency Tax Code 2026/27: W1, M1 and X Suffixes

An 'emergency' tax code is a non-cumulative version of your main code. You'll see W1 (weekly), M1 (monthly), or X (either) appended - each pay period is taxed in isolation, which usually means you pay more tax than you owe.

Cite or embed - free under CC BY 4.0

What the 1257L W1/M1/X tax code means

Under normal PAYE, your employer calculates tax using year-to-date pay and allowance totals - this 'cumulative' approach smooths out any under- or over-collection across the year.

An emergency code (W1, M1 or X suffix) switches to non-cumulative - each pay period is taxed in isolation, as if it were the first week or month of the tax year. You get 1/52nd or 1/12th of your Personal Allowance applied each period, with no year-to-date adjustment.

The code itself is usually 1257L W1 (weekly) or 1257L M1 (monthly). The W1/M1/X signal that HMRC hasn't yet received your full year-to-date information from a previous employer or pension.

There is no separate 'emergency tax rate' - the bands and percentages are exactly the same as the standard 2026/27 Income Tax (20% basic up to £50,270, 40% higher to £125,140, 45% above). What changes is that unused Personal Allowance from earlier in the tax year cannot offset later pay, so the tax taken in any single period can be much higher than the cumulative figure you actually owe by 5 April.

When you'll see 1257L W1/M1/X

You've just started a new job and haven't provided a P45 from your previous employer.
You had no P45 and ticked Statement B on the Starter Checklist (this is now your only job, but since 6 April you have had another job or taxable Jobseeker's Allowance, Employment and Support Allowance or Incapacity Benefit) - the employer must use 1257L on a week 1/month 1 basis.
You had gaps in employment and HMRC is playing catch-up on year-to-date figures.
You moved from self-employment to employment mid-year.
You've taken a flexible payment from a pension - a new pension starts on a week 1/month 1 basis (HMRC PAYE Manual PAYE11120), and any over-payment can be reclaimed in-year with form P55, P50Z or P53Z.

What to do if you have a 1257L W1/M1/X code

Give your new employer your P45 at the earliest opportunity - it carries your year-to-date pay and tax, which is what a cumulative code needs. A Starter Checklist with Statement B keeps you on week 1/month 1 by design until HMRC sends a code.
Check your Personal Tax Account on gov.uk to see the code HMRC has on file and the reason for non-cumulative handling.
Once HMRC has the full year-to-date, they'll remove the suffix and issue a standard 1257L code. Any over- or under-tax from the emergency period is reconciled through the next payroll - you do not need to file self-assessment for this alone.
gov.uk says HMRC's updated code can take up to 35 days from when you start. If you started more than 35 days ago and are still on an emergency code, update your details with HMRC online or on 0300 200 3300.
For over-tax on a flexibly accessed pension payment, claim it back in the same tax year: P55 if you have not emptied the pot and will not take regular or flexible payments before the end of the tax year, P50Z if you have emptied it and stopped work, P53Z if you have emptied it and are still working.

Worked example

You start a new job on 1 June paying £35,000 a year (£2,917 a month) with no P45. You tick Statement B on the Starter Checklist (you had another job or taxable benefit since 6 April, but earned little from it), so your employer applies 1257L M1. In June, only 1/12 of the Personal Allowance (£1,047.50) is set against your £2,917, leaving £1,869 taxable at 20% - about £374 of Income Tax. On cumulative 1257L, a June payday falls in tax month 3, so three months of allowance (£3,142.50) sit against £2,917 of pay to date and the tax would be £0. In July, cumulative coding would take about £329 against £374 on M1. From August the two codes take the same £374 a month, because your pay to date has by then used up the allowance from April and May. So the over-tax is a one-off £419 - the two unused months of allowance (£2,095) × 20% - not a monthly loss, and it comes back in one go on the first cumulative payslip, or after the tax year ends if the code never goes cumulative.

Want to see the numbers for your own salary? Use the salary calculator and pick 2026/27 to see how 1257L W1/M1/X interacts with your full take-home.

Frequently asked questions about 1257L W1/M1/X

Why am I on an emergency tax code?: Almost always because your new employer does not have a P45 showing your pay and tax so far this year. Give them your P45 if you have one; otherwise HMRC sends a corrected code once it has details from your new and previous employers, which gov.uk says can take up to 35 days from when you start.
Does emergency code mean I'm paying more tax?: In most cases yes, temporarily. Non-cumulative calculation doesn't account for unused PA from earlier months, so you are usually over-taxed until the code goes cumulative. Any excess is refunded via subsequent payrolls or year-end reconciliation.
What is the emergency tax rate in the UK?: There is no separate emergency tax rate - the percentages are the standard 2026/27 Income Tax bands (20%, 40%, 45%). The reason emergency code costs more is that only 1/12th (M1) or 1/52nd (W1) of your £12,570 Personal Allowance is applied to each pay period, instead of the full year-to-date allowance. So the rate never goes above 20% for a basic-rate taxpayer: on £2,917 a month, M1 takes £374, about 12.8% of pay. The extra cost is that cumulative coding would often take less, or nothing, in the first months because allowance from earlier in the year is still unused.
How much extra tax does emergency code take?: It depends on when in the tax year you start, because the over-tax is the allowance from the months before you started: for a basic-rate taxpayer, 20% of 1/12 of the allowance for each earlier month. A £35,000 starter paid in June (tax month 3) overpays £419 in total. One paid first in October (tax month 7) has £6,285 of unused allowance, so M1 over-taxes the full £374 a month for 3 months and about £1,257 in all. It all comes back once the code goes cumulative, or after the tax year ends.
What's the difference between W1, M1 and X?: W1 is weekly (used if paid weekly), M1 is monthly, and X is a generic non-cumulative marker that can apply to any frequency. Functionally they operate identically - taxing each pay period in isolation against 1/52 or 1/12 of the Personal Allowance.
How do I claim back overpaid emergency tax?: For employment income, you almost never need to claim - HMRC moves you to a cumulative code once it has your year-to-date figures, and the next payroll refunds the over-paid tax. For a flexibly accessed pension payment, forms P55, P50Z and P53Z let you claim the over-tax back within the same tax year instead of waiting for year-end. If you've stopped working partway through the year and are not starting a new job, form P50 claims back tax you have overpaid.
Will I get a refund if emergency code over-taxed me?: Yes. Once HMRC converts you to a cumulative code (typically 1257L without the W1/M1/X suffix), the first cumulative payroll adjusts your year-to-date figures and refunds any over-paid tax through that payslip. If the tax year ends before that happens, HMRC's automatic year-end reconciliation issues a P800 calculation, sent between June and March of the following tax year, with refund instructions.
Is the old 50% emergency tax rule still in force?: No. There has not been a flat 50% emergency tax rate in modern PAYE - that figure is sometimes confused with BR (Basic Rate, 20% on everything) or with 0T (no allowance, taxed at marginal rates from the first pound), which is the week 1/month 1 code a new employer uses when you give it neither a P45 nor a Starter Checklist. The standard emergency code is 1257L W1/M1/X, which still gives you a slice of the PA each period.

All UK tax codes →

Sources & further reading

All figures and definitions on this page reflect the 2026/27 UK tax year and are cross-checked against HMRC guidance.

HMRC — What your tax code means (official meanings for L, BR, D0, D1, K, 0T, NT, M, N, S, C, T)
HMRC — Income Tax rates and Personal Allowance (2026/27 bands and thresholds)
HMRC — Emergency tax codes (W1, M1 and X suffixes)
HMRC — Rates and thresholds for employers 2026 to 2027
HMRC — Your Personal Tax Account (check your current code and how it was calculated)
Our methodology & calculation sources →