What does the tax code
1257L M1 mean?
1257L M1 is the emergency form of the UK standard code. Same £12,570 allowance, different mechanics: each payslip is taxed on its own, which is why mid-year starters overpay.
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Get the detailed breakdown + free reclaim guideThe confusing thing about 1257L M1 is that the allowance is not the problem. 1257L on its own is the correct standard code for 2026/27 and gives you the full £12,570. The two characters after it change how that allowance is handed to you, and for anyone who did not work a full tax year from 6 April, that difference is expensive.
- 1257L M1 Tax Code
- The standard 1257L code operated on a non-cumulative basis. M1 means monthly pay, W1 means weekly, and X is the generic marker used by some payroll systems. Each pay period is taxed as if it were the only one in the year, using one period's worth of Personal Allowance and ignoring everything earned or taxed before it.
M1, W1, X and W1/M1 are the same thing
Payslips render this code in at least five different ways and they all mean one thing: non-cumulative.
- 1257L M1 and 1257L Month 1 appear on monthly payrolls
- 1257L W1 and 1257L Week 1 appear on weekly payrolls
- 1257L W1/M1 is the version most payroll software prints regardless of your pay frequency
- 1257LX is the same instruction compressed into a single character
There is no practical difference between them. If you searched for one of these and found this page, the answer is the same whichever form your employer prints.
Cumulative versus non-cumulative, in one paragraph
A normal 1257L code is cumulative. Every payday, your employer recalculates your tax on everything you have earned since 6 April against everything you have paid so far, and charges the difference. Allowance you did not use in an earlier month is still available later. The system is self-correcting.
A 1257L M1 code throws all of that away. Your employer looks only at this period's pay, subtracts one period's allowance, taxes the remainder, and starts again from scratch next time. Unused allowance from earlier months is simply lost. Nothing self-corrects, because the code has no memory.
If you are paid an identical amount every month from April onwards, the two methods happen to produce the same answer. That is why some people sit on an M1 code for a whole year and never notice. Break the pattern in any way and they diverge sharply.
Worked example: what M1 costs a mid-year starter
Take someone who was out of work from April, then starts a job on 1 October paying £32,000 a year. They receive six monthly payslips before the tax year ends on 5 April. Their code is 1257L M1.
Monthly gross pay is £2,666.67 and one month of allowance is £1,047.50.
On 1257L M1, every month is identical: £2,666.67 minus £1,047.50 leaves £1,619.17 taxable, taxed at 20%, giving £323.83 of tax per month. Across six months that is £1,942.98.
On a cumulative 1257L, the calculation follows the year to date:
| Month paid | Pay to date | Allowance to date | Taxable to date | Tax that month |
|---|---|---|---|---|
| October | £2,666.67 | £7,332.50 | £0 | £0 |
| November | £5,333.34 | £8,380.00 | £0 | £0 |
| December | £8,000.01 | £9,427.50 | £0 | £0 |
| January | £10,666.68 | £10,475.00 | £191.68 | £38.34 |
| February | £13,333.35 | £11,522.50 | £1,810.85 | £323.83 |
| March | £16,000.02 | £12,570.00 | £3,430.02 | £323.83 |
Total cumulative tax: £686.00, which is exactly 20% of the £3,430 by which their £16,000 of earnings exceeds the full £12,570 allowance.
The M1 code took £1,942.98. The correct figure was £686.00. The overpayment is £1,256.98.
None of that comes back through payroll while the M1 code is still running. Figures are income tax only, exclude National Insurance, and are an estimate to confirm with HMRC.
Who ends up on 1257L M1
Starting a job without a P45. The most common route. Your new employer has no record of your pay and tax so far, so they operate the code non-cumulatively until HMRC supplies the year-to-date figures.
Starting after a gap. Time between jobs, a career break, coming back from travelling, or a first job starting part way through the year. This is the group the worked example above describes, and the group that loses the most.
A second job that becomes your main one. Payroll changes often land as a fresh employment record, which restarts the process.
Company benefits changing sharply. HMRC sometimes issues a non-cumulative code deliberately to stop a large mid-year correction hitting one payslip.
Starting a pension drawdown. Pension providers commonly apply an emergency code to the first payment, which is why one-off withdrawals are so often overtaxed.
Why pension withdrawals get hit hardest
The single most expensive place an emergency code turns up is not employment at all. It is the first payment out of a defined contribution pension.
Pension providers usually have no tax code for you when you take money for the first time, so they operate an emergency code on a month 1 basis. The system then treats that single withdrawal as if it were one month of a much larger annual income and taxes it accordingly. Someone taking a one-off £30,000 payment can find tax deducted as though they were going to receive £30,000 every month for a year, pushing part of it into the higher and additional rate bands that their real annual income never reaches.
The money is recoverable, and for pension withdrawals there are dedicated HMRC forms for reclaiming it rather than waiting for the year to reconcile. The general point is the same as everywhere else on this page: the emergency code is not a judgement about you, it is what happens when a payer has to calculate tax without information.
How to read your payslip and be sure
Payslips are inconsistent, so it is worth knowing exactly where to look.
The tax code is usually printed near your National Insurance number in the header block, not in the deductions table. Read the whole field, including anything after the letters. "1257L" and "1257L M1" occupy almost the same space and are easy to conflate at a glance.
The second tell is the year-to-date columns. A cumulative code makes sense of them: taxable pay to date times the right rate should broadly reconcile to tax to date. Under a non-cumulative code it will not reconcile, because the year-to-date tax figure is just the sum of independent monthly calculations. If the two numbers refuse to agree with each other, that is your answer even if the code itself is printed ambiguously.
How to get it removed
Give your employer your P45. If you have one from a previous job in the same tax year, hand over parts 2 and 3. This is the fastest fix and often the only one needed.
Complete a Starter Checklist. No P45 means your employer needs this instead. Answering it accurately is what lets HMRC issue a cumulative code rather than leaving you on the emergency basis.
Check your Personal Tax Account. Sign in at gov.uk/personal-tax-account, confirm the employment is showing correctly and that no old job is still listed as live. A ghost employment is a common reason a cumulative code never arrives.
Call HMRC. The Income Tax helpline is 0300 200 3300. Ask specifically for a cumulative code to be issued to your employer. Have your National Insurance number and payroll reference ready.
Once a cumulative code reaches your employer, the correction happens automatically on the next payday. Your employer recalculates the year from 6 April, finds the overpayment, and refunds it in that payslip. In the worked example above, that single payslip would be around £1,257 larger than usual.
If the tax year has already ended
This is where people lose money. A cumulative code fixes the year it is issued in. It does nothing for a year that has already closed.
If you were on 1257L M1 during 2025/26 or earlier and never received a corrected code, the overpayment is still sitting with HMRC. It may come back on its own through a P800 calculation, but only if HMRC's records flag the discrepancy, and they do not always do so. Our guide to reclaiming overpaid tax covers the four-year claim window, which currently reaches back to 2022/23 and closes for that year on 5 April 2027.
You can estimate what an emergency code cost you, year by year, with our free tax code checker. Treat the result as an estimate to take to HMRC rather than a final figure.
People also ask
- 1257L M1 gives the full £12,570 allowance but spreads it one period at a time with no memory of earlier months
- M1, W1, W1/M1, Month 1, Week 1 and 1257LX all mean exactly the same thing: non-cumulative
- On steady pay from April it costs nothing, which is why it goes unnoticed for months
- Starting work part way through the year is where it hurts: about £1,257 overpaid in the worked example
- A P45 or a completed Starter Checklist is usually all it takes to get a cumulative code issued
- Once a cumulative code arrives, the refund lands automatically in your next payslip
- For a tax year that has already closed there is no automatic refund, and the claim window is four years
Related tax codes: 1257L tax code | M1 tax code | W1 tax code | 0T tax code | Wrong tax code?
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