Tax Code 1257L M1 Explained

1257L M1 (monthly) or 1257L W1 (weekly) means you get the standard £12,570 Personal Allowance, but it is applied on a non-cumulative basis: each payday is taxed as if it were the only pay in the year. Payroll ignores what you earned and paid earlier in the tax year. It is often called an emergency tax code and is usually temporary.

Tax-free allowance implied by this code: £12,570 a year (£1,047.50 a month).

How your pay is taxed on 1257L M1

Each month you get exactly 1/12 of the allowance (£1,047.50) and 1/12 of each tax band – no catch-up. On a steady £2,500 a month (£30,000) in England, tax is the same as 1257L: about £290.50 a month. The difference shows when your pay is uneven or you start mid-year. Example: you were unemployed from April to September and start a £2,500/month job in October. On cumulative 1257L, payroll would give you six months of unused allowance in October and you'd pay no tax that month. On 1257L M1 you pay £290.50 in October and every month after, so you overpay around £1,743 for the year (6 × £290.50) – which HMRC refunds once your code is corrected or after the year ends.

Tax-free allowance from this code£12,570Cumulative

Income tax with this code	£3,486
Income tax with standard 1257L	£3,486
Difference per month	£0.00

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Why you might have this code

You started a new job and ticked Statement B on the starter checklist (this is now your only job but you had another since 6 April).
Your new employer did not have your P45 details for this tax year.
HMRC issued a code change late in the year and told payroll to apply it non-cumulatively.
You started receiving a new pension or a taxable benefit part way through the year.

What to do

Check the code HMRC holds for you in your personal tax account (GOV.UK sign-in) or the HMRC app – it also shows how the number was worked out.
Compare it with the code on your latest payslip. If they differ, ask payroll whether they have applied HMRC’s latest notice.
Give payroll your P45 if you have one – this usually moves you onto a cumulative code.
If you are still on M1/W1 after about 35 days, update your employment details in your personal tax account or the HMRC app, or contact HMRC.
Any overpayment is normally refunded through payroll once the cumulative code arrives, or by P800 after 5 April.

See all tax codes or check your take-home with the UK salary calculator.

The monthly maths on 1257L M1

On 1257L M1, payroll uses only the figures for a single month: one-twelfth of the £12,570 allowance (£1,047.50), one-twelfth of the £37,700 basic-rate band (£3,141.67) at 20%, and 40% on anything above that. Weekly-paid staff on 1257L W1 get one fifty-second of each: £241.73 tax-free and £725.00 of basic-rate band a week.

HMRC describes the purpose of the week 1 / month 1 basis in its PAYE Manual: it stops an employer either making heavy deductions or paying a refund. That makes it a deliberately cautious setting. It is mainly used when HMRC or the employer doesn’t yet know the full picture.

Worked example: a bonus month

Non-cumulative codes don’t only overtax people who start mid-year. They also overtax lumpy pay. Say you earn £2,500 a month in England and receive a £3,500 bonus in month 6, making that month £6,000.

On 1257L M1, the bonus month is taxed as if you earned £72,000 a year. After the £1,047.50 of free pay, the first £3,141.67 is taxed at 20% and the rest at 40%, giving £1,352.67 of tax that month instead of the usual £290.50.

On cumulative 1257L, payroll compares your pay to date with six months’ worth of allowance and band. Your year-to-date taxable pay is still well inside the basic-rate band, so the whole bonus month is taxed at 20%: £990.50. The extra £362.17 taken on M1 isn’t refunded by payroll. It comes back only through a corrected code or a P800 after 5 April.

Pension withdrawals taxed on an emergency basis

The same monthly maths explains large tax bills on one-off pension withdrawals. If a provider applies 1257L M1 to a single £30,000 taxable payment, it treats that month as if you’d receive £360,000 a year. That gives £11,878.88 of tax. If £30,000 is your only income for the year, the tax actually due is £3,486.

HMRC has separate refund forms for this. Use P55 if you’ve flexibly accessed only part of your pension. Use P53Z if you’ve flexibly accessed all of it. Use P50Z if you’ve flexibly accessed all of it and have stopped working. Otherwise, the overpayment is corrected after the tax year ends.

When HMRC chooses M1 on purpose

Not every M1 code is an emergency code from a new job. When HMRC reduces your code part-way through the year – for example after you report a new company car – it works out the extra tax due for the whole year. It then issues the new code on a week 1 / month 1 basis so that the extra tax is collected evenly over the months that are left. HMRC calls this an in-year adjustment.

HMRC’s manual lists a few exceptions. If the extra tax up to the date of the change is under £15, the code stays cumulative. Late in the year (from 6 January), if the extra tax is £15 or more but less than £100 is due between the change and 5 April, the code may be issued as “not operated” so the employer doesn’t apply it. Most other code reductions are issued on a month 1 basis.

How long it takes to switch back

After you update your details online, HMRC tells you and your employer the new code within 15 working days.
If you’re paid monthly, the new code should appear on your next payslip or the one after. If you’re paid weekly, expect it on your third payslip.
If you’ve just started a job, GOV.UK asks you to wait 35 days before contacting HMRC, because it may still be waiting for your employer’s first payroll report.
If your M1 code was issued for a new benefit or the State Pension, it usually stays until 5 April. Your employer then drops the M1 in the new tax year.

Frequently asked questions

Do I pay more tax on 1257L M1?

Not if your pay is the same every month and you've worked all year. You overpay if you had months with little or no income earlier in the year, because that unused allowance isn't given back.

How long does 1257L M1 last?

GOV.UK says it usually takes up to 35 days for an emergency code to be replaced once HMRC has the right details. Codes issued for new benefits or pensions can last until the end of the tax year.

Is 1257L X the same as M1?

Yes in effect. X is used when pay dates are irregular; like M1 and W1, it means non-cumulative.

Will I get a refund?

If you overpaid, payroll usually refunds it when your code switches to cumulative 1257L. Otherwise HMRC reconciles your tax after 5 April and sends a P800 calculation.

Why was I given 1257L M1 after reporting a company car?

HMRC worked out the extra tax due for the whole year and set your code on a month 1 basis so that it’s collected evenly over the remaining months. That is deliberate, not an emergency code.

Does M1 carry over into the next tax year?

No. HMRC’s employer guidance tells payroll not to carry the W1 or M1 part of a code into the new tax year. The code becomes cumulative from 6 April.

I was emergency-taxed on a pension withdrawal. Which form do I use?

P55 if you’ve taken only part of your pension, P53Z if you’ve taken the whole pot, or P50Z if you’ve taken the whole pot and stopped working. HMRC also has an online tool that tells you which route to use.

Sources

Figures are taken from official government publications and were last reviewed on 2026-10-03.