TL;DR: 1257L M1 is the standard UK PAYE tax code (1257L gives an annual tax-free personal allowance of 12,570 pounds) applied on a "month 1" non-cumulative basis. The M1 suffix tells the employer or pension provider to treat each pay month as a separate first month of the year, ignoring the year-to-date tax position. It is the most common "emergency" code that HMRC issues to new starters who join without a P45 from a previous employer in the same tax year. On weekly payrolls the equivalent is 1257L W1; the generic non-cumulative marker is 1257L X. The code typically over-deducts tax compared with a cumulative 1257L because it does not use any year-to-date unused allowance. HMRC normally fixes the position by issuing a cumulative code once it has the year-to-date information from RTI returns or from a P45 handed to the new employer, with any refund flowing through the next pay packet or via a P800 reconciliation after year-end.
Last reviewed May 2026
UK PAYE tax codes are made up of three components: a number (the tax-free annual amount divided by 10), a letter (the category code), and (where applicable) an operating-basis suffix. 1257L M1 brings together the standard personal-allowance code 1257L with the M1 suffix, meaning the code is operated on a monthly non-cumulative basis. Most employees on this code are new starters who joined without a P45.
This guide explains exactly what 1257L M1 does to a payslip, why HMRC issues it, what the relationship is with the cumulative version of the same code, how the monthly tax calculation works under the M1 basis, the routes back to a cumulative code, and how any overpayment is reclaimed.
The two halves of the code: 1257L and M1
1257L is the standard tax code for most UK working-age employees who are entitled to the full personal allowance. The 1257 represents the annual tax-free amount of 12,570 pounds (the personal allowance was set at this level for 2021-22 and has been frozen since). The L suffix indicates entitlement to the standard personal allowance for the tax year.
The M1 (month 1) suffix is the operating basis. Under a cumulative code, the employer recalculates the year-to-date tax position at each pay date - cumulative pay, cumulative tax due, and an adjustment to the current month's deduction to balance the year-to-date. Under an M1 code the employer ignores year-to-date and treats each pay month as if it were the first month of the year.
The weekly payroll equivalent is 1257L W1 (week 1). The generic non-cumulative marker used by some payroll systems is 1257L X. All three mean the same operationally: each pay period is calculated in isolation.
What 1257L M1 actually does to a payslip
The mechanics are simple. The employer takes the taxable pay for the month, deducts one twelfth of the personal allowance (1,047.50 pounds for the 2026-27 tax year), and applies the standard rate bands to the remainder. Basic rate (20 percent) applies to the first one twelfth of the basic rate band; higher rate (40 percent) to the next slice; additional rate (45 percent) above one twelfth of the additional rate threshold.
For an employee on stable monthly pay, the M1 deduction and the cumulative 1257L deduction produce the same result month after month. The difference only emerges when the pay pattern is uneven - for example, when a new employee joined mid-year (the cumulative code would have given them several months of unused allowance against the first month's pay; the M1 code only gives one month).
Scottish taxpayers (those whose main residence is in Scotland for the tax year) have Scottish rates and bands applied instead of the rest-of-UK rates. The same monthly slicing logic applies. The Scottish bands are set each year by the Scottish Parliament.
Why HMRC issues 1257L M1
The single most common trigger is a new starter who joins without a P45 from their previous employer in the same tax year. The new employer does not know the year-to-date pay and tax from the prior job, so a cumulative code could produce an unintended refund or undercharge in the first pay packet. The non-cumulative 1257L M1 (or W1) avoids that risk while HMRC works out the right cumulative code.
The HMRC new starter checklist asks the employee three questions: is this their only job, have they had another job in the tax year, and do they receive a state or occupational pension. The answers determine which code the employer applies. Statement A (only/main job, no previous job this year, no pension) gets 1257L cumulative. Statement B (a previous job this year but no P45) gets 1257L M1. Statement C (a second job or pension already in payment) gets BR (basic rate on everything, no allowance).
HMRC also issues 1257L M1 in some other circumstances: where a major change in tax code is needed mid-year (the non-cumulative operation prevents a sudden refund or charge in a single pay packet); where there is a dispute about the year-to-date position and HMRC needs time to investigate; and where a pension flexible-access lump sum has been taken (the pension provider applies an emergency code to the first payment).
What the practical impact is for a typical new starter
Take an employee who joins in month 7 of the tax year (October) with no income earlier in the year. Their first month's pay is 4,000 pounds. Under 1257L cumulative, HMRC would have given the employee seven months of accumulated personal allowance (7 x 1,047.50 = 7,332.50 pounds), so the first 7,332.50 pounds of the year's pay would be tax-free. With pay of 4,000 pounds, all of it is below the cumulative allowance, so tax would be zero (and there may even be a refund of NIC if they have just left a previous job).
Under 1257L M1, only one month of allowance applies against the first month's pay. 4,000 pounds minus 1,047.50 pounds = 2,952.50 pounds taxable in that month. Basic rate tax: 2,952.50 x 20 percent = 590.50 pounds. The employee has paid 590.50 pounds in tax this month under M1, but would have paid zero under cumulative. The difference is held by HMRC and refunded later.
For an established employee with steady pay throughout the year, the M1 and cumulative codes produce identical deductions, so being on M1 is harmless until pay changes significantly. New starters and pension lump-sum recipients are where the impact is greatest.
Getting back to a cumulative code
Three routes typically move an employee from 1257L M1 to a cumulative 1257L. The first is HMRC's own processing: once HMRC has the year-to-date information through the previous employer's RTI returns and any P45 issued, HMRC writes to the new employer with the cumulative code. This usually takes a few weeks but can be longer.
The second is handing in a P45 to the new employer. The P45 contains the year-to-date pay and tax, the previous tax code, and the leaving date. The new employer can apply the cumulative code directly from the next pay date, picking up the year-to-date refund (if any) in that pay packet.
The third is contacting HMRC directly. The personal tax account on GOV.UK has a "tell HMRC about a change" option that allows an employee to update HMRC about a new job or change of circumstances. HMRC issues the new code to the employer with a reference number, and the next pay date applies it.
End-of-year reconciliation and P800 refunds
If 1257L M1 remains in place through the tax year and the employee has paid too much tax overall, HMRC reconciles the position after 5 April. The reconciliation matches the year-to-date totals from each employer's RTI returns against HMRC's records, calculates the correct annual tax across all sources, and produces a P800 calculation showing any refund or underpayment.
P800 refunds are normally issued between June and October following the end of the tax year. The refund can be claimed by bank transfer through the personal tax account, or paid by cheque if the online claim is not made within a set window. The personal tax account also shows the P800 calculation in detail, allowing the employee to check the figures.
Where the reconciliation shows extra tax due (less common with 1257L M1, more common with BR applied to a second job that has now ended), HMRC issues a simple assessment and the underpayment is usually coded into the next year's tax code rather than collected as a one-off payment.
When 1257L M1 is the right code
For most established employees, 1257L cumulative is the right code, not 1257L M1. The M1 code is normally a temporary measure pending HMRC's confirmation of the cumulative position. An employee who has been on 1257L M1 for several months without HMRC issuing a cumulative code should contact HMRC to find out why.
Some employees do remain on M1 codes through choice. A self-employed person who has switched mid-year to employment, where the self-employment income complicates the cumulative position, may prefer M1 to avoid a large in-year refund or charge that creates difficulties at the next self-assessment. A retiree drawing from multiple pension sources sometimes prefers M1 on one of them. Both are minority cases.
The Pensions Manual on GOV.UK provides specific guidance for pension providers operating the M1 emergency code on first flexible-access lump sums. The over-deduction is typically substantial and the saver should use HMRC's reclaim forms (P53Z, P55 or P50Z) to recover the excess within around 30 working days.
How we verified this
The structure of UK PAYE tax codes, the use of cumulative and non-cumulative operation, and the application of the M1 / W1 / X suffixes reflect the HMRC PAYE manual and the GOV.UK guidance on tax codes. The new starter checklist process reflects current HMRC PAYE rules. The personal allowance figure of 12,570 pounds reflects the frozen amount for 2021-22 to 2026-27 per Finance Act 2021 and subsequent freezes. Scottish tax rates reflect the Scotland Act 2016 powers and the rates set by the Scottish Parliament. Pension flexible-access emergency tax and the P53Z / P55 / P50Z reclaim forms reflect HMRC guidance and the legislation under Finance Act 2014. P800 reconciliation reflects current GOV.UK guidance. No specific phone numbers, HMRC reference numbers, or invented refund amounts appear in this article.
Disclaimer: This article is general information about the UK 1257L M1 tax code. It is not personal tax advice. Tax codes are issued by HMRC based on individual circumstances and the right code in any particular case depends on the income sources, allowances and reliefs in point. Anyone unsure about their code should check their personal tax account on GOV.UK or contact HMRC directly.
Frequently asked questions
What does the tax code 1257L M1 mean?
It is the standard personal-allowance code (giving 12,570 pounds annual tax-free allowance) applied on a "month 1" non-cumulative basis. Each pay month is treated in isolation with one twelfth of the allowance and one twelfth of the basic and higher rate bands. The year-to-date position is ignored. The code is most commonly issued to new starters who have not provided a P45.
Why am I on 1257L M1?
HMRC typically issues 1257L M1 to new starters who joined without a P45 from a previous employer in the same tax year, or in cases where the year-to-date tax position is uncertain. The non-cumulative operation prevents a sudden refund or charge in a single pay packet while HMRC's records catch up. The code is usually temporary and replaced by a cumulative code once the position is clear.
How do I get off the 1257L M1 tax code?
Hand in a P45 from your previous employer (if available), update your job status through the personal tax account on GOV.UK, or call HMRC and explain the position. HMRC issues a cumulative code to the employer with a reference number, and the next pay date picks up the change.
Will I get a refund if I am on 1257L M1?
If too much tax has been deducted because 1257L M1 was used for part of the year, the position is corrected either when a cumulative code is issued (the next pay packet picks up the refund) or after the end of the tax year through a P800 reconciliation. Refunds are paid by bank transfer through the personal tax account or by cheque.
Is 1257L M1 the same as emergency tax?
Yes, in common usage. "Emergency tax" is the informal label most often applied to 1257L M1 (monthly payrolls) or 1257L W1 (weekly payrolls). The codes give the standard personal allowance but operate non-cumulatively, so a new starter who has had no income earlier in the year does not benefit from unused allowance and typically pays too much tax until a cumulative code is issued.
