TL;DR: The 1257L M1 tax code is the standard personal-allowance code (1257L gives an annual tax-free 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 fresh slice in isolation, ignoring the year-to-date tax position. HMRC issues 1257L M1 (and the weekly equivalent 1257L W1) most commonly to new starters who do not have a P45 from a prior employer in the same tax year, or to taxpayers whose year-to-date position is uncertain. The code is often called "emergency tax" because it usually produces too much tax compared with a cumulative calculation. HMRC normally reconciles the position at the end of the tax year, with any overpayment refunded through a P800 or directly through payroll once a cumulative code is applied.
Last reviewed May 2026
UK PAYE tax codes have three parts: a number (the tax-free amount divided by 10), a letter (the category code), and (where applicable) an operating-basis suffix telling the employer how to apply the code. 1257L M1 is a common combination: the standard personal allowance code, operated month by month rather than cumulatively across the tax year.
This guide explains exactly what the 1257L M1 code does, why HMRC issues it, how it affects the monthly tax deduction, how to get back to a normal cumulative code, and how the position is reconciled at the end of the tax year.
What 1257L means before the M1 suffix
1257L is the standard tax code for most UK working-age employees. The 1257 represents the annual tax-free personal allowance of 12,570 pounds (1257 times 10). The "L" suffix means the taxpayer is entitled to the standard personal allowance for the tax year. The 1257L code has been the standard since the personal allowance was frozen at 12,570 pounds for 2021-22 and subsequent years.
Under a normal 1257L code operated cumulatively, the employer recalculates the year-to-date tax position at each pay date. The cumulative calculation spreads the tax-free 12,570 pounds evenly across the year (1,047.50 pounds a month, or 241.83 pounds a week), and adjusts for any earlier overpayment or underpayment in the year.
For a typical employee with steady monthly pay, the cumulative and non-cumulative monthly tax deductions are identical. The two diverge when there is a gap (a month with no pay, a new starter in mid-year, a code change part-way through the year, or significant variable pay), at which point the cumulative code recalculates against the full year while the non-cumulative code does not.
The M1 suffix and what it changes
The M1 (month 1) suffix tells the employer to treat each pay month as if it were the first month of the year. The full monthly slice of the personal allowance (1,047.50 pounds) is given against the current month's pay only; the year-to-date position is ignored. The same logic applies to W1 (week 1) on weekly payrolls and to X (a generic non-cumulative indicator).
The practical effect is that the employee receives no benefit from any unused personal allowance from earlier in the tax year. A new starter who joins in month 6 with no income earlier in the year would, on a cumulative 1257L code, get six months of personal allowance applied against the first month's pay (producing a small refund or zero tax). On 1257L M1, only one month of allowance applies against the first month's pay.
The same principle works in reverse. An employee who has had high pay earlier in the year and then drops to lower pay on a 1257L M1 code receives full one-month allowance against the new lower pay each month, even though the earlier high pay may already have used up the year's allowance and a cumulative code would now produce no allowance at all. This rarely causes problems in practice because lenders and HMRC tend to use cumulative codes for established employments.
Why HMRC issues 1257L M1
The most common reason is a new starter who joins without a P45 from their prior employer in the same tax year. The new employer does not know the year-to-date pay and tax from the earlier job, so applying a cumulative code could produce an unintended refund or undercharge. The non-cumulative 1257L M1 (or W1) avoids this risk while HMRC works out the right code.
The HMRC new starter checklist asks the employee whether the new job is their only job, whether they have had another job in the tax year, and whether they receive a state or occupational pension. The answers (statements A, B and C on the older checklist, or the modern equivalent) drive which code the employer applies pending HMRC confirmation. Statement B (a previous job in the tax year, but no P45) normally produces 1257L M1.
HMRC also issues 1257L M1 in some cases where the cumulative position is uncertain due to a tax code change. The non-cumulative operation prevents a sudden refund or charge in a single pay packet while HMRC confirms the right cumulative position. Once HMRC's records catch up with the employee's actual circumstances, a cumulative code is normally issued.
How the monthly tax deduction works under 1257L M1
Under 1257L M1, the monthly tax deduction is calculated as follows. The employer takes the taxable pay for the month, subtracts 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 up to one twelfth of the basic rate band, higher rate (40 percent) applies to the next slice, and additional rate (45 percent) applies above one twelfth of the additional rate threshold.
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 under the Scotland Act 2016 powers.
National Insurance is calculated separately from income tax, against NIC thresholds for each pay period, and is not affected by the tax code suffix. The NIC line on the payslip is the same under 1257L M1 as under 1257L cumulative.
Getting back to a cumulative code
Three routes typically move an employee from 1257L M1 (or W1) to a cumulative 1257L. The first is HMRC's own processing: once HMRC has the year-to-date information from the employee's previous employer (through the prior employer's RTI submission and any P45 issued), HMRC issues the cumulative code to the new employer. This is the standard route and usually takes a few weeks.
The second is handing in a P45 to the new employer. The P45 contains the year-to-date pay and tax figures from the prior job, the tax code in operation at leaving, and the leaving date. The new employer can apply the cumulative code directly from the next pay date, picking up any year-to-date overpayment in the next pay packet.
The third is contacting HMRC directly through the personal tax account on GOV.UK or by telephone, explaining the position and asking for a cumulative code to be issued. This is the fastest route where the prior job has ended and the P45 is not available. HMRC issues the new code to the employer with a reference number.
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 (the typical outcome for someone who joined in mid-year on this code), 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.
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 claim is not made online within a set period. Where the reconciliation shows extra tax due (less common with 1257L M1), HMRC issues a simple assessment and the underpayment can be coded into a future year's tax code.
End-of-year reconciliation is the safety net, but it does not avoid the cash-flow cost of having too much tax taken out across the year. Switching to a cumulative code mid-year produces the year-to-date refund in the next pay packet, which is much faster than waiting for a P800.
How we verified this
The structure of UK 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 for employees and employers. The new starter checklist and P45 processes reflect current HMRC PAYE rules. The end-of-year reconciliation through P800 and simple assessment is set out in current GOV.UK guidance. Scottish tax rates and bands reflect the powers under the Scotland Act 2016 and the rates set by the Scottish Parliament. Specific figures and procedures should be reconfirmed on GOV.UK for the relevant tax year.
Disclaimer: This article is general information about UK PAYE tax codes. It is not personal tax advice. Tax codes are set by HMRC based on individual circumstances and the right answer in an individual case depends on the specific income sources, allowances and reliefs that apply. Anyone unsure about their code should check their personal tax account on GOV.UK or contact HMRC directly.
Frequently asked questions
What does the 1257L M1 tax code mean?
1257L M1 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 personal allowance and the basic and higher rate bands applied to that month's pay. The year-to-date position is ignored. The code is often issued to new starters without a P45 or where HMRC is uncertain of the year-to-date position.
Why am I on a 1257L M1 tax code?
HMRC typically issues 1257L M1 (or 1257L W1 on weekly payrolls) to new starters who joined without a P45 from a prior employer in the same tax year, or in cases where the year-to-date tax position is uncertain. The non-cumulative operation prevents a 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 a prior employer (if available), check the personal tax account on GOV.UK and use the "tell HMRC about a change" option, or call HMRC and explain the position. HMRC issues a cumulative code to the employer with a reference number. The next pay date typically applies the new code and produces any year-to-date refund.
Will I get a refund if I am on 1257L M1?
If too much tax has been paid because 1257L M1 has been used for part of the year, the position is corrected either when a cumulative code is issued (the next pay date picks up the refund) or after the end of the tax year through a P800 reconciliation. Refunds are normally paid by bank transfer through the personal tax account or by cheque.
Is 1257L M1 the same as emergency tax?
"Emergency tax" is an informal term that most commonly refers to 1257L W1 or 1257L M1 codes. The codes give the standard personal allowance but operate non-cumulatively, so a new starter who has had no income earlier in the tax year does not benefit from any unused allowance and may pay too much tax. The code is corrected once a cumulative code is issued or at the end-of-year reconciliation.
