Tax code 1257L M1 gives you the standard £12,570 tax-free Personal Allowance, but on an emergency, non-cumulative basis: each pay period is taxed in isolation, with no reference to what you earned or paid earlier in the tax year. The “1257” is your annual tax-free amount with the last digit dropped, “L” confirms you’re entitled to the standard allowance, and “M1” tells payroll to treat every month as if it were the first month of the tax year. Most people end up on this code after starting a new job without handing in a P45, and it typically means paying a little more tax than you should until HMRC updates your record.
What Each Part of the Code Means
The 1257 corresponds to the £12,570 Personal Allowance set under Section 35 of the Income Tax Act 2007, which the government has frozen at that level through at least April 2031.1GOV.UK. Income Tax: Maintaining the Personal Allowance and the Basic Rate Limit for Income Tax HMRC removes the final digit when constructing the code, so £12,570 becomes 1257.
The “L” signals that you get the standard Personal Allowance with no special adjustments.2GOV.UK. What Your Tax Code Means If HMRC had reduced your allowance, say to recover a previous underpayment or to account for untaxed benefits, the number would be lower or the letter would change.
The “M1” suffix is what makes this an emergency code. It stands for Month 1 and tells payroll software to work on a non-cumulative basis.3GOV.UK. Emergency Tax Codes If you’re paid weekly, the equivalent suffix is W1. Same mechanism, different pay frequency.
Why You’ve Been Put on It
The usual trigger is starting a new job without giving your employer a P45 from your last one. Without that document, the new employer has no record of what you’ve earned or paid in tax so far in the year, and HMRC defaults to the emergency code.3GOV.UK. Emergency Tax Codes
What actually gets you 1257L M1 specifically is the answer you gave on the starter checklist. The checklist has three statements:
- Statement A says this is your first job since 6 April and you haven’t received Jobseeker’s Allowance, Employment and Support Allowance, or Incapacity Benefit. This produces the cumulative 1257L (no M1).
- Statement B says you’ve had another job since 6 April but don’t have a P45, or you’ve received one of those benefits. This is the statement that produces 1257L M1.
- Statement C says you have another job or receive a pension. This typically produces a BR code, taxing all income at 20%.
Ticking the wrong statement is a common mistake. If this really is your only job and you haven’t claimed the listed benefits since April, Statement A is the right answer and skips the emergency code entirely.4GOV.UK. Starter Checklist for PAYE
What It Costs You Each Month
Under a cumulative code, payroll tracks everything you’ve earned since 6 April and matches it against your year-to-date allowance. Unused allowance from earlier months carries forward. Under M1, that doesn’t happen. Each pay period stands alone.
For a monthly earner, the software divides £12,570 by 12, giving £1,047.50 of tax-free pay each month. Anything above that is taxed at the 20% basic rate for that month.3GOV.UK. Emergency Tax Codes Earn £3,000, and £1,952.50 is taxable, so the deduction is £390.50.
The problem shows up if you haven’t worked the full year. Someone starting in October has six months of unused allowance sitting there, roughly £6,285. A cumulative code would apply that against current earnings. M1 ignores it. You get the same £1,047.50 monthly slice as someone who’s been working since April, which almost always means overpaying until the code is fixed.
Bonuses Take a Bigger Hit
One-off payments are worse under M1. A £2,000 bonus paid on top of a £3,000 monthly salary means the whole £5,000 is measured against that single month’s £1,047.50 allowance. Taxable amount: £3,952.50. A cumulative code would let unused allowance from lighter months soften the blow. M1 doesn’t.
Higher-Rate Earners Get Caught Too
For 2026-27, the first £37,700 of taxable income above the Personal Allowance is taxed at 20%, and income from £50,271 to £125,140 is taxed at 40%.5UK Parliament. Direct Taxes: Rates and Allowances for 2026/27 On a monthly basis, the 40% threshold kicks in once taxable earnings for the month go above roughly £3,141.67. Earn £5,000 in one month and payroll takes 20% on the first slice above your allowance and 40% on the rest, even if your annual salary wouldn’t normally reach the higher band. A cumulative code would smooth this out across the year.
How to Switch to the Correct Code
If you have a P45 from your previous employer and simply forgot to hand it in, give it to your current payroll department. The P45 shows your year-to-date pay and tax, which is exactly what payroll needs to switch you onto a cumulative code.
Otherwise, use the HMRC online service. Sign in to “Check your Income Tax,” review your employment and income details, and correct anything wrong or missing.6GOV.UK. If You Think Your Tax Code Is Wrong You’ll need your National Insurance number, which is on your payslip or P60, and your employer’s PAYE reference number, usually on your payslip or contract.7GOV.UK. Your National Insurance Number
If you can’t use the online service, call the Income Tax helpline on 0300 200 3300 (Monday to Friday, 8am to 6pm).8GOV.UK. Income Tax: Enquiries Have your National Insurance number and payslip in front of you.
Once HMRC processes the change, they send the new code to both you and your employer within 15 working days.6GOV.UK. If You Think Your Tax Code Is Wrong The corrected code should show up on your next or following payslip. When the cumulative code kicks in, payroll recalculates your tax for the year to date, and any overpayment comes back through your wages automatically.
If the Code Is Never Corrected
HMRC catches up after 5 April. Between June and March of the following year, they send out P800 tax calculation letters to anyone who has overpaid or underpaid.9GOV.UK. Tax Overpayments and Underpayments If you’ve overpaid, the P800 explains how to claim, either online or by cheque.
You have four years from the end of the relevant tax year to claim back an overpayment. Miss that window and the year is locked.10Low Incomes Tax Reform Group. Tax Refunds If you were stuck on 1257L M1 during 2026-27, you’d need to claim by 5 April 2031. Fixing it during the tax year is much simpler than chasing a refund years later.
Scottish and Welsh Variants
If you live in Scotland, the code carries an “S” prefix, so you’d see S1257L M1. It works the same way, but tells payroll to apply Scottish income tax rates, which have different bands and can produce a different monthly result. Welsh taxpayers see a “C” prefix (C1257L M1), though Welsh rates currently match the main UK rates.