A 125L M1 tax code tells your employer that you’re entitled to just £1,250 of tax-free pay for the year and that each pay period should be taxed on its own, with no reference to what you’ve already earned or paid since 6 April. That £1,250 figure sits far below the standard £12,570 personal allowance, so you’re almost certainly having too much tax taken from every payslip. In most cases the code is temporary, and anything you’ve overpaid can be reclaimed.
What the Number and Letter Mean
Every PAYE code has a number and a letter. The number is your annual tax-free allowance with the last digit removed, so 125 means £1,250 and the standard 1257 means £12,570.1GOV.UK. Tax Codes: What Your Tax Code Means Your employer spreads that figure across your pay periods to work out how much of each paycheck is free of tax.
The L says you qualify for the standard personal allowance category. It doesn’t confirm the amount. The amount has already been reduced by something else, which is why the number reads 125 rather than 1257.2GOV.UK. Understanding Your Employees Tax Codes – What the Letters Mean
What the M1 Suffix Does
M1 stands for “Month 1.” It tells your employer to treat every month as though it were the first month of the tax year. Weekly-paid employees see W1 instead, working the same way on a weekly cycle.3GOV.UK. Tax Codes: Emergency Tax Codes
A normal cumulative code tracks your total pay and total tax since 6 April and rebalances each period, so an overpayment in one month is automatically corrected in the next. M1 turns that off. Each month stands alone. If you overpaid in April and May, your June payslip won’t repay you. While M1 remains in place, your employer cannot refund earlier overpayments through payroll.
In practice, a 125L M1 code gives you about £104 of tax-free pay each month, with everything above taxed at the basic 20% rate (and higher rates where they apply), as though you earn the same amount every month of the year. For most people this pulls significantly more tax than a cumulative code would.
Why Your Allowance Dropped to £1,250
Something has reduced the £12,570 standard allowance by £11,320. A handful of situations can produce a cut that size.
Taxable Employment Benefits
Company perks like a car or private medical insurance count as taxable income, and HMRC collects the tax by trimming your allowance. A company car benefit valued at £3,180, for example, drops the allowance to £9,390 and produces a 939L code.1GOV.UK. Tax Codes: What Your Tax Code Means Stack enough benefits and the number can fall as far as 125.
Unpaid Tax From a Previous Year
If you underpaid tax in an earlier year, HMRC often collects the shortfall by reducing this year’s allowance rather than billing you separately. A large underpayment can cut the code sharply.
Income Over £100,000
Once your adjusted net income passes £100,000, the personal allowance shrinks by £1 for every £2 above that threshold, reaching zero at £125,140.4GOV.UK. Income Tax Rates and Personal Allowances An allowance of £1,250 corresponds to estimated income of roughly £122,640. If HMRC is working from incomplete information about your earnings, it can land on a figure in that range even when your actual income turns out to be different.
Allowance Split Across Two Jobs
If you have more than one job, HMRC usually gives your full allowance to your main employer and a code such as BR to the second. You can ask HMRC to split the allowance between employers, and if the split is uneven one job might carry a 125L code.
What Commonly Triggers This Code
Starting a new job is the most frequent cause. If you don’t hand your new employer a P45 from your previous role, they have no record of your pay and tax so far this year, and HMRC applies an emergency code until it can verify your details.3GOV.UK. Tax Codes: Emergency Tax Codes Without a P45 your employer will ask you to complete a starter checklist, and depending on the statement you pick HMRC may apply a reduced allowance on a non-cumulative basis.5GOV.UK. Starter Checklist if Youre Starting a New Job
Pension withdrawals are another trigger, and this is where M1 bites hardest. A single large lump sum can be taxed as though you’ll take that amount every month, pushing income into higher rate bands that don’t actually apply over the full year.
Benefits that change mid-year can also do it. When HMRC updates your code partway through the year to reflect a new benefit, they sometimes apply it non-cumulatively to avoid a large one-off adjustment in a single pay period.
How to Get the Code Corrected
Before you contact HMRC, have your National Insurance number, the PAYE reference from the top of your payslip, and an estimate of your total income for the year from all sources. If you have a P45 from a previous job and haven’t given it to your current employer, do that first: it often clears the emergency code on its own.6GOV.UK. Your P45, P60 and P11D Form
The quickest route is the Check your Income Tax service on GOV.UK, which shows your current code, the income HMRC thinks you’re earning, and lets you update your details.7GOV.UK. Check Your Income Tax for the Current Year You’ll need a GOV.UK One Login or Government Gateway account, and setting up One Login for the first time requires a valid photo ID such as a UK passport or photocard driving licence.8GOV.UK. Proving Your Identity With GOV.UK One Login
To speak to someone, the income tax helpline is 0300 200 3300, open Monday to Friday from 8am to 6pm and closed on bank holidays.9GOV.UK. Income Tax: Enquiries Expect a wait. Once HMRC updates your code they send a P6 notice to your employer, who applies the new code from your next pay run.10GOV.UK. Understanding Your Employees Tax Codes – Changes During the Tax Year Most changes take effect within one or two pay cycles.
Reclaiming Tax You’ve Overpaid
If you’ve spent several months on a 125L M1 code, you’ve most likely overpaid. The money comes back in one of two ways.
The simpler route is automatic correction within the tax year. When HMRC issues a cumulative code to your employer, the next payroll run recalculates your position for the whole year in one go, and any refund is added to that paycheck. The payment can be noticeably larger than usual for that single period.
If the overpayment sat in a tax year that has already ended, HMRC sends a P800 tax calculation, usually between June and March of the following year.11GOV.UK. Tax Overpayments and Underpayments The letter shows whether you overpaid or underpaid. If you’re owed money you can claim online through your personal tax account, and the refund usually arrives within five working days. A cheque takes longer. If you haven’t received a P800 but believe your tax was wrong, you can contact HMRC directly and ask them to review the year.
You have four tax years from the end of the year in which the overpayment happened to make a claim. The deadline to claim for the 2021/22 tax year, which ended on 5 April 2022, is 5 April 2026. After the window closes, HMRC treats the year as finalised and won’t reopen it, so if you suspect an incorrect code in a recent year it’s worth checking soon.