A BR M1 tax code means every pound you earn from that job or pension is taxed at the basic rate of 20%, with no personal allowance applied, and each pay period is calculated in isolation instead of running a year-to-date total.1GOV.UK. Tax Codes – What Your Tax Code Means It is almost always temporary. HMRC uses it when it does not yet have enough information to give you the right code, or when your personal allowance is already being used against another source of income. Most people on BR M1 end up overpaying tax and can reclaim the difference once their records are put right.
What the BR Part Does to Your Pay
BR stands for basic rate. It tells your employer or pension provider to deduct income tax at 20% from everything paid through that source, starting from the very first penny.2GOV.UK. Income Tax Rates and Personal Allowances The first £12,570 of annual income is normally tax-free under the personal allowance. A BR code strips that away for the income it applies to, on the assumption that you are already receiving the allowance elsewhere.
The maths is blunt. Earn £2,000 in a month from a second job coded BR, and exactly £400 goes to income tax. No threshold to reach, no sliding scale, and no higher-rate band unless your combined income across all sources pushes you above £50,270 for the year, at which point a different code would be needed.2GOV.UK. Income Tax Rates and Personal Allowances
What the M1 Part Changes
The M1 suffix means “Month 1.” Payroll software is told to treat every month as though it were the first month of the tax year.3GOV.UK. Emergency Tax Codes Under a normal cumulative code, your employer keeps a running total of what you have earned and paid so far, so an overpayment in one month gets ironed out the next. M1 switches that off. Each month is sealed, with no memory of what came before.
The knock-on effect is that in-year refunds through payroll are blocked. If your circumstances shift mid-year and you are owed money, you will not see it drift back through your payslips the way a cumulative code would deliver it. You will typically wait until HMRC issues a new code or until the end-of-year reconciliation picks up the overpayment.
Some payslips print “NONCUM” instead of M1. Same meaning.3GOV.UK. Emergency Tax Codes W1 is the weekly-paid equivalent, and X is used when pay dates vary.
Why You Might Be on BR M1
Three situations account for most cases.
A Second Job or an Additional Pension
The most common reason: more than one source of PAYE income. Your £12,570 allowance is already allocated to your main employer or pension provider, so HMRC instructs the second source to tax everything at basic rate.1GOV.UK. Tax Codes – What Your Tax Code Means If that genuinely reflects your setup, the BR part is correct. The M1 suffix should drop off once HMRC has confirmed all your income details.
Starting a New Job Without a P45
If you start a job without handing over a P45 from your previous employer, the new employer has no idea what you have already earned or paid this year. HMRC applies BR M1 as a holding pattern until the information arrives.3GOV.UK. Emergency Tax Codes Fill in the starter checklist your employer should give you. It asks for your National Insurance number, any other jobs or pensions, and student loan details, and the answers help HMRC assign the right code faster.4GOV.UK. Starter Checklist
Incomplete HMRC Records
Sometimes the gap is on HMRC’s side. If a previous employer’s data has not been reported, or if benefit information from the Department for Work and Pensions has not been linked, HMRC may default to BR M1 as a precaution to prevent an underpayment building up.
What the Deductions Actually Look Like
Income tax at 20% is only one line on the payslip. National Insurance is calculated separately and does not depend on your tax code. For 2025/26, employees pay 8% on earnings between £242.01 and £967 a week (£1,048.01 to £4,189 a month), and 2% above that.5GOV.UK. National Insurance Rates and Categories – Contribution Rates Student loan repayments, where they apply, come off the same payroll run.
Take a £2,000 monthly pay packet under BR M1: £400 to income tax, roughly £76 to National Insurance (8% of the amount above the £1,048 monthly primary threshold), and potentially a further chunk to student loan repayments. That is a noticeably heavier set of deductions than someone on a standard 1257L code would see on the same earnings.
If You Live in Scotland or Wales
Scottish taxpayers see an “S” prefix, so the Scottish version of this code is SBR M1. The Scottish basic rate is also 20%, but Scotland sets its own income bands, which can affect how the year’s tax adds up overall.1GOV.UK. Tax Codes – What Your Tax Code Means Welsh taxpayers see a “C” prefix, though Welsh rates currently match those of England and Northern Ireland.
How to Check and Correct the Code
The fastest route is the “Check your Income Tax” service on GOV.UK, part of your personal tax account.6GOV.UK. Check Your Income Tax for the Current Year Sign in, update your income details from jobs and pensions, and see what HMRC currently holds on file. Correcting out-of-date figures through the portal often triggers an automatic review.
If you would rather talk to someone, the HMRC Income Tax helpline is 0300 200 3300, Monday to Friday, 8am to 6pm.7GOV.UK. Income Tax – Enquiries Have your National Insurance number, your employer’s PAYE reference (top of the payslip), and a recent P45 or P60 ready. The representative can see your record and either update the code on the spot or flag it for review.
Whichever route you take, the aim is the same: give HMRC an accurate picture of your total annual income from every source. Once it has that, it can decide whether BR still fits, whether you need a full personal allowance moved across, or whether the allowance should be split between jobs.
What Happens After the Code Is Updated
HMRC sends two notices once the change is processed. Your employer receives a P6 form with your new code.8GOV.UK. Understanding Your Employees Tax Codes – Changes During the Tax Year You receive a P2 coding notice by post or through your personal tax account, showing the new code and how it was worked out. HMRC aims to send both within 15 working days of the change being agreed.9GOV.UK. Tax Codes – If You Think Your Tax Code Is Wrong
After that, the timing depends on your pay cycle. Monthly-paid employees should see the new code on the next payslip or the one after. Weekly-paid employees should see it by the third payslip after the employer receives the P6.9GOV.UK. Tax Codes – If You Think Your Tax Code Is Wrong If the replacement code is cumulative rather than M1, payroll will automatically recalculate your year-to-date position and may refund overpaid tax in that same pay packet.
Reclaiming Overpaid Tax
If you have been on BR M1 for several months and then move to a corrected cumulative code, payroll usually sorts the refund automatically by recalculating from the start of the tax year. Check the numbers on the payslip, but there is normally nothing more to do.
If the tax year ends before your code is corrected, HMRC runs an automatic reconciliation. Between June and the following March, it compares what you actually earned against what you paid and issues either a P800 tax calculation or a Simple Assessment letter.10GOV.UK. Tax Overpayments and Underpayments If you overpaid, the P800 shows the amount and offers an online refund claim. HMRC says most online claims are paid within five working days; postal claims take longer.
If you think you have overpaid and no P800 arrives, start a claim yourself through the tool at gov.uk/claim-tax-refund.11GOV.UK. Check How to Claim a Tax Refund It asks a series of questions and directs you to the right process. The money does not expire, but HMRC will not chase you down for it either.
When BR M1 Leaves You Underpaid Instead
BR M1 is designed to avoid underpayments, and for most basic-rate earners it does. It can still leave you short if your combined income across jobs pushes you into the higher-rate band above £50,270 and neither employer was deducting at 40%. In that case, the P800 will show tax owed rather than a refund.10GOV.UK. Tax Overpayments and Underpayments
For debts under £3,000, HMRC usually collects by adjusting your tax code the following year rather than demanding a lump sum. Larger amounts have to be paid directly. Getting an incorrect code fixed promptly is the single best way to stay clear of either outcome.