Think your tax code is wrong? How to spot a wrong tax code, fix it with HMRC, and claim any refund you are owed in the 2026/27 tax year.
If you think your tax code is wrong, you are probably right to check. A wrong tax code is one of the most common payroll problems in the UK, and most people only notice it when their take-home pay drops for no obvious reason.
Here is the reassuring part: fixing a wrong tax code is usually quick, and if you have overpaid, HMRC gives the money back. This guide covers how to tell whether your code is actually wrong, the exact steps to fix it, and when you will see any refund land.
A wrong tax code means HMRC has told your employer to tax you against the wrong tax-free allowance, so you are either paying too much tax right now or quietly building up a bill for later.
Your code is shorthand for how much you can earn before income tax starts. The standard code is 1257L, which protects the first £12,570 of your pay each year (the personal allowance divided by ten, with L for the standard allowance). When the number is too low, or the letters are wrong for your situation, the maths comes out wrong and your payslip pays for it.
The fastest check takes two minutes. Open the HMRC app or your Personal Tax Account at gov.uk, find your current code, and compare it with the code printed on your latest payslip. If they match, your employer is using the right instruction. If they disagree, your employer’s payroll is running on stale data and that is your problem to flag.
There are three classic signs of a wrong tax code:
1257L and you have one job, no company car, and no tax debt you know about.A worked example shows why this matters. Say you earn £28,000 a year and your employer has you on a BR code by mistake (BR taxes every pound at the basic 20% rate with no personal allowance, which is correct for some second jobs but not for a main job). On the right code you would get £12,570 tax-free. On BR you do not, so you overpay 20% of £12,570, which is £2,514 across the year, or roughly £209 a month. That is real money sitting in the wrong place because of one mistaken code.
Not every odd-looking code is a mistake. A few are temporary or correct by design.
If you started a new job and your employer did not get your P45 in time, you might see 1257L W1 or 1257L M1. The W1 or M1 part means the code is non-cumulative, so payroll treats each pay period as if it is the first of the year. You often overpay for a month or two, then HMRC reconciles it and the extra comes back. This usually sorts itself out, so give it a pay cycle before acting.
A BR, D0, or 0T code on a second job is frequently correct, because your personal allowance is already being used by your main job. The same code on your only job is a red flag. And a K code, which adds to your taxable pay rather than protecting part of it, is right when you have benefits in kind or owe tax from a previous year, but wrong if none of that applies to you. If you cannot explain why your code is not the standard 1257L, that is your cue to dig in. Our guide on what 1257L actually means is a useful baseline.
Here is what I would do, in order, to fix it without wasting an afternoon on hold.
Step 1: confirm the code HMRC holds. Log into the HMRC app with your Government Gateway ID and read your current tax code and the income figures HMRC has on file. Most wrong codes trace back to HMRC holding outdated information about your jobs, benefits, or estimated pay.
Step 2: correct your details online. In the app or your Personal Tax Account you can update your employment, remove a job you have left, or fix an estimated salary that is too high or too low. When you change these, HMRC recalculates your code and sends a fresh instruction to your employer automatically. For most people this is the whole fix, and it is the fastest way to change your tax code.
Step 3: call HMRC if the online route will not cover it. Some situations, like an incorrect benefit-in-kind charge or a code error you cannot trace, need a person. Ring the income tax helpline on 0300 200 3300 with your National Insurance number ready. Phone is slower to reach but better for anything the app will not let you edit.
Step 4: check your next payslip. Once HMRC issues the corrected code, your employer applies it on the next pay run. Confirm the new code appears on your payslip. If your payslip still shows the old code two pay periods later, chase your payroll team, because the holdup is now on their side rather than HMRC’s.
You almost never fix this by asking your employer to change the number themselves. Employers apply whatever code HMRC sends, so the correction has to start with HMRC. If you want to sense-check your code before you call, the steps in our verify your tax code guide walk through every place it appears.
If a wrong tax code made you overpay, the refund depends on which tax year it happened in.
For the current 2026/27 tax year, the money usually comes back through your payslip. Once the corrected, cumulative code lands, payroll compares the tax you have paid so far against what you actually owe and adjusts the next payment. You might see a smaller deduction, or an outright credit, on your following payslip or two.
For a previous tax year, HMRC reconciles after the year ends and sends a P800 tax calculation. If you are owed money, the P800 tells you how to claim it, often with an option to receive it straight to your bank account through your online account, or by cheque if you do nothing. P800 refunds can take a few weeks, so it is worth claiming online rather than waiting for the post.
One thing worth knowing: you do not get a refund just because your code was wrong. You get one because the wrong code made you pay more than you owed. If the wrong code meant you paid too little, the correction works the other way, and HMRC will collect the shortfall, usually by adjusting next year’s code.
The personal allowance is still £12,570 for the 2026/27 tax year. It has been frozen since 2021 and is currently set to stay frozen until April 2028, so the standard 1257L code and the maths behind it have not moved. The higher-rate threshold is still £50,270.
What did change is how HMRC tells you about code updates. From April 2026, most P2 coding notices went digital-first, so instead of a letter through the door you find the update in your HMRC online account. That is why some people saw their code shift in April with no warning and assumed something had gone wrong. Often it had not, but the only way to be sure is to look. If your spring 2026 payslips looked different and you never got a letter, check the app for a new notice before you assume the worst.
1257L with no company car, second job, or tax debt are the ones worth questioning.If you want to see what your take-home pay should look like on the right code, the NetPay app runs the full calculation for you, including income tax, National Insurance, pension, and student loan, so a coding error has nowhere to hide. Free to download.
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Compare the code on your payslip with the one HMRC shows in the HMRC app or your Personal Tax Account. If they disagree, or if you are on a code lower than 1257L with no company car, no second job, and no tax debt, your tax code is probably wrong. A sudden drop in take-home pay with no pay change is the most common warning sign.
Update your income and employment details in the HMRC app or your Personal Tax Account, or call HMRC on 0300 200 3300. HMRC issues a corrected code to your employer, usually within a few days, and your next payslip uses it. You rarely need to involve your employer directly, since the code comes from HMRC.
Yes, if a wrong tax code made you overpay. Within the same tax year the refund usually comes back automatically through your payslip once the corrected code lands. For previous tax years HMRC sends a P800 calculation and pays the refund by bank transfer or cheque.
Once you have updated your details or spoken to HMRC, a new code normally reaches your employer within about a week, and your following pay run applies it. Refunds for the current year follow on the next payslip or two. Previous-year refunds via P800 can take several weeks.
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A note on financial advice: NetPay UK calculates take-home pay based on official HMRC tax rules. This article reflects rules in force at the time of publication (11 June 2026). Tax rules change. For complex situations, consult a qualified UK accountant or visit gov.uk/income-tax.
