Are You on the Wrong Tax Code? How to Check (and Claim Back)

Here’s a quick one that takes about five minutes and could put hundreds of pounds back in your pocket.

Every payslip has a little code on it, something like 1257L. Most people never give it a second look. But that code tells your employer how much tax to take off you, and if it’s wrong, you could be overpaying every month without ever knowing.

And it happens more than you’d think. Around five million workers are on the wrong code in any given year. Of the people who found they’d been overcharged, three quarters had overpaid by an average of £689.

First, find your code

Grab your most recent payslip. Your tax code is usually near the top, somewhere close to your National Insurance number. It’ll be a few numbers followed by a letter, and for most people it’s 1257L.

It’s also on your P60 (the summary you get at the end of each tax year) and your P45 (the one you get when you leave a job), if you’d rather check there.

What 1257L means, and why it matters

That number isn’t random. Knock the last digit off and add a zero, and you get your tax-free allowance: the amount you can earn before paying any income tax. So 1257 means £12,570 tax-free, which is the standard amount for the 2026/27 tax year. The L just means you get the normal allowance with nothing unusual going on.

If you’ve got one job, no company perks like a company car, and no tax owed from previous years, your code should be 1257L. If it’s something else, it’s worth understanding why.

The codes worth a second look

A different code isn’t automatically wrong. There are good reasons for some of them. But these are the ones that catch people out:

• 1257L W1, M1 or X. These are emergency codes, usually applied when you start a new job before your details have caught up. They tax each pay packet on its own instead of across the whole year, so you often pay too much. They normally fix themselves, but if one’s been sitting there for more than a couple of months, chase it.
• BR. Every penny from that job taxed at 20%, with no tax-free allowance at all. Fine if it’s genuinely a second job, but wrong if it’s your only one.
• 0T. No tax-free allowance applied at all. Sometimes correct for very high earners, but often a sign your details haven’t reached HMRC.
• D0 or D1. Everything taxed at the higher (40%) or additional (45%) rate. Worth double-checking if that doesn’t match your earnings.
• A K code (the letter comes first, like K475). This one adds to your taxable income rather than giving you an allowance, usually because of a benefit like a company car or tax owed from before. Make sure whatever it’s based on is still actually true.

One quick note. If you live in Scotland your code may start with an S, and in Wales a C. That’s normal, it just tells payroll which set of rates to use.

Check it against the real thing, free from HMRC

This is the part that settles it. HMRC has a free online service called Check your Income Tax for the current year. Log in with your Government Gateway details and it shows you the code HMRC is using and the assumptions behind it: your estimated income, any benefits, anything they think you owe.

If those assumptions don’t match your real life, say a company car you handed back or a second job you’ve left, then your code is wrong, and you can put it right there and then.

You can find it at gov.uk/check-income-tax-current-year, or call HMRC on 0300 200 3300 if you’d rather talk to someone. Have your National Insurance number and a recent payslip handy.

What if you’ve been overpaying?

Here’s the good news. If you’ve paid too much, you get it back. Once HMRC updates your code, an overpayment from earlier in the year often comes back automatically through your next payslip.

And if you’ve been on the wrong code for longer, you can claim back overpaid tax for up to four previous tax years. So this isn’t just about this year. There could be more owed to you than you’d expect.

One last thing worth knowing. HMRC no longer automatically sends out every refund the way it used to. In a lot of cases you now have to actively claim what you’re owed, so it really does pay to check rather than assume it’ll sort itself out.

The five-minute version

1. Find the tax code on your latest payslip.
2. If it’s 1257L and you’ve got one straightforward job, you’re very likely fine.
3. If it’s anything else, log in to HMRC’s free “Check your Income Tax” service and compare it against your real situation.
4. If something doesn’t add up, correct it online or call 0300 200 3300.
5. Any tax you’ve overpaid comes back, and you can go back four years.

Not bad for five minutes with a payslip.

This is general information, not personal tax advice. Everyone’s situation is a little different, so if you’re unsure, HMRC can talk you through your own circumstances.

— Emma