If your tax code looks wrong, you can fix it by signing in to your Personal Tax Account on GOV.UK and updating your details, or by calling HMRC’s Income Tax helpline. The standard code for 2025/26 is 1257L, which reflects the £12,570 Personal Allowance, so a code that doesn’t match your actual circumstances usually means you’re paying too much or too little tax each month.1GOV.UK. Income Tax Rates and Personal Allowances Sort it out quickly and your take-home pay corrects itself through payroll; leave it and you’re waiting on a refund or bill after the tax year ends.
Check Which Code You’re Actually On
Your tax code is printed near the top of your payslip, next to your National Insurance number. You’ll also find it on your P60 (the end-of-year summary your employer gives you each April) or on a P45 from a job you’ve recently left. The most current version is the one HMRC holds on file, which you can see by signing in to your Personal Tax Account and checking the code listed for each of your employments or pensions.2GOV.UK. Check Your Income Tax for the Current Year
If you have one job and no taxable benefits, you’d normally expect 1257L. Anything else is worth a closer look.
What the Numbers and Letters Mean
The number in your code is your tax-free allowance with the last digit dropped, so 1257L points to a £12,570 Personal Allowance.1GOV.UK. Income Tax Rates and Personal Allowances A lower number means something is reducing your allowance, usually a taxable benefit or tax owed from an earlier year. A higher number means you’re getting extra relief on top.
The letter tells the payroll system which rules to apply. L is the standard Personal Allowance. BR taxes every pound from that job or pension at the basic rate of 20%, which typically fits a second job where your allowance is already used elsewhere. 0T applies no allowance at all, often because HMRC lacks information about you. K means your deductions are bigger than your allowance, so extra tax is being added to your pay rather than an allowance subtracted; there is a safeguard that stops your employer taking more than half your pre-tax pay through a K code in any pay period.3GOV.UK. Tax Codes S signals Scottish rates; C signals Welsh rates.
A code that ends in W1, M1, or X is an emergency code, used weekly, monthly, or where pay dates vary.4GOV.UK. Tax Codes – Emergency Tax Codes Emergency codes tax each pay period on its own, ignoring what you’ve earned or paid earlier in the year, so they usually mean you’re being overtaxed until the code is put right.
Common Reasons Your Code Is Wrong
Starting a new job without handing over a P45 is the classic trigger. HMRC has no record of your earnings so far this year, so you’re put on an emergency code and typically overtaxed until the picture catches up. The same happens when a pension starts alongside employment income and HMRC hasn’t been told about the extra source.
Changes to workplace benefits are the other big one. If your employer provides a company car, private medical insurance, or similar perks, HMRC adjusts your code to collect the tax on them. Give the car back, switch to a different one, or lose the private fuel arrangement, and the old adjustment sits there overtaxing you until someone tells HMRC.5GOV.UK. Tax on Company Benefits – Tax on Company Cars
A stale Marriage Allowance transfer can also throw the code off if the original circumstances no longer apply. And sometimes it’s a plain HMRC error based on outdated records or a mix-up between employers.
What to Have Ready Before You Contact HMRC
Have your National Insurance number in front of you; it’s asked for at every stage. Pull out your most recent payslip so you can quote the current tax code and the employer’s PAYE reference, both of which usually appear near the top.
Then think about the substance of the change. For a company car, HMRC needs the list price including VAT, the CO2 emissions figure, and whether a diesel meets Euro 6d standards.6GOV.UK. Check or Update Your Company Car Tax For flat-rate job expenses or professional subscriptions, have the amounts to hand. If you have more than one job or pension, work out a rough total of your annual income across all of them so a new code can be set that accounts for everything.
Report the Error Online or by Phone
Through Your Personal Tax Account
The fastest route is the Check your Income Tax service on GOV.UK. Once signed in, you can see the code HMRC is using, what makes it up, and where any figure looks wrong. From the same screen you can update job and pension income, tell HMRC about changes that affect the code, and correct employer or pension provider details.2GOV.UK. Check Your Income Tax for the Current Year Company car and medical insurance details can be checked or updated the same way.7GOV.UK. Personal Tax Account: Sign In or Set Up
Follow the screens through to the final confirmation. It’s easy to change a figure and close the browser before HMRC actually records the update. The HMRC app does the same job on a phone.
By Calling the Income Tax Helpline
If you’d rather talk to someone, call HMRC’s Income Tax helpline. Automated security questions come first, so have your National Insurance number and personal details to hand, then explain the discrepancy and give the adviser the figures you gathered. They can update the record while you’re on the line, which sends an automatic notification to your employer or pension provider.
Waits are longest at the start of the tax year in April and around the January Self Assessment deadline. Mid-week, mid-morning tends to be quicker.
What Happens After the Correction
HMRC issues a Coding Notice known as a P2, which shows how your new code was worked out, allowance by allowance and deduction by deduction.8HM Revenue and Customs. PAYE Manual – Coding: Codes: How They Are Used and Calculated: P2 Notice of Coding It arrives through your Personal Tax Account or by post. At the same time, HMRC tells your employer to apply the new code from your next pay date.9GOV.UK. Understanding Your Employees’ Tax Codes
If you overpaid tax under the old code, your employer’s payroll fixes it automatically. PAYE is cumulative, so the software recalculates your total tax liability for the year to date under the new code and hands back the difference. In practice, that usually shows up as a noticeably bigger take-home figure on your next payslip. You don’t need to submit a separate claim for the current tax year.
Getting Back Tax From Earlier Years
If a wrong code has been running for months or years, the in-year payroll fix only covers the current tax year. After 5 April each year, HMRC reviews PAYE records and may send a tax calculation letter called a P800, which sets out any overpayment or underpayment.10GOV.UK. Tax Overpayments and Underpayments
If the P800 shows an overpayment, you can claim the refund online and it typically arrives within five working days. If you don’t claim online within 45 days, HMRC sends a cheque. If no P800 has arrived but you think you overpaid for an earlier year, you can contact HMRC and ask for a review. Claims can generally go back four tax years.
If the P800 shows you underpaid, HMRC usually collects the amount by adjusting your tax code for the following year and spreading it across your monthly pay. Larger sums may be arranged separately.
Check Your Code Each Year Before April
HMRC typically issues new codes in January or February for the tax year starting on 6 April. That’s the moment to log in to your Personal Tax Account, look at the breakdown, and flag anything that doesn’t match your circumstances: a company benefit reduction that shouldn’t be there anymore, or a previous-year underpayment that’s already been cleared. Catch it before April and your first payslip of the new tax year comes through correctly, with no mid-year adjustment needed.