Key facts
- Check your tax code through your HMRC Personal Tax Account at gov.uk.
- Your tax code also appears on your payslip and your annual P60.
- Common errors include wrong allowances, old benefits in kind, or incorrect employment records.
- If your code is wrong, HMRC can usually correct it within a few weeks of being notified.
- Overpaid tax is refunded through PAYE or by HMRC direct payment; underpaid tax is collected through an adjusted code.
Why You Should Check Your Tax Code
Your tax code directly determines how much Income Tax your employer deducts from your pay. If it is wrong — even by a small amount — you could overpay or underpay tax throughout the year. HMRC makes millions of tax code changes every year, and errors do happen.[1]
It is good practice to check your tax code at the start of each tax year (April), whenever you receive a coding notice (form P2), and whenever your circumstances change.
Where to Find Your Tax Code
| Source | Details |
|---|---|
| HMRC Personal Tax Account | The most comprehensive view — shows your code, its components, and estimated tax for the year. Visit gov.uk/check-income-tax-current-year |
| Your payslip | Shows the code currently being used by your employer |
| HMRC coding notice (P2) | Sent by post or available online when your code changes — includes a breakdown of how it was calculated |
| Your P60 | Shows the final tax code used at the end of the tax year |
| HMRC app | The HMRC app shows your tax code and allows you to report changes |
What to Check For
When reviewing your tax code, look for these common issues:[2]
Allowances (should increase your code number)
- Is the Personal Allowance correct (£12,570 unless income exceeds £100,000)?
- Is the Marriage Allowance included if you have claimed it?
- Is the Blind Person’s Allowance included if applicable?
Deductions (should reduce your code number)
- Are benefits in kind still accurate (company car, medical insurance, etc.)?
- Is an underpayment being collected from a previous year?
- Is untaxed income (State Pension, rental income, etc.) being collected through your code?
- Has a benefit in kind been removed but the code not updated?
Common scenario: You returned your company car in January but your new tax code (issued in April) still includes a deduction for the car. This reduces your tax code unnecessarily, causing you to overpay tax. Contact HMRC to have the car benefit removed.
How to Correct Your Tax Code
If you spot an error:[4]
- Log in to your Personal Tax Account — you can update some details directly, such as reporting a change in benefits
- Call HMRC on 0300 200 3300 (Income Tax enquiries) — explain the error and provide any supporting information
- Write to HMRC — if the issue is complex, writing may be more appropriate (use the address on your coding notice)
HMRC will review your code and, if it agrees the code is wrong, issue a corrected code to your employer. This usually takes 2–4 weeks.
Dealing with Over- and Underpayments
Overpayment (you paid too much)
- If corrected during the year, your employer refunds the overpayment through your wages (the cumulative PAYE system handles this automatically)
- If the year has ended, HMRC sends a P800 calculation and refunds the overpayment by cheque or bank transfer
Underpayment (you paid too little)
- If under £3,000, HMRC usually collects it by reducing the following year’s tax code
- If over £3,000, HMRC may ask you to pay directly through Self Assessment or a payment plan
- You can sometimes request to pay through your tax code even for amounts over £3,000 if you prefer[3]
Tip: Check your tax code every April when the new tax year starts. HMRC issues new codes in February/March, and this is the best time to spot and correct errors before they affect your pay for the entire year.
Frequently Asked Questions
How do I check my tax code online?
Log in to your HMRC Personal Tax Account at gov.uk/check-income-tax-current-year. You will need a Government Gateway account. The service shows your current tax code, what makes up the code (allowances and deductions), and an estimate of the tax you will pay for the year.
What if my code shows a benefit I no longer receive?
If your code includes a reduction for a benefit in kind (such as a company car) that you no longer have, contact HMRC to have it removed. HMRC will issue a new code with a higher number, and your employer will refund the overpaid tax through your next pay. You can report the change through your Personal Tax Account or by calling HMRC on 0300 200 3300.
Can my employer change my tax code?
No. Only HMRC can change your tax code. Your employer must use whatever code HMRC instructs them to use. If you believe your code is wrong, contact HMRC directly — do not ask your employer to change it.
What happens if I have been on the wrong code for a whole year?
HMRC will issue a P800 tax calculation after the end of the tax year if you have overpaid or underpaid. Overpayments are refunded, either by cheque or direct to your bank. Underpayments under £3,000 are usually collected by adjusting the following year’s tax code; larger amounts may need to be paid directly.
Further Reading
- How Tax Codes Work — understanding what the numbers and letters mean
- Common Tax Codes Explained — 1257L, BR, 0T, K codes, and more
- Emergency Tax Codes — temporary codes and how to resolve them
- P60 Explained — your annual tax summary, useful for checking year-end figures
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Sources
- Check your Income Tax for the current year — GOV.UK
- Tax codes — GOV.UK
- Tax overpayments and underpayments — GOV.UK
- Tell HMRC about a change to your personal details — GOV.UK