Wrong tax code? Here's how to fix it.
An incorrect tax code is the single most common reason UK workers overpay income tax. Find out if yours is wrong, how much it's costing you, and exactly what to do next.
Where to find your tax code.
Your tax code appears in several places. Check all of these to make sure they are consistent:
Your payslip
Usually in the top section under 'Tax Code' or 'PAYE Reference'
HMRC P2 notice
HMRC sends a 'Notice of Coding' letter when your code changes β check your post
Your P60
End-of-year summary document β issued by your employer by 31 May each year
HMRC Personal Tax Account
gov.uk/personal-tax-account β Check your Income Tax β Tax code
Signs your tax code is wrong.
β Your code is BR, 0T, or D0 on your main job
You're paying 20-40% tax with no personal allowance β overpaying by up to Β£2,514/year
β Your code shows a K prefix
A debt or benefit is being collected through your tax code β this may or may not be correct
β Your personal allowance seems too low (e.g. 900L instead of 1257L)
A benefit-in-kind or debt may have been incorrectly added to your code
β Your code ends in W1 or M1 (e.g. 1257L W1)
You're on a non-cumulative emergency basis β tax isn't being calculated cumulatively over the year
β You recently changed jobs but HMRC didn't update your employer
Your new employer may be using an old or incorrect code
How to get your tax code corrected.
Contact HMRC directly (fastest for simple cases)
Call HMRC Income Tax on 0300 200 3300 (MondayβFriday 8amβ6pm). Tell them your National Insurance number, your tax code, and why you think it's wrong. They can issue an updated code to your employer immediately. Your employer's payroll will apply it within 1β2 pay periods.
Update via your HMRC Personal Tax Account (online)
Log in at gov.uk/personal-tax-account and go to 'Check your Income Tax'. Select 'Tell HMRC about a change' to update your employment or income information. HMRC will recalculate and issue a new code to your employer automatically.
Ask your employer to contact HMRC
If the issue started when you joined your employer (e.g. they lost your P45 or used a default code), ask your payroll or HR team to contact HMRC using their PAYE reference. Employers have direct access to HMRC PAYE Online.
Submit a Self Assessment return
If you're required to file a Self Assessment return, the correct amount of tax will be calculated and any overpayment refunded automatically when HMRC processes your return.
What happens to the tax you already overpaid?
Once HMRC corrects your tax code, your employer will apply it going forward. Any tax overpaid in the same tax yearis automatically refunded through your payroll β you'll see a larger net pay in the next period as the cumulative calculation corrects itself.
For tax overpaid in previous tax years, you need to claim separately. HMRC will not automatically send you a refund β you must request it. See our full guide on how to claim a tax refund.
You can claim up to 4 tax years back. If you've been on the wrong code for years, this could be a significant refund. The average reclaim through a specialist service is over Β£1,600.
Check your full take-home pay
Make sure your monthly budget adds up. Use our comprehensive payslip calculator to see exactly how much you will take home after tax, pension, and student loan deductions.