An incorrect tax code can lead to overpaying or underpaying tax. This can happen if you change jobs, your benefits in kind change, or HMRC hasn’t updated its records from previous years

If you're not sure whether or not you're paying the right tax, we'd recommend checking out our "how do I work out my tax?" article and our free take home pay calculator to work out how much income tax and NI you should be paying.

If you'd like to understand more about how your own code is calculated, take a look at our tax codes explained guide.

What steps do I take if my tax code is wrong?

If you think you are paying the wrong amount of tax, you should contact HMRC on 0300 200 3300. Have as much information to hand as possible to support your view that your tax code is wrong (such as your P11D and P45 from previous employers).

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How HMRC handles a tax code correction

If HMRC agrees that your tax code is wrong, here’s what typically happens:

1. They review your details

HMRC will check the information you provide against what they already know about your income, benefits, and allowances. So make sure you have documents like P45s, P60s, P11Ds, and recent payslips handy to support your request. 

2. They issue a new tax code

If the information you give HMRC results in a change, they will issue a new tax code and communicate it to your employer and/or pension provider. You’ll also get a new coding notice explaining the change. 

3. Your employer applies the new code

Your next payslip after HMRC’s update should show your new tax code and the adjusted tax deductions.

4. Overpaid tax gets refunded

If HMRC’s correction shows you’ve paid too much tax, the way it’s refunded depends on when the overpayment occurred. 

During the current tax year:

You can usually reclaim the overpaid tax through your future payslip. You may see a small ‘catch-up’ adjustment on your next payslip to make up earlier overpayments. In some cases, HMRC may issue the refund directly to you. 

From a previous tax year:

HMRC can’t adjust past payrolls, so any refund is sent directly, either by bank transfer, cheque, or via a P800 tax calculation (sometimes called a tax reconciliation statement).

Can my accountant contact HMRC for me about an incorrect tax code?

Unfortunately, no. While your accountant can help you gather evidence if your tax code is incorrect, HMRC won’t accept communication from them on this matter. You’ll need to contact HMRC directly to sort out your tax code.

Essential information you need to correct your tax code

You’ll need your National Insurance number and your company PAYE scheme reference. Once you've got the right tax code, you'll be able to use our tax calculators to confirm that you're paying the correct amount.