I’ve made a mistake with my tax? What can I do?

Aargh, I've made a mistake with my tax!

We all make mistakes. We’re only human after all. But what should you if you realise there’s a mistake in a tax return you’ve already submitted to HMRC?

The main thing to remember is that once you realise your mistake, you are responsible for letting HMRC know about it. If HMRC review your tax and discover an error they may enforce a penalty. The highest penalties are given for deliberate concealed errors.

So if you spot an error, do the right thing and be honest about it. Even if it may cost you a bit more at the time, it could save you a lot in the long run. HMRC are much more understanding about errors you highlight or correct yourself than they are about the ones they find!

Self Assessment

If it’s your last self assessment return that’s the source of the problem, then you or your accountant can simply resubmit the return. The deadline for re-submitting a return is a year after the filing deadline. For example tax year 2016-17 is due to be filed by 31 January 18 so the deadline for re-filing is 31 January 19.

You can refile using the same method you used originally, whether via your HMRC online account, via tax software or with a paper form.

If you’ve missed the deadline then you’ll need to write to HMRC. You need to include information about the tax year that you are correcting, why you think you paid too little or too much tax and how much you think you under or overpaid.

If you are claiming a refund for overpaid tax there are additional details that are required. You have up to 4 years after the end of the tax year to claim for any overpayments.

Corporation Tax

Correcting errors on your company tax return is similar to correct the self assessment return. Again you have twelve months from the filing deadline of the return to resubmit and correct any mistakes. This will depend on your company year end date. If you have a year end of 30 June 16 then the tax return is due 31 March 17 and the deadline for re-filing amendments is 31 March 18.

You can make amendments using the same method you used originally, whether via your HMRC online account or via tax software. You can also write to HMRC.

If you discover a mistake after the deadline for amendments, you’ll still need to let HMRC know by writing to them and pay any extra tax due. If you’ve overpaid you may well be able to get the tax back but it’s not guaranteed outside the amendment deadline.


Unlike the self assessment return or corporation tax return, the VAT return can’t be refiled. If you discover an error after you’ve filed your return, you’ll have to wait until next quarter to make a correction.

Most errors are easy to correct. If it’s an accidental error, from an accounting period within the last 4 years, of net value of less than £10,000, then it’s fine to make an adjustment to your next VAT return.

If the error was deliberate, was made more than 4 years ago or is above the threshold then you must report it. You can use form VAT652 or send a letter to the VAT Error Correction Team .

In summary

Remember, everyone makes mistakes sometimes, just don’t keep it to yourself!

‘Fess up about mistakes as soon as you can and make your amendments. If an amendment isn’t possible or you are in doubt, write a letter to HMRC.