Amending a submitted return

Mistakes can still be fixed after submission, but the route depends on when you spot the problem. After you submit your tax return, you normally have 12 months from the statutory filing date to make changes. For most people that date is 31 January after the tax year ends, although it can be later if HMRC issued your notice to file late.

How to amend within the normal window

Change the figures in software, request a fresh calculation, review the result, then confirm the amended return. HMRC's amendment flow uses the same income routes as the original return, followed by a new calculation and a further confirmation step. Amend as soon as you realise something is wrong rather than leaving it.

If the normal amendment window has passed

If it is more than 12 months after the normal deadline and you left out income, write to HMRC explaining the tax year, why you think you paid too little, how much was underpaid, and sign the letter. If you think you paid too much, you may be able to claim overpayment relief instead — normally up to 4 years after the end of the tax year. Overpayment relief must be signed by the taxpayer, not an agent.

If the mistake means more tax is due

Do not wait for HMRC to find it first. Telling HMRC voluntarily about errors may reduce potential penalties on outstanding tax.

If you need to change your return (GOV.UK)