Submitting your Self Assessment tax return to HMRC often feels like a job finally ticked off the list — until that uncomfortable moment when you realise something isn’t quite right. Maybe you’ve missed a bit of income, entered the wrong figure, or claimed an expense you shouldn’t have. In most situations, HMRC allows you to amend your tax return even after it’s been submitted. There are a few important rules and time limits to follow, though. This guide walks you through it in clear, straightforward terms.
Can you amend a tax return after submission?
You can, and many people do. HMRC gives taxpayers the option to amend a Self Assessment tax return after submission if changes are needed. The system is designed to allow corrections, recognising that mistakes are sometimes unavoidable. Sorting it out yourself sooner rather than later is usually the best approach.
Whether you’ve forgotten to include income from freelance work, misentered figures, or simply want to claim a relief you missed, most corrections can be made within a set timeframe and using the normal Self Assessment process.
Time limits for amending your return
One of the most common questions we hear is: “How long do I have to amend a tax return after submission?”
Here’s how it works in the UK:
- In most cases, you get 12 months from the official filing deadline to make changes to your Self Assessment return.
- When you file online, that filing deadline is 31 January following the end of the tax year.
- For example, if your 2024/25 return was filed by 31 January 2026, you’d generally have until 31 January 2027 to make any changes.
- It makes no difference when you actually submitted it — early or last minute — the amendment window is always counted from the deadline.
How to amend a tax return online
Amending your return online is normally the simplest and quickest way to make the change. HMRC’s digital services are set up so you can log in and submit your revised figures directly.
To get started, follow the steps below
- Log in to your HMRC online account via the Government Gateway.
- Go to your Self Assessment section.
- Select the tax year you want to amend.
- Choose the option to “Amend tax return” for that year.
- Enter the corrected figures or new information.
- Submit the amended return and save a confirmation for your records.
Once submitted, HMRC will update your tax calculation automatically based on the new information.
Can you amend immediately after filing?
If you’ve just filed online, some software services have a short delay (for example, a few days) before you can make an online amendment. But generally, as soon as your return has been formally processed by HMRC, you’ll be able to amend it within the 12-month window.
Amending paper tax returns
If you filed on paper, you can still amend your return — but the process is slightly different:
- Download a blank SA100 tax return form from HMRC’s website or request one by post.
- Complete it with the correct figures.
- On every page that has changes, clearly write “Amended return”.
- Include your name and Unique Taxpayer Reference (UTR) on each page and post it to HMRC.
HMRC treats this as a new submission that replaces the original for the purposes of your amendment.
What happens after you amend
After you’ve amended your return:
- HMRC updates your tax calculation using the new information.
- If the change means there’s more tax to pay, you’ll need to pay the difference. Interest is usually added from the original deadline.
- If the amendment shows you’re owed a refund, HMRC will sort that out once everything has been processed.
- It’s sensible to keep a copy of the amended return and any confirmations, just to be on the safe side.
What if you miss the 12-month amendment deadline?
If it takes you more than a year to notice the problem, the usual amendment route won’t be available. But that doesn’t mean the conversation stops there.
Claiming overpayment relief
If an error has meant you paid more tax than you should have and you’re outside the amendment window, you may still be able to claim overpayment relief from HMRC. This involves making a formal request for your money back.
Contact HMRC
Where the error isn’t a simple one, or the figures are on the higher side, writing to HMRC and talking them through the situation can help point you in the right direction.
Why it matters to amend a return
Correcting errors isn’t just about getting the right bill. It also helps you:
- Avoid extra charges that could arise if HMRC discovers the omission before it’s corrected.
- Keep your records in good shape, which can make future tax years and any HMRC follow-ups much easier to deal with.
- Secure refunds you might otherwise miss.
Being proactive and transparent with HMRC usually works in your favour, rather than waiting for HMRC to spot the issue.
Do I need professional help to amend a return?
Many people handle straightforward corrections themselves. But when there are multiple income sources or reliefs to consider, an accountant can help make sure everything is correct.
Will amending trigger an HMRC enquiry?
Usually not. Correcting a mistake on your own initiative generally reflects better than HMRC having to point it out later.
Are there penalties for amending my own return?
There’s no penalty just for amending your return within the allowed timeframe. Penalties tend to be about how the original error happened, not the fact you corrected it. Acting quickly helps keep things straightforward.
Final thoughts
Spotting something wrong on your tax return can knock your confidence, but it’s a situation many people find themselves in. What matters is dealing with it rather than hoping it won’t be noticed. HMRC allows genuine mistakes to be corrected, and most are easy to fix if you act in time.
Whether you end up paying a bit more tax or receiving a refund, handling it early keeps things under control. And if you’re unsure about the next step, an accountant can usually clear things up far quicker than trying to work it out on your own.
