When HMRC deal with tax returns, they use a ‘process now, check later’ approach. This means they usually accept what you put on your Self Assessment without checking it straight away. So if you make a mistake, HMRC might not spot it right away.
How can I change a mistake on my tax return?
If you have made a mistake on a tax return, you can change the return within 12 months of the date that it’s due (31 January or 31 October).
If you submitted your return online, you can change the information online and the return will be updated.
If you filed a paper return, you usually need to send a new return, clearly marked “amended return”.
If you filed the original return late, you have 12 months from the date it was filed to make any changes.
If the change means you need to pay more tax, interest will be due on the underpaid tax from the original due date. If the change means you need to pay less tax, HMRC will process a repayment on request.
HMRC have guidance on correcting a return.
Can I claim relief if I’ve overpaid?
If you think you’ve paid too much tax because of a mistake on your tax return, you might be able to claim ‘overpayment relief’.
There are strict conditions about this relief and it may not be available in all cases.
You can make the claim between one and four years after the 31 January filing deadline. After four years the figures become final and late claims are only accepted in very exceptional cases.
What if HMRC get my tax bill wrong?
HMRC will send you your tax calculation. This tells you how much tax they think you need to pay. If you think it’s wrong, contact HMRC and ask them to tell you how they worked out the tax you owe.
If this shows that there has been a mistake, you should object in writing and ask for a correction. There is no formal process to appeal about a calculation mistake, but if it HMRC don’t correct it within a reasonable period, you can make a complaint.
Find out more about contacting HMRC.
Are there penalties for mistakes on returns?
The penalties for mistakes on tax returns are based on the intention behind them. HMRC looks at why the mistakes were made, whether it was a straightforward error or the information was deliberately put in wrongly or left out.
The penalties range from 0% to 100% of the tax that’s been over- or underpaid.
The penalty ranges are:
|
Behaviour |
Penalty range |
|
Reasonable care |
no penalty |
|
Careless behaviour |
from 0% to 30% |
|
Deliberate misstatement |
from 20% to 70% |
|
Deliberate misstatement which is then concealed |
from 30% to 100% |
There is detailed technical guidance on these terms on the HMRC website.