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Correcting mistakes within 12 months

If you make a mistake on your tax return you have normally got 12 months from 31 January after the end of the tax year to correct it. This is called an 'amendment'. For example, for the 2011-12 return you have until 31 January 2024 to make an amendment.

You can only amend your return after this date if you received your tax return late (after 31 October). In this case you must correct any mistakes within 12 months of the deadline for sending your return back.

If you sent your tax return on paper, you do not need to send in the whole tax return again. Just write to HMRC and attach the tax return pages that you want to change, clearly marked 'amendment'. You’ll find the address on your tax return, your tax calculation or your Self Assessment Statement.

If you sent your tax return online it's easier if you make the amendment online too.

• Log in to or register for Self Assessment Online Opens new window

Getting a refund

If you think a refund is due you’ll need to tell HMRC how you'd like to receive it.

For convenience you can have it deducted from any tax due on your next Self Assessment Statement if either:

• it's less than £10
• a tax payment is due shortly

Or you can ask for one of the following:

• a repayment direct to your bank or building society account - this is quick and secure
• a cheque, however this will take a little longer to reach you

Sometimes HMRC may ask you for more information - to make sure that the figures are correct - before making a repayment.

Paying additional tax

If you owe more tax as a result of the changes to your tax return, HMRC will tell you how much you need to pay and when and how to pay it.

Correcting mistakes after 12 months

If you want to tell HMRC about a mistake after 12 months, it's too late to amend your return. You have to write to HMRC and tell them about the mistake instead.

Getting a refund

In most cases, you'll get the tax you have overpaid back, as long as you claim it in time. You must make a claim within four years of the end of the tax year that you are claiming for. For example if you paid too much tax in the 2008-09 tax year, you must make a claim by 5 April 2013. If you don’t make a claim within the time limit you'll miss out on any repayment due.

You must make your claim in writing and it should include:

• the tax year it relates to
• why you think you have paid too much tax
• evidence of the tax that's been paid
• your signature
• how you would like to receive any repayment due

Sometimes HMRC may ask you for more information - to make sure that the figures are correct - before making a repayment.

For convenience you can have the repayment deducted from any tax due on your next Self Assessment Statement if either:

• it's less than £10
• a tax payment is due shortly

Or you can ask for one of the following:

• a repayment direct to your bank or building society account - this is quick and secure
• a cheque, however this will take a little longer to reach you

Paying additional tax

If you owe more tax as a result of a mistake you've made, you should provide as much detail as possible when you tell HMRC. HMRC will work out the amount due and ask you to make a payment. Depending on the circumstances, you may have to pay interest on the amount due.

Interest on late payment and repayments

If you pay tax late or receive a repayment late, HMRC will add on any interest that's due. The rates of interest vary - you can find the current rate using the link below.

• HMRC official rates of interest on repayments Opens new window

If you need more help

To get more help you can telephone or write to HMRC.

• Contact the Self Assessment Helpline Opens new window

• Telephone or write to HMRC Opens new window

If you do not complete a Self Assessment tax return but want to claim a tax refund, follow the link below to find out how.

• Tax refunds and reclaiming overpaid tax

More useful links

• Understanding your Self Assessment Statement

Useful contacts

• Self Assessment and your tax return