The short answer
You can correct a submitted MTD tax return in your software within 12 months of the 31 January deadline. In SimpleTaxFlow, open your tax return, choose Start amendment, then Calculate amendment. Check HMRC’s new figures, tick both declarations and choose Submit amendment. After the window closes, follow HMRC’s guidance to change your return.
Is this the right guide?
Use this guide when HMRC has already accepted your Making Tax Digital tax return and you find something wrong. That could be a missed expense, income you left out, or an allowance you forgot to claim.
If you have not submitted yet, you do not need an amendment. Fix the figures and calculate again, using the guide to submitting your tax return. If you spot a mistake during the tax year, correct the record and your next quarterly update includes it.
How long you have to amend an MTD tax return
HMRC says you can change a tax return within 12 months of the submission deadline. The deadline is 31 January after the tax year ends. You make the change in your Making Tax Digital software, the same way you submitted.
SimpleTaxFlow shows the last day you can amend in the banner on your tax return. After that, the banner says the window has closed and you follow HMRC’s guidance instead.
What an amendment does
An amendment replaces your earlier tax return. HMRC works out your figures again from what it holds when you calculate, so your bill can go up or down.
Making Tax Digital does not change how or when you pay. You cannot claim a tax refund in your tax return using Making Tax Digital. If you are due money back, ask for it through your HMRC online account.
What you need
- The correct figures and the records or receipts behind them.
- HMRC connected to SimpleTaxFlow.
- Your original tax return reference, which Submission history keeps for you.
1. Correct the figures first
Fix whatever was wrong in SimpleTaxFlow first. That could be your records, allowances, adjustments, losses or other income. If a business figure changed, choose Open year-end steps. Under Resend Q4 if changed, review that business’s final update and send the corrected figures. The amendment uses what HMRC holds when you calculate it.
Open Tax2. Open your tax return
Open Tax and choose More. Under Your tax tools, choose Tax return. You can also choose Open year-end steps, then Review your tax return. The banner shows Amendment window open until your deadline.
Open your tax return3. Start the amendment
If you see Start amendment, choose it. The panel changes to Amend your tax return. Submission history under More also offers Start amendment next to a submitted tax return.
Open your tax return4. Calculate the amendment
Choose Calculate amendment. HMRC works out your revised Total liability, Income tax, NIC2 and NIC4. HMRC calls this step intent to amend. The amendment replaces your earlier tax return, so check the figures carefully. If you change something after this, choose Re-calculate.
Open your tax return5. Confirm and submit the amendment
Read both declarations and tick each box. Choose Submit amendment. You see Amendment submitted with a reference. Keep it.
Open your tax return6. Check what you owe
A correction can change your bill. Check HMRC for the new amount and any payment date.
Pay Self Assessment7. If the window has closed
If the banner says Amendment window has closed, you cannot amend in SimpleTaxFlow. Read HMRC’s guidance on changing a return after the time limit.
Read HMRC’s guidanceA worked example
Taylor (fictional) lets a house and submitted the tax return in June. In September Taylor finds a £1,000 repair bill that was never recorded. Taylor adds it in Money, opens the year-end steps and resends the final update for the UK property business.
Taylor then opens the tax return, chooses Start amendment and Calculate amendment, checks HMRC’s revised figures, ticks both declarations and chooses Submit amendment.
- Rent for the year
- £20,000
- Expenses in the original tax return
- £4,000
- Profit in the original tax return
- £16,000
- Repair bill found later
- £1,000
- Expenses in the amendment
- £5,000
- Profit in the amendment
- £15,000
HMRC works out the revised tax. Taylor checks the HMRC online account for the new balance.
Common mistakes
- Calculating the amendment before correcting the figures, so HMRC recalculates the old numbers.
- Adding a correction twice, once in a record and again as an adjustment.
- Waiting until the 12-month window has closed.
- Expecting the amendment to pay or refund anything by itself.
How to check it worked
After you submit, the tax return shows Amendment submitted with an HMRC reference. Under More, Submission history lists the amendment next to the original. Choose Compare with previous to see what changed, and Open receipt or Download to keep a copy.
Then sign in to your HMRC online account to check the new balance and any payment date.
Before you move on
- The wrong figures were corrected before calculating
- HMRC’s revised calculation was checked
- Both declarations were read and ticked
- The amendment reference is kept
- £29.99 + VAT a year. Bookkeeping is free. Pay when you send to HMRC.
Frequently asked questions
How many times can I amend my tax return?
You can amend it as needed while the window is open. Each amendment replaces the one before.
Do I need to send my quarterly updates again?
Correct your figures in SimpleTaxFlow first. If a business figure was wrong, the year-end steps show what to send again before you calculate the amendment.
How long do I have to amend my MTD tax return?
HMRC lets you change a tax return within 12 months of the 31 January submission deadline. SimpleTaxFlow shows the last date in the banner on your tax return.
Can I claim a refund through my amended tax return?
No. You cannot claim a tax refund in your tax return using Making Tax Digital. If the amendment means you are owed money, ask for it through your HMRC online account.
Check the official rules
Tax rules can change and individual circumstances matter. Use HMRC’s current guidance to confirm the treatment that applies to you.
Put the guide into practice.
Open the relevant workspace and complete the next step with this guide available in another tab.
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