How to Submit Your MTD Final Declaration to HMRC

You submit your MTD Final Declaration through your MTD-compatible software by 31 January following the end of the tax year, after adding any income HMRC hasn't already included and checking your tax calculation is correct. It replaces the traditional Self Assessment return for anyone within Making Tax Digital for Income Tax. If you've just finished your fourth quarterly update, the Final Declaration draws those updates together into one year-end submission that closes your tax year.  

This article covers the step-by-step process on how to submit your tax return, what HMRC adds automatically versus what you add yourself, what happens if you miss 31 January, and how filing differs if an accountant submits for you.

You must submit your MTD Final Declaration fro income tax by 31 January following the end of the relevant tax year. You can submit it earlier if you're ready, any time from 6 April in the new tax year onwards. For the 2025/26 tax year, that means you can file any time from 6 April 2026, with 31 January 2027 as the final deadline. 

Once your adjustments are done, you must use your MTD-compatible software to check that every other taxable income source and gain for the year is included before you submit. Any correction you make overwrites the previous entry. HMRC pre-populates some of this data automatically. Everything else is your responsibility to add, and skipping this step is one of the most common reasons a Final Declaration is filed inaccurately. 

You'll find whatever HMRC has added in your software when you request a calculation, or in your HMRC online services account. 

Once every income source and gain is added and checked, submitting the Final Declaration follows the same three-step process for every taxpayer, regardless of software provider: 

1. Confirm you're ready to submit. Go into your MTD-compatible software and indicate you're ready to move from quarterly updates to your Final Declaration. 
2. View and check the tax calculation. Your software will generate a calculation based on your quarterly updates and any income added. Review every figure before proceeding and rectify errors if any. 
3. Declare and submit. Submit your Final Declaration by declaring that the information is correct and complete to the best of your knowledge. Your software will confirm the submission with an on-screen message once it's gone through. 

This replaces the single "submit return" click that Self Assessment filers are used to. There is no separate portal. The Final Declaration is submitted entirely through your MTD-compatible software, not through HMRC's existing Self Assessment online service. 

Submitting your Final Declaration is what generates your Self Assessment tax bill for the year. The figure your software calculates becomes the amount HMRC expects you to pay. Payment itself works exactly as it always has. 

If You Use an Accountant to Submit MTD ITSA on Your Behalf 

If your accountant is your main agent for MTD ITSA, the submission process has two extra steps built in for your protection. Your accountant will confirm they're ready to submit and check the calculation, exactly as you would. But before anything is filed, they must share a copy of the information being submitted with you, and you must check it and give written confirmation that it's correct and complete. Only then can your accountant submit the declaration on your behalf. 

If a supporting agent rather than your main agent has sent your quarterly updates or added income sources, your main agent can view that information in their software but cannot access your underlying digital records directly. Any errors or missing information still need to be corrected before the Final Declaration goes in.

Missing the Final Declaration deadline puts you into the same points-based penalty system that applies to late quarterly updates. A late submission earns a penalty point; once you reach the relevant points MTD threshold, a £200 penalty applies, with a further £200 for each subsequent late submission.  Missing the payment deadline carries its own late payment penalty, separate from the late submission point above. For details on MTD penalties read our guide.  

Yes. You can amend a submitted MTD Final Declaration within 12 months of the submission deadline, using your MTD-compatible software rather than HMRC's older Self Assessment portal. Once you make a change, your HMRC online services account or your agent's agent services account, if they submitted on your behalf will show an updated tax calculation. 

If the error is actually in your underlying digital records rather than the declaration itself, correct your digital records first rather than amending the Final Declaration directly. The two are handled differently in your software.

Most errors in a first MTD ITSA Final Declaration aren't calculation errors. They're omissions. A landlord sees PAYE income already populated in their software and assumes the rest of their tax position is equally complete. Savings interest gets missed. A dividend from their own company gets missed. The gap surfaces later, when HMRC's records don't match what was filed, and by then the 12-month amendment window is running. Treating the Final Declaration as a reconciliation exercise, not a formality, is what separates a clean submission from one that needs correcting later. 

If you'd rather not carry that risk into your first Final Declaration, the safer route is to have an accountant or agent handle the submission on your behalf.