How to Complete Your Final Declaration in ThisQuarter
The year-end step by step: add your non-business income and reliefs, trigger and review HMRC's tax calculation, and submit the final declaration that replaces the SA100 — all in ThisQuarter.
The short answer
To complete a final declaration in ThisQuarter, select the client and open Final Declaration. Add all non-business income and reliefs (employment/PAYE, dividends, savings, pensions, Gift Aid, Marriage Allowance), then trigger HMRC's tax calculation, review it, and submit the final declaration. This replaces the old SA100 and is due by 31 January after the tax year — 31 January 2028 for 2026/27.
The final declaration is the year-end submission that replaces the SA100. It spans all the client's businesses plus their other income, so it lives in its own section. This guide walks through it in ThisQuarter.
Before you start
- All four quarterly updates for each business should be filed.
- Have the client's other-income paperwork ready: P60, P11D, dividend vouchers, interest statements, pension paperwork.
Step by step
- Open Final Declaration with the client selected (or use the Year-end card on Data Entry).
- Add non-business income and reliefs — employment/PAYE, dividends, savings, pensions, Gift Aid, Marriage Allowance.
- Trigger HMRC's calculation — signal intent to finalise; ThisQuarter retrieves HMRC's figures.
- Review the calculation — the tax due, payments on account, adjustments.
- Submit the final declaration and keep the receipt.
It's a whole-person submission
Unlike quarterly updates (which are per business), the final declaration is a single client-level filing. Even with several income sources, there's just one final declaration that brings everything together for the year.
The crystallisation step
Finalising is a short, deliberate sequence:
- Intent to finalise — you tell HMRC you're ready.
- HMRC produces its calculation — ThisQuarter retrieves it.
- You review it — check every figure.
- You submit the final declaration — this locks the year in.
The review step matters: the final declaration is the legally significant filing, so confirm HMRC's calculation is right before you submit.
Deadline
The final declaration is due by 31 January following the tax year — 31 January 2028 for 2026/27, the same day your tax payment is due. Note that the first-year concession removing penalties for late quarterly updates does not cover the final declaration, so treat this as a hard deadline.
That's the year closed. For corrections to a quarter before you finalise, see the guide on reviewing and amending a quarterly update.
Step by step
- 1
Finish your quarterly updates first
Make sure all four quarterly updates for each business are filed. The final declaration builds on your year-to-date figures, so they need to be in and correct.
- 2
Open Final Declaration
Select the client and open the Final Declaration section (also reachable from the Year-end card on Data Entry). It's a client-level submission spanning all businesses plus other income.
- 3
Add non-business income and reliefs
Add anything that isn't self-employment or property: employment/PAYE (with P60 pay/tax and P11D benefits), dividends (UK and foreign), savings interest, pension contributions, Gift Aid and Marriage Allowance.
- 4
Trigger and review HMRC's calculation
Tell HMRC you intend to finalise. ThisQuarter triggers the tax calculation and retrieves HMRC's figures. Review the calculation carefully — the tax due, payments on account, and any adjustments.
- 5
Submit the final declaration
When you're satisfied the calculation is correct, submit the final declaration. This is the legally significant year-end filing that replaces the SA100. Keep the stored receipt.
Frequently asked questions
What is the final declaration?
It's the year-end submission that finalises your tax for the year and replaces the old SA100 Self Assessment return. It's a client-level filing that pulls together all your businesses plus your other income and reliefs.
What income do I add that wasn't in my quarterly updates?
Everything that isn't self-employment or property: employment/PAYE income and benefits, UK and foreign dividends, savings interest, pensions, Gift Aid and Marriage Allowance. Quarterly updates only cover your business income sources.
What is crystallisation?
It's the technical sequence at year-end: you signal intent to finalise, HMRC produces its tax calculation, you review it, and then you submit the final declaration to lock the year in. ThisQuarter walks you through each step.
When is the final declaration due?
By 31 January following the end of the tax year — the same deadline as the old Self Assessment. For 2026/27 that's 31 January 2028, and your tax payment is due the same day. The first-year penalty concession for quarterly updates does not cover the final declaration.
Can I change the final declaration after submitting?
The final declaration finalises the year, so treat it as definitive. Review HMRC's calculation carefully before you submit. If something is wrong, speak to HMRC about the correct route to amend a finalised year.
Related reading
How to Review and Amend a Submitted Quarterly Update
How to correct a quarterly update you've already filed in ThisQuarter — unlocking the period, amending the cumulative figures, resubmitting to HMRC, or cancelling to restore the filed version.
How to Add a Client and Send an HMRC Authorisation Request
For accountants: how to add a client in ThisQuarter, pass HMRC's proof-of-knowledge check, and send an authorisation request so you can file for them under your Agent Services Account.
How to Import Your Figures from a Spreadsheet into ThisQuarter
Bring your income and expenses into ThisQuarter from Excel or CSV — how the labelled import works, how to check the preview before applying it, and how it feeds straight into your quarterly update.