Do I Still File a Self Assessment Return if I Don’t Know My Profit Yet?

Key takeaways

• You still need to send a Self Assessment tax return even if you do not know your profit for the whole tax year.
• If you do not have final figures by the filing deadline, HMRC says you should use provisional figures and tell HMRC you’ve done so.
• Once you have the final numbers, you’ll need to change your return (you have 12 months from the Self Assessment deadline to make changes).
• If your final figures mean more tax is due, HMRC charges interest from the original due date; if you overpay, HMRC pays interest to you.

Do I still file if I don’t know my profit yet?

Yes. You still need to send a tax return even if you do not know your profit for the whole tax year. If you do not have final profit figures by the deadline, HMRC says you should submit the return using provisional figures and then update it later.

Why you might not know your full-year profit in time

HMRC recognises that, in some cases, you may not have final figures before the reporting deadline—for example, if:

• your accounting period ends at a different time to the end of the tax year
• your accounting period is different to your basis period
• you’re waiting for a valuation

What HMRC says to do (practical approach)

1) Work out provisional figures

If you do not know your profit for the whole tax year before the reporting deadline, HMRC says you should work out what it’s likely to be (your provisional figures) and include those in your return.

2) Tell HMRC you used provisional figures

HMRC says you should tell them you’ve used provisional figures when you submit your return.

The key is not to miss the filing deadline just because your accounts are not fully final.

3) Change your return when you have the final figures

When you find out your actual profit for the whole tax year, you’ll need to change your return. HMRC says you have 12 months from the Self Assessment deadline to make changes.

4) Be aware of interest if your estimate was low (or high)

HMRC says:

• if more tax is due, you’ll need to pay interest on the difference between your estimates and the final figures (worked out from the original due date for payment)
• if you overpaid, HMRC will pay interest to you

Deadlines to keep in mind (so you don’t miss filing)

HMRC’s deadlines depend on how you file:

What you’re doing	Deadline (as stated by HMRC)
Paper tax return must be received	11:59pm on 31 October 2025
Online tax return must be submitted	11:59pm on 31 January 2026
Pay what you owe	11:59pm on 31 January 2026
If paying through your tax code (where available)	11:59pm on 30 December 2025

Common mistakes to avoid

• Waiting for perfect numbers and missing the filing deadline (HMRC expects provisional figures if you genuinely do not know yet).
• Forgetting to flag that you used provisional figures when you submitted.
• Not updating the return once final figures are available.

Quick checklist

• File your return by the deadline (even if your profit isn’t final)
• Use provisional figures if needed
• Tell HMRC you used provisional figures when you submit
• Update (change) the return once you have final figures (within 12 months of the Self Assessment deadline)
• Budget for possible interest if your final tax bill increases

Summary

If your profit figures are not final by filing time, HMRC’s guidance is to file anyway using provisional figures, tell HMRC you’ve done that, and then change your return once you know the final numbers (within 12 months of the Self Assessment deadline).