Filing a Prior Year or Late Self Assessment Return

The Self Assessment dashboard defaults to the current tax year, showing a Start [year] return button for the most recently completed year. If you need to file for an earlier year — for example, a 2024-25 return that was due by 31 January 2026 — there is currently no dedicated button for this. You can access the form directly using a URL parameter.

Accessing a Prior Year Return

To open the Self Assessment form for a specific tax year, add `?tax_year=YYYY` to the Self Assessment URL, where `YYYY` is the year the tax year ended.

Tax year	URL parameter
2024-25 (ended 5 April 2025)	`?tax_year=2024`
2023-24 (ended 5 April 2024)	`?tax_year=2023`
2022-23 (ended 5 April 2023)	`?tax_year=2022`

Full URL example (2024-25):

``` https://tinytax.co.uk/self-assessment?tax_year=2024 ```

If you are filing for a specific director or individual (using their `person_id` from the directors tab), include that too:

``` https://tinytax.co.uk/self-assessment?person_id=XXXXX&tax_year=2024 ```

Opening the URL creates a new draft for that year if one does not already exist.

Late Filing and Penalties

HMRC charges automatic penalties for late Self Assessment returns:

• Day after deadline: £100 fixed penalty (even if no tax is owed or you get a refund)
• 3 months late: £10 per day for up to 90 days (max £900 on top)
• 6 months late: 5% of the tax due or £300 (whichever is greater)
• 12 months late: A further 5% or £300

The return must still be filed — penalties do not go away by not filing. TinyTax submits the return to HMRC and HMRC will calculate any penalty separately.

What Years Can Be Filed

TinyTax supports SA100 filing for any completed tax year within HMRC's filing window (generally going back several years). If a year is outside HMRC's acceptance window, the submission will be rejected with an HMRC error — contact HMRC directly in that case.

For a summary of what income types are covered, see What Our Self Assessment Filing Covers.