Tax & Finance · Polar Small Business Update
Self Assessment deadline 2027: key dates for sole traders
The first important date is closer than January. Here are the deadlines for registering, filing and paying for the 2025/26 tax year—and what to prepare now.
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If you need to complete Self Assessment for 2025/26 and have not filed before, tell HMRC by 5 October 2026. Paper returns are due by 31 October 2026. Online returns and the tax owed are normally due by 11:59pm on 31 January 2027. Earlier preparation gives you time to understand the bill and protect cash flow.
The Self Assessment dates
5 October 2026
Tell HMRC if you need to complete a return and have not sent one before, or did not need to send one for 2024/25.
31 October 2026
Deadline for HMRC to receive a paper tax return.
30 December 2026
Deadline to submit online if you want HMRC to consider collecting the bill through your tax code, where eligible.
31 January 2027
Deadline for the online return and payment of the tax owed.
If you make payments on account, the second payment date is normally 31 July.
What records should a sole trader gather?
- Sales invoices, till records and other business income for 6 April 2025 to 5 April 2026.
- Receipts and records for allowable business expenses.
- Bank statements and payment-provider reports used to reconcile the figures.
- Details of other taxable income that belongs on the return.
- Previous payments on account and any relevant HMRC correspondence.
Keep business and personal spending clearly separated. If a cost is partly personal, do not assume the entire amount is deductible.
Why September is a useful time to act
Submitting early does not normally mean paying immediately, but it can reveal the likely bill months before the January payment deadline. That creates time to correct missing records, ask questions and plan the cash rather than discovering the figure at the last minute.
A calm preparation plan
This week
Confirm whether you need to file and register if required. Create one list of missing records.
This month
Reconcile income and expenses, then estimate the likely tax bill.
Before filing
Review unusual expenses, other income and payments on account.
After filing
Save the submission record and schedule the payment before 31 January.
How Polar can help
The Polar view
The best Self Assessment routine is not a January rush. Keep clean monthly records, estimate the tax as the year develops and treat the payment date as a planned business commitment.
Official sources
This article is general information, not tax advice. Your filing obligations depend on your circumstances. Check HMRC guidance or speak to a qualified adviser if you are unsure.