Runs 6 April to 5 April. Example: 2025-26 ends 5 April 2026.
Self Assessment guide
Self Assessment deadline 31 January
UK Self Assessment online deadline is 31 January. Paper is 31 October. That includes each partner’s SA100 and the partnership SA800 — late filing penalties explained.
In short
If you file Self Assessment online, HMRC must have your SA100 by 31 January after the tax year ends (6 April to 5 April). Paper returns are due by 31 October. Partnerships have a separate SA800 return due on the same paper and online dates for ordinary partnerships of individuals — the nominated partner must file it, and a late SA800 usually means every partner pays a penalty. Partners need the partnership statement from the SA800 before they can finish their own SA104. Always confirm current dates and penalties on GOV.UK.
Key dates
Always confirm the current year on GOV.UK. These are the standard UK rules most filers use.
Due by midnight 31 January following the tax year — usually also when balancing tax is payable.
Due by 31 October. Most people should file online instead.
If you are on payments on account, January and July dates still apply — filing and paying are related but not identical jobs.
Late filing and what to do
Penalties escalate the longer a return stays outstanding. Rules can change — treat this as a plain-English summary, not advice.
HMRC typically charges £100 for missing the online deadline on an individual return, even if you have no tax to pay.
Daily and further fixed or percentage-based penalties can apply if the return stays outstanding for months. Check GOV.UK for the current scale.
Submitting the return stops filing penalties growing. You can still arrange payment with HMRC separately.
Gather figures in autumn, review in December, file in January. Use draft → review → approve → file in the desk.
Partnership SA800 — who files and why it comes first
A partnership does not pay Income Tax itself. The nominated partner sends the partnership tax return (SA800). Every partner still files their own SA100 with their share (usually SA104). Figures below follow HMRC’s published guidance — always re-check GOV.UK for your year.
GOV.UK: the nominated (representative) partner registers the partnership for Self Assessment and is responsible for sending the partnership tax return. The other partners register separately and each file their own individual Self Assessment return.
For partnerships of individuals, HMRC’s SA800 guidance uses the same pattern as personal Self Assessment: paper by 31 October following the tax year, online by 31 January. If a company is a partner, different filing clocks can apply — confirm on GOV.UK for that partnership.
GOV.UK tells the nominated partner to complete the partnership return as soon as possible so other partners can use the information on their personal returns. In practice, each partner’s SA104 share comes from the SA800 partnership statement — so leaving the SA800 late blocks every partner’s accurate SA100.
HMRC’s compliance handbook and SA850 notes: if the partnership return is late, each person who was a partner in the return period is charged — not a single partnership-only fine. Initial fixed penalty £100 each; after three months, £10 per day (up to 90 days); after six and twelve months, further £300 fixed penalties each. Confirm the current scale on GOV.UK.
Sources: GOV.UK “Register the partnership”, HMRC SA800 / SA850 notes, and HMRC Compliance Handbook CH62940 (partnership late-filing penalties). This page is software guidance, not tax advice.
In our product
How to meet the deadline in Self Assessment Software
Prepare early with no card. Pay only when that tax year is ready to submit — individuals or the partnership SA800 path.
- Start the return early Open the tax year and complete pages as figures arrive — drafting never uses a credit or individual filing fee.
- Partnership desk first when needed Run the SA800 pack (and statement) so partners can copy allocations onto each SA104 before the personal filing crunch.
- Preview tax before January Run the combined calculation and SA302-style estimate so surprises are not left to the last week.
- Approve and file Move status to approved, pay for the year (or apply a practice credit), and submit from the filing desk.
Handbook
Related guides
Partnership tax return, statement, SA801–SA804 and vs SA104.
The main individual Self Assessment return — including partners’ pages.
Step-by-step from register to HMRC submit.
£69 path for SA104 and the SA800 desk.
FAQs
Deadline — questions answered
When is the Self Assessment deadline?
Online Self Assessment is due by 31 January after the end of the tax year (6 April to 5 April). Paper returns are due by 31 October. Always confirm the current year on GOV.UK.
When is the partnership SA800 due?
For ordinary partnerships of individuals, HMRC’s SA800 guidance follows the same pattern as personal Self Assessment: paper by 31 October following the tax year, online by 31 January. Partnerships with a company member can have different clocks — check GOV.UK for that case.
Who files the partnership tax return?
The nominated (representative) partner is responsible for sending the partnership tax return (SA800) to HMRC. Every partner still files their own individual Self Assessment return. See GOV.UK “Register the partnership”.
Why must the SA800 be done before partners finish their SA104?
Each partner’s share on SA104 comes from the partnership statement on the SA800. GOV.UK says the nominated partner should complete the partnership return as soon as possible so other partners can use that information on their personal returns.
What is the late filing penalty for an SA800?
If the partnership return is late, HMRC charges each relevant partner — not one partnership-only fine. HMRC’s published scale starts with £100 each, then daily penalties after three months, then further £300 fixed amounts at six and twelve months. Confirm the current rules on GOV.UK (see Compliance Handbook CH62940 and the SA850 notes).
What is the penalty for late Self Assessment filing?
For an individual SA100, HMRC usually charges £100 for missing the online deadline. Further daily and other penalties can apply if the return stays outstanding. Always check GOV.UK for the current rules.
Do I still need to file if I owe no tax?
If you are in Self Assessment, you normally still need to file by the deadline. Late filing penalties can apply even when the tax bill is nil.
Is the payment deadline the same as the filing deadline?
For many people, balancing payment is also due by 31 January. Payments on account have their own January and July dates. Filing on time and paying on time are both important.
Can I prepare my return before 31 January without paying?
Yes. In Self Assessment Software you prepare free with no card. You pay when you file that tax year — from £39 for individuals, or one practice filing credit per client year.
Prepare free
Do not leave the return to the last evening
Start free now, complete SA100 or SA800 pages as you go, and file when the year is ready.