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31 January is non-negotiable: file and pay your Self Assessment on time
The UK tax year runs from 6 April to 5 April. If you’re self-employed or have untaxed income, you must submit and pay by 31 January. Below is your fully visual, easy-scan guide linked to the Stewart Accounting website.
Self Assessment deadline
File & pay the same day
Submitting without paying (or vice-versa) still triggers penalties and interest.
Understanding the Self Assessment timeline
Your earnings between 6 April and 5 April form one tax year. For 2023–24, file and pay by 31 January 2025. Unsure whether you must file? See who must send in a return.
Key Self Assessment deadlines at a glance (2023–24)
Bookmark this: your quick-reference guide.
| Task | Deadline | Notes |
|---|---|---|
| Tax year ends | 5 April 2024 | End of reporting period. |
| Register for Self Assessment | 5 October 2024 | Crucial for first-time filers. |
| Paper tax return | 31 October 2024 | Applies if filing on paper. |
| Online tax return | 31 January 2025 | Main deadline for most people. |
| Pay your tax bill | 31 January 2025 | Payment due same day as submission. |
| 2nd Payment on Account (if due) | 31 July 2025 | Typically 50% of previous year’s bill. |
Payments on Account (POA) — how they work
If your bill was over £1,000 and less than 80% collected via PAYE, HMRC usually requires two advance Payments on Account—on 31 January and 31 July—each about 50% of last year’s bill.
31 January
File, pay balance, and make first POA.
31 July
Second POA keeps January manageable.
Adjustments
If income falls, apply to reduce POA via Stewart Accounting.
Late filing penalties escalate fast
- After 31 Jan: £100 penalty (even if no tax due)
- 3 months late: £10/day for up to 90 days (max £900)
- 6 months late: +£300 or 5% of tax (whichever is higher)
- 12 months late: another £300 or 5%
- Interest: accrues from original due date
Watch: Self-employed deadline essentials (Quick Overview)
Why people miss the deadline (and how not to)
- Disorganisation: Receipts vanish. Fix: Use scanning apps weekly.
- Underestimating the work: It’s rarely a one-night job. Fix: Set a personal soft deadline early Jan.
- Life happens: Illness or family events. Fix: File early in December for breathing room.
A practical checklist for a timely return
- UTR (Unique Taxpayer Reference)
- National Insurance number
- All income records (invoices, bank, interest)
- Allowable expenses (travel, office, fees)
- Choose HMRC or software filing
- Double-check and keep PDF copy