Self-Assessment deadline 2026: what you need to know

If you're self-employed, a landlord, or have income outside of PAYE, the Self-Assessment deadline is one date worth having firmly in your calendar. Here's what actually matters.

The key date

Online tax returns for a given tax year (6 April to 5 April) must be submitted by 31 January the following year, and any tax owed is due by the same date. If you'd rather file a paper return, that deadline is earlier — 31 October. Almost everyone files online these days, so 31 January is the date to remember.

What happens if you're late

Missing the deadline triggers an automatic penalty, even if you don't owe any tax. That penalty increases the longer the return stays outstanding, and interest is added to any unpaid tax on top. It's a genuinely easy penalty to avoid, which makes it a frustrating one to receive.

Why leaving it late causes more than a fine

• Rushed returns are more likely to miss legitimate expenses and reliefs
• You lose the chance to plan for your tax bill in advance
• If you also make "payments on account," a late return delays working out what you actually owe

Our advice

Start gathering your records well before January — bank statements, invoices, expense receipts, and details of any other income. The earlier your return is prepared, the more time there is to plan for the bill, and the less likely anything gets missed in a rush.