Self Assessment 2025/26: the key dates to put in your diary now

The Self Assessment calendar creeps up faster than most people expect, so here is a quick roundup of the dates that matter for the 2025/26 tax year:

• 5 October 2026: register for Self Assessment if you are filing for the first time. Miss this and you may not get your UTR in time for January.
• - 31 October 2026: deadline for paper tax returns.
• - 31 January 2027: online return deadline AND the date your tax bill is due — the balancing payment for 2025/26 plus your first payment on account for 2026/27.
• - 31 July 2027: your second payment on account is due.

Two things that catch people out every year:

1. The £100 automatic late-filing penalty applies even if you do not owe any tax. File on time regardless.
2. 2. Payments on account are each worth half of last year's tax bill — and you can skip them entirely if your bill was under £1,000.

Put the dates in your diary now and future-you will be grateful.