Tax
Self-Assessment Deadline UK 2026: Key Dates
7 min read
Thistle Team•Tax & Compliance Experts
Key Deadlines 2025/26
- 5 Oct 2026: Register for Self-Assessment
- 31 Oct 2026: Paper return deadline
- 31 Jan 2027: Online return + payment deadline
- 31 Jul 2027: Second payment on account
Frequently Asked Questions
When is the Self-Assessment deadline?
31 October for paper returns, 31 January for online returns and payment.
What happens if I miss the deadline?
Automatic £100 penalty, plus daily penalties after 3 months and interest on unpaid tax.
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