Do I need to file Self Assessment?

If self-employed (over £1,000), company director, income over £150k, or significant untaxed income.

What records do I need?

All income sources, expenses, bank statements, invoices, and receipts for 5 years.

What are payments on account?

Advance payments towards next year's tax bill - 50% due 31 Jan, 50% due 31 July.

What is the penalty for late filing?

£100 immediately, then £10/day after 3 months, then 5% of tax after 6 and 12 months.

Yes, from 6 April after the tax year ends. Filing early does not mean paying early.

General2026/27

What is Self Assessment? UK Definition 2026/27

Written by Waqas Sagar ACA, FCCA, FMAAT

•

Verified by ICAEW, ACCA & AAT

•Updated April 2026

Quick Answer

The system for reporting income and calculating tax owed to HMRC.

Definition of Self Assessment

Self Assessment is HMRC's system for collecting income tax from people whose tax isn't fully collected through PAYE. You must file if self-employed with income over £1,000, a company director, or with untaxed income over £2,500. The deadline is 31 January following the tax year.

Self Assessment — Key Facts for 2026/27

Online deadline	31 January
Paper deadline	31 October
Payment deadline	31 January
Second payment	31 July (if POA)

How Self Assessment Works — Example

Self Assessment timeline

1Tax year: 6 April 2025 - 5 April 2026
2File by: 31 January 2027
3Pay by: 31 January 2027
4First POA due: 31 January 2027
5Second POA due: 31 July 2027

How Self Assessment Affects Your Tax

Missing the Self Assessment deadline triggers automatic penalties starting at £100. Keeping good records throughout the year makes filing easier. Consider filing early to know what you owe and spread payments.

Official HMRC Guidance on Self Assessment

For official guidance, refer to HMRC's documentation. Tax rules can change, so always verify current rates and thresholds on gov.uk.

HMRC: Self Assessment

Frequently Asked Questions about Self Assessment

Related Tax Terms

Payments on Account

Advance Self Assessment payments equal to 50% of previous years tax bill.

Accuracy Note

This information is for guidance only and is based on 2026/27 tax year rates. Tax rules are complex and your circumstances may differ. For personal advice, consult a qualified accountant or tax adviser.