Form detail
HMRC Form SA100
Self Assessment Tax Return
Country
United Kingdom
Revision year
2024
Methods
paper, efile
Updated
2026-05-20
Self Assessment Tax Return
Annual Self Assessment tax return for UK individuals with income outside PAYE.
Who must file: UK residents with self-employment income above 1,000 GBP, untaxed income, capital gains above the annual exempt amount, or HMRC notice to file.
Practical overview
SA100 is the core UK Self Assessment return. The deadlines are 31 October for paper filings and 31 January for online filings, with the same payment deadline of 31 January. The 'payments on account' regime requires 50 percent of prior-year liability each on 31 January and 31 July, which catches many newly-self-employed filers off guard.
Practical steps
- Determine whether you are required to file based on income types and HMRC notice.
- Register for Self Assessment by 5 October if it is your first return.
- Gather records: bank interest, dividends, rental income, self-employment accounts.
- File online via HMRC by 31 January (or paper by 31 October).
- Pay any balance and payments on account by 31 January.
Due-date notes
31 October paper / 31 January online; 31 January for balancing payment and first payment on account.
Timing: 31 January
Penalty snapshot
100 GBP automatic penalty after 31 January, plus daily penalties of 10 GBP from 3 months late up to 900 GBP, plus 5 percent of tax due at 6 months and 12 months late.
Related citations
Computed from the cross-reference graph. Links open the related entity on this site.
This entry cites
- FormHMRC Self Assessment
- FormHMRC SA800
Cited by
- FormHMRC SA800
- FormHMRC SA105
- FormHMRC SA106
Primary sources
- HMRC: Self Assessment tax returnsVerified 2026-05-20
- HMRC: SA100 publicationVerified 2026-05-20
Important disclaimer
This library is for general tax education only. Always verify filing obligations, due dates, and tax consequences against the cited primary source or with a qualified tax professional.