HMRC letter codes · Self Assessment (SA)
SA101Additional information pages
Last reviewed 14 October 2026 · How Tax Letters checks its facts
In short
GOV.UK says the SA101 supplementary pages are used when filing the SA100 Tax Return to record less common types of income, deductions and tax reliefs, and to provide information about Income Tax losses, pension charges and tax avoidance schemes.
“Use the SA101 supplementary pages when filing your SA100 Tax Return to record less common types of income, deductions and tax reliefs, and provide information about Income Tax losses, pension charges and tax avoidance schemes.”
GOV.UK: Self Assessment: additional information (SA101) · checked 14 October 2026
Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about SA101. Each fact has its source and the day it was checked beside it.
What it asks
GOV.UK's guidance on completing the tax return says you may need to send additional forms, known as supplementary pages, along with your SA100 tax return. It lists SA101: Additional information among the supplementary forms, for less common types of income, deductions and tax reliefs.
“You may need to fill in and send additional forms, known as supplementary pages, along with your SA100 tax return. … There are also supplementary forms if you need to record: … less common types of income, deductions and tax reliefs … SA101: Additional information”
GOV.UK: Complete your Self Assessment tax return for the last tax year · checked 14 October 2026
How to send it or apply
GOV.UK's guidance on completing the tax return, which lists SA101: Additional information among its supplementary forms, says you can file your tax return online and do not have to complete it all at once.
“You can file your tax return online … you do not have to complete it all at once … SA101: Additional information”
GOV.UK: Complete your Self Assessment tax return for the last tax year · checked 14 October 2026
Free help and HMRC contacts
For Self Assessment queries about returns, payments, replacements or notices, GOV.UK's general enquiries page gives the number 0300 200 3310 and links to information about call charges. The page does not name SA101.
“Call HMRC if you have a query about: … your Self Assessment returns, payments, replacements or notices … Telephone: 0300 200 3310 … Find out about call charges”
GOV.UK: Self Assessment: general enquiries · checked 14 October 2026
Free help first
These routes are described by GOV.UK, TaxAid and Citizens Advice themselves.
- HMRC's extra supportHMRC offers extra support if your health condition or personal circumstances make it difficult to contact HMRC, for example a mental health condition, financial hardship or being treated in hospital.
- Someone to deal with HMRC for youYou can authorise a friend, relative or voluntary organisation to talk to HMRC for you and help you fill in forms.
- TaxAidTaxAid helps people with tax problems who cannot pay for advice. Tax Help for Older People merged with TaxAid in July 2025.
- Citizens AdviceCitizens Advice gives confidential advice online, over the phone and in person, for free.
- GOV.UK: Self Assessment: additional information (SA101) (checked 14 Oct 2026)
- GOV.UK: Complete your Self Assessment tax return for the last tax year (checked 14 Oct 2026)
- GOV.UK: Self Assessment: general enquiries (checked 14 Oct 2026)
- GOV.UK: Get help from HMRC if you need extra support (checked 7 Oct 2026)
- GOV.UK: Appoint someone to deal with HMRC on your behalf (checked 7 Oct 2026)
- TaxAid: About us (checked 8 Oct 2026)
- Citizens Advice: About us (checked 7 Oct 2026)