HMRC letter codes · Self Assessment (SA)
SA108Capital gains summary pages
Last reviewed 14 October 2026 · How Tax Letters checks its facts
In short
GOV.UK says to use the SA108 supplementary pages when filing your SA100 Tax Return to record capital gains and losses.
“Use the SA108 supplementary pages when filing your SA100 Tax Return to record capital gains and losses.”
GOV.UK: Self Assessment: Capital gains summary (SA108) · checked 14 October 2026
Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about SA108. Each fact has its source and the day it was checked beside it.
What it asks
GOV.UK's tax return forms page says you might need to fill in more sections, known as 'supplementary pages', if you are telling HMRC about certain types of income. It lists the SA108 supplementary pages for capital gains.
“You might need to fill in more sections, known as ‘supplementary pages’, if you’re telling HMRC about these types of income: … capital gains - SA108 supplementary pages”
GOV.UK: Self Assessment tax return forms · checked 14 October 2026
How to send it or apply
GOV.UK's guidance on completing the tax return, which lists SA108: Capital Gains summary 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 … SA108: Capital Gains summary”
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 SA108.
“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: Capital gains summary (SA108) (checked 14 Oct 2026)
- GOV.UK: Self Assessment tax return forms (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)