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The SA108 form: how to use it to file your Capital Gains Tax

  • 2 min read
  • Last updated 28 Mar 2024

The SA108 form is a document you need to fill and submit to HMRC if you have to pay tax on your capital gains.

Use it when you’ve sold any of these for a profit:

  • Shares (except from an ISA – gains from those are always tax-free)
  • Property
  • Bitcoin and other cryptocurrencies or tokens and other crypto assets
  • Art, jewellery, and antiques
  • Stamps and collectables
  • Any other assets that increased in value before you sold them

You’ll also need to pay capital gains tax when you gift any of these (this is a common situation for parents giving children a flat or house as a gift).

All of these will get taxed at the same capital gains tax rate, except for property, which has its separate CGT rate.

Another thing that you need to know about CGT on property is that, starting from April 2020, you now have to calculate, declare, and pay CGT within 30 days.

This is called the Real Time Capital Gains Tax Service. It’s now mandatory for all property sales and optional for all other capital gains.

For example, if you sold shares for a profit, you can use either this service or Self Assessment. If you sold a buy to let for a profit, you have to use the real time service.

How do I use it?

You can find the SA108 form on this HMRC page:

  1. Select the year that you need the form for
  2. Download it
  3. Print it
  4. Fill it in
  5. Attach it to your SA100 (the main tax return form)
  6. Send it to HMRC

In any case, make sure you first download and read the “Capital gains summary notes” for that tax year – it’s on the same HMRC page.

That pdf will explain what each item from the SA108 form means.

Do I need to use it if I submit my Self Assessment tax return online?


You will only need to file the SA108 form if you decide to file your tax return in paper format.

Reasons why you should use the online version instead:

  • The deadline for using the paper tax return is October 31st – for online tax returns is 3 months later (January 31st)
  • If you made a mistake, it’s easier to correct
  • HMRC will receive it instantly

If you find the online tax return challenging to use, at TaxScouts we can file your tax return online for you.

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