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

The SA108 form is a supplementary document you must fill and submit to HMRC as part of your tax return if you have tax to pay on your capital gains. This is done via post.

While you can file your tax return online, some people prefer to, or can only post it. This is how you would report your capital gains and pay tax to HMRC when filing your tax return via post.

How do I know when I need to use the SA108 form?

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/tokens/crypto assets
• Art, jewellery, and antiques
• Stamps and collectables
• Any other assets that have 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 a separate CGT rate.

How do I use the SA108 form?

Since you’re posting your tax return, you’ll need to physically attach it to the main form (SA100). Therefore, you must print 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 (your tax return)
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.

Can I report capital gains and pay tax online without a tax return?

Yes. Starting from April 2020, all UK tax residents who sell residential property for a profit (not including your main home, of course) have to use the Real Time Capital Gains Tax Service.

You must:

• Report and pay within 60 days of selling a property from 27 October 2021 onwards
• Report and pay within 30 days of selling a property

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.

It’s primarily an online service, but there is a way to report CGT via post using the same service, without having to file a tax return.

Do I need to use a SA108 if I submit my tax return online?

No, you won’t need to use the SA108 form if you file your Self Assessment online, because you’ll fill in this information on your tax return instead.

If you previously used HMRC’s Real Time Capital Gains Tax to report the sale of your property and you have to file a tax return as well for another reason, you’ll still need to report any capital gains and tax paid so that your HMRC record is up to date.

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

Why is filing online easier?

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

Or, if you can’t be bothered with the hassle at all, TaxScouts can sort and file your tax return online for you.