What is SA108 form?

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The SA108 form is the Capital Gains Summary pages that form part of a UK Self Assessment tax return. You use these pages to tell HMRC about capital gains and capital losses that you made during the tax year. The SA108 pages are not a separate tax return. Instead, they are completed and submitted together with your main Self Assessment return when you need to report gains from selling or giving away certain assets.

Many people never need to complete SA108 because they have nothing to report. However, if you have sold property, shares, business assets or other investments that create a taxable gain, these pages allow you to provide HMRC with the information they need to calculate any Capital Gains Tax that may be due.

If you are already completing a Self Assessment return, it is also worth understanding whether you can do a Self Assessment tax return yourself before deciding whether you need professional help.

What Is Included on the SA108 Capital Gains Summary?

The SA108 Capital Gains Summary is used to report details of your capital gains and capital losses for the tax year.

Depending on your circumstances, you may need to include:

• Gains from selling residential property.
• Gains from selling shares or investments.
• Gains from selling business assets.
• Capital losses that you want to claim.
• Reliefs that reduce your taxable gain.
• Information about assets held jointly with someone else.

HMRC uses the information entered on the SA108 pages together with the rest of your Self Assessment return to work out whether any Capital Gains Tax is payable.

What Are the SA108 Notes?

The SA108 Notes are HMRC’s guidance that explains how to complete each section of the Capital Gains Summary.

The notes help you understand:

• Which assets need to be reported.
• Which gains may be exempt.
• How to calculate your gain.
• Which reliefs may apply.
• How to report capital losses.
• What figures should be entered into each box.

The notes are designed to help taxpayers complete the form correctly, but they cannot cover every situation. Capital Gains Tax rules can become complicated where multiple assets have been sold, shares have been acquired at different times, or special reliefs apply.

Who Needs to Complete SA108?

You may need to complete SA108 if, during the tax year, you:

• Sold a buy-to-let property.
• Sold shares outside an ISA.
• Sold business assets.
• Disposed of land.
• Gave away valuable assets that create a taxable gain.
• Need to claim allowable capital losses.

Not everyone who sells an asset will pay Capital Gains Tax because exemptions, reliefs and the annual rules may reduce or remove the tax liability. Whether you need to complete SA108 depends on your individual circumstances and HMRC’s reporting requirements for the tax year.

Do You Always Need to Complete SA108 After Selling a Property?

No. Selling a property does not automatically mean you have to complete the SA108 pages or submit a Self Assessment tax return.

For example, if you are employed under PAYE, have no other reason to complete a Self Assessment tax return, and you sell a UK residential property that gives rise to Capital Gains Tax, you may only need to submit a Capital Gains Tax on UK Property return and pay any tax due within the required deadline. In these circumstances, HMRC does not require you to register for Self Assessment simply because you sold the property.

However, if you already complete a Self Assessment tax return for another reason, such as because you are self-employed, receive rental income, or HMRC has issued you with a notice to file, you must also include the disposal on the SA108 Capital Gains Summary pages, even if you have already submitted a separate UK Property Capital Gains Tax return. The tax already paid through the property return is taken into account when your Self Assessment is processed.

This distinction is often misunderstood:

• Not in Self Assessment? Report the property disposal through the UK Property Capital Gains Tax service if required, and you generally do not need to file an SA108 or a Self Assessment return solely because of that disposal.
• Already in Self Assessment? Complete the SA108 pages as part of your tax return and include details of the disposal, even if you previously submitted a UK Property Capital Gains Tax return.

Does Everyone Completing Self Assessment Need SA108?

No. Most taxpayers completing a Self Assessment return do not need the SA108 pages.

For example, if your tax return only contains employment income, self-employment income, rental income or pension income, you would normally complete the relevant supplementary pages instead.

Only taxpayers who have capital gains or capital losses that need reporting should include the SA108 pages with their tax return.

If you are unsure whether another supplementary page is required, it can also help to understand when to register for Self Assessment and which sections apply to your circumstances.

How Do You Calculate Capital Gains for SA108?

Before completing SA108, you normally calculate your capital gain by comparing what you received for the asset with its allowable cost.

Depending on the asset, you may also need to take into account:

• Purchase costs.
• Selling costs.
• Improvement costs that qualify.
• Reliefs available.
• Capital losses from the same or previous years.

The final figure is then entered onto the SA108 pages where required.

Because Capital Gains Tax calculations can become complex, especially where several assets have been sold during the same tax year, it is important that the calculations are completed correctly before submitting the return.

Can You Submit SA108 Online?

Yes. SA108 can usually be submitted electronically as part of your Self Assessment tax return using compatible tax software.

Not every version of HMRC’s own online service supports every supplementary page or every type of Capital Gains Tax reporting, so many taxpayers and accountants use commercial tax software when submitting more complex returns.

What Happens If You Make a Mistake on SA108?

If incorrect figures are entered on the SA108 pages, your Capital Gains Tax calculation may also be wrong.

This could result in:

• Paying too much tax.
• Paying too little tax.
• HMRC asking questions.
• Interest on unpaid tax.
• Penalties where errors are not corrected.

Checking your calculations before submitting the return can help avoid unnecessary problems later.

Do You Need an Accountant to Complete SA108?

Simple capital gains can sometimes be straightforward, but many transactions involve detailed tax rules, reliefs and calculations that are easy to misunderstand.

If you have sold property, shares, business assets or multiple investments, getting professional advice can help ensure the figures reported to HMRC are accurate and that any available reliefs have been claimed correctly.

If you are unsure whether you need to complete the SA108 Capital Gains Summary, how to calculate your gain, or which reliefs may apply, contacting a qualified accountant before submitting your Self Assessment return can help you avoid costly mistakes.

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