SA108 Form: Filing, Instructions & CGT Supplement

What Is the SA108 Form?

SA108 is a supplementary form that is used by UK taxpayers to report capital gains as part of their annual self-evaluation. You might need to include the SA108 form with your SA100 tax return if you have sold shares, assets, or other chargeable assets. HMRC uses this data to calculate how much capital profit tax you have paid, if any. This form is required for profits above tax-free allowances, currently £ 6,000. If you fail to deposit HMRC SA108, where necessary, you risk punishment and delay in tax processing.

When Should You Use SA108?

This includes the sale or disposal of valuable personal property, stocks, and real estate for investments. This covers the sale or disposal of assets like stock, real estate for investments, or priceless personal belongings. You must include the SA108 form with your SA100 if you wish to claim capital losses or if you have made gains that exceed the annual tax-free allowance. It provides HMRC with a thorough understanding of your profits, losses, and any benefits to which you may be entitled.

It is a supplemental portion of the primary SA100 tax return, and the SA108 form is not filed separately. People frequently have to file it if they sold a second property, got compensation payouts for investment goods, or moved assets inside a trust. Your tax return will remain accurate and comprehensive if you use SA108, which guarantees that HMRC receives a correct breakdown of taxable gains.

How to Download the SA108 PDF?

The HMRC website offers a direct download of the official SA108 PDF. It is easier to fill out digitally because it is accessible in a fillable format. Visit HMRC’s form library to obtain the accurate version.

• Look up “SA108 Capital Gains” online.
• Select the SA108 PDF file.
• Use Adobe Reader to save and finish it.

Always look for the year printed in the SA108 PDF’s upper right corner. It needs to correspond with the tax year for which you are submitting, like 2025. Avoid using versions that are out of date. The official SA108 download is best for manual filers, but the form SA108 may be pre-filled or integrated if you use tax software.

Can You File SA108 Online?

You can file the SA108 form online, but only when it is presented as part of the return by using HMRC-approved software or through a tax agent. The standard online portal of HMRC does not allow individuals to add supplementary forms like SA108 directly through their personal tax account. If you are reporting Capital Gain Tax (CGT) from assets such as shares, assets, or other investments, the SA108 should be included through compatible software such as Tax Calls, Freezants, or GoSimplex with your SA100 returns. 

SA108 filing online ensures rapid processing and automatic calculations, which reduces the risk of manual errors. You have to download the correct software, input all CGT-related data in the SA108 section, and file it with your full return. This method also allows you to track submission status and get confirmation from HMRC. If you are uncertain about which software supports the SA108 form, HMRC’s website maintains an up-to-date list of compatible programs.

What Are the Key SA108 Notes?

HMRC’s SA108 notes serve as instructions that walk you through each form box. These points clarify:

• Meanings of each section (e.g., shares, property, cryptoassets)
• How to figure out profits and losses
• How to apply the permitted deductions
• How to record disposals in businesses
• How to incorporate the given assets or shared ownership

The SA108 notes are directly available on HMRC’s forms page. To prevent mistakes, read them before filling out the form. For example, the SA108’s Box 4 requests profits prior to reliefs. The SA108 annotations make it clear that this refers to before annual losses or exemptions are subtracted.

The SA108 notes also include instructions on how to claim any deferred taxes from SEIS investments, including entrepreneurs’ relief and gift holdover relief. When handling complex entries, particularly those involving partial asset disposals or asset pooling, referring to the HMRC SA108 advice helps to prevent misunderstandings.

How Does SA108 Link to SA100?

The SA108 Form is a supplementary schedule for the main SA100 tax return used by individuals in the UK. While the SA100 includes general income sources such as employment, pension, and savings, it does not include detailed segments for capital gains. This is the place where SA108 comes. If you have sold assets such as shares, other assets, or other investments, then you have to use SA108 to report your profit or loss with your SA100 submission. Without SA108, your capital gains cannot be properly evaluated by HMRC. 

Both forms are presented simultaneously as part of your self-evaluation returns. The SA100 offers observation, while the SA108 gives specific details about each property, acquisition and disposal dates, and any acceptable cost or relief. HMRC reviews both forms to determine your complete tax liability for the year. To put it briefly, the SA108 adds capital benefits to the SA100, which is the principal return, to make this announcement.

How Does the SA108 Calculator Work?

The SA108 calculator is a tool designed to help UK taxpayers estimate their capital gains tax (CGT) while filing the SA108 form. This simplifies the process by calculating taxable benefits based on asset details, acquisition costs, disposal values, ​​and applicable relief.

How it works: Input asset details. Users enter information like purchase price, sale price, and ownership period. Apply exemption and relief—the calculator considers the relief of private habitat relief and relief of entrepreneurs and reduces taxable income. 

Calculate taxable benefits

After cutting the exemption, the implementation of the equipment determines the final CGT liability based on the rate. Produce summary – users get a breakdown of their taxable advantage, which helps them to complete the SA108 form correctly. 

Benefits and Accuracy:

•  CGT reduces errors in calculation.
•  Efficiency – Saves time compared to manual calculations. 
• Compliance – Ensures reporting by correcting HMRC.

 For official guidance on SA108 and CGT calculations, visit the HMRC website. Before entering these figures into the SA108 form, make sure they are correct using the SA108 calculator. It lessens uncertainty and mistakes. Always be certain that the software calculator has the most recent CGT rates and annual exemption criteria.

Conclusion

For individuals declaring capital gains, the SA108 is an essential part of the UK tax system. To declare complete financial activity, it works in tandem with the SA100. The SA108 form might be required whether you’re cashing out on cryptocurrency, selling shares, or selling a property.

Use the SA108 calculator, always consult the SA108 notes, and make sure your submissions meet HMRC’s requirements. The SA108 form can be downloaded as a PDF, submitted online, and, if relevant, should be included in your yearly tax return.

Penalties or an underpayment of taxes may result from failing to submit your HMRC SA108 when it is due. Verify your gains, compute the appropriate amounts, and correctly file your return using the appropriate SA108 form version.