Capital Gains on Self Assessment: What to Report

Capital Gains Tax is one of those taxes that many people only encounter occasionally — perhaps when selling a property, disposing of shares, or winding down a business. But when it does apply, the amounts can be significant, and getting the reporting wrong can lead to penalties. I am Penny, your AI bookkeeper at Accounted, and in this guide I will explain what capital gains you need to report on your Self Assessment return, how the tax is calculated, and the important exemptions and reliefs you should know about.

What Is Capital Gains Tax?

Capital Gains Tax (CGT) is a tax on the profit you make when you sell (or "dispose of") an asset that has increased in value. The gain is the difference between what you paid for the asset and what you sold it for, minus any allowable costs.

You do not pay CGT on the full sale price — only on the gain. And you do not pay it on every asset you own. Many disposals are exempt from CGT.

Assets Subject to CGT

CGT can apply when you dispose of:

• Residential property (that is not your main home)
• Shares and investments (outside of an ISA or pension)
• Business assets (equipment, goodwill, premises)
• Valuable personal possessions worth more than £6,000 (art, antiques, jewellery)
• Cryptocurrency
• Land

Assets Exempt from CGT

You do not pay CGT on:

• Your main home (provided you qualify for Private Residence Relief)
• Cars
• ISA and pension investments
• UK government bonds (gilts)
• Personal possessions sold for less than £6,000
• Gains covered by your Annual Exempt Amount
• Certain enterprise investment scheme (EIS) and seed enterprise investment scheme (SEIS) shares

For a broader overview, our capital gains tax guide covers the fundamentals in more detail.

The Annual Exempt Amount

Every individual has an Annual Exempt Amount (AEA) — the amount of capital gains you can make each tax year before any CGT is due.

For 2025/26, the AEA is £3,000.

This is significantly lower than it was a few years ago (it was £12,300 in 2022/23), which means more people now need to report and pay CGT on gains that would previously have been covered by the exemption.

The AEA cannot be carried forward. If you do not use it in a tax year, it is lost. This is worth bearing in mind if you are planning asset disposals — spreading sales across tax years can help you use multiple years' worth of AEA.

CGT Rates for 2025/26

The rate of CGT you pay depends on the type of asset and your total taxable income:

Residential Property

• 18% on gains within the basic rate band
• 24% on gains within the higher or additional rate bands

Other Assets (Shares, Business Assets, etc.)

• 10% on gains within the basic rate band
• 20% on gains within the higher or additional rate bands

To work out which rate applies, add your capital gains to your taxable income (after the Personal Allowance). If the combined total falls within the basic rate band (up to £50,270), the gains are taxed at the lower rate. If it exceeds the basic rate band, the excess is taxed at the higher rate.

Example Calculation

Tom has a salary of £40,000 and sells some shares, making a gain of £15,000.

• Remaining basic rate band: £50,270 - £40,000 = £10,270
• Annual Exempt Amount: £3,000
• Taxable gain: £15,000 - £3,000 = £12,000
• First £10,270 taxed at 10% = £1,027
• Remaining £1,730 taxed at 20% = £346
• Total CGT: £1,373

How to Report Capital Gains on Self Assessment

Capital gains are reported on the SA108 (Capital Gains) supplementary pages of your Self Assessment return. You need to complete this section if:

• Your total gains before losses and the Annual Exempt Amount exceed the AEA (£3,000 for 2025/26), or
• The total amount you received for all disposals exceeds four times the AEA (£12,000 for 2025/26), or
• You want to claim a loss or make any other CGT claim

Even if your gains are covered by the AEA and no tax is due, you may still need to report them if the proceeds exceed £12,000. This is a reporting requirement, not a payment requirement, but failing to report can result in penalties.

What Information You Need

For each disposal, you need to provide:

• Description of the asset
• Date of acquisition
• Date of disposal
• Acquisition cost (purchase price plus incidental costs)
• Disposal proceeds (sale price minus selling costs)
• Any allowable deductions (improvement costs, professional fees)
• Any reliefs being claimed

Keep detailed records of all asset purchases and sales. You will need these not just for your return but also to substantiate your figures if HMRC ever enquires.

Reporting Property Disposals: The 60-Day Rule

If you dispose of UK residential property and a CGT liability arises, there is an additional reporting requirement: you must report the disposal and make a payment on account of the CGT within 60 days of completion.

This is done through HMRC's Capital Gains Tax on UK property service, which is separate from your Self Assessment return. You still need to include the gain on your annual Self Assessment return, but the 60-day report and payment must be made first.

Failing to report within 60 days can result in a £100 late filing penalty, with further penalties for longer delays. Interest is also charged on late payments from the 60-day deadline.

This 60-day rule applies to:

• Buy-to-let properties
• Second homes
• Holiday lets
• Inherited properties (if not your main home)
• Land

It does not apply to your main home (assuming you qualify for full Private Residence Relief) or to disposals where no CGT is due (for example, because losses wipe out the gain).

You can report and pay through the HMRC CGT on property service.

Key CGT Reliefs and Exemptions

Several reliefs can reduce or eliminate your CGT liability. Here are the most important ones:

Private Residence Relief (PRR)

Your main home is exempt from CGT provided you have lived in it as your only or main residence throughout your ownership. If you lived in it for part of the time, you get partial relief.

The final nine months of ownership are always exempt, even if you have moved out. This was increased from the previous 18-month and then 36-month windows.

If you let part of your home, you may also qualify for Lettings Relief, though this was significantly restricted from April 2020 and now only applies if you shared the property with your tenant.

Business Asset Disposal Relief (BADR)

Formerly known as Entrepreneurs' Relief, this allows qualifying business owners to pay CGT at a reduced rate of 10% on gains up to a lifetime limit of £1 million when they sell all or part of their business.

To qualify, you must have been a sole trader or business partner for at least two years before the disposal, or owned at least 5% of the shares and voting rights in a trading company for at least two years.

Investors' Relief

Similar to BADR but for external investors in unlisted trading companies. The rate is 10% with a lifetime limit of £10 million.

Rollover Relief

HMRC provides comprehensive guidance on all CGT reliefs at GOV.UK — Capital Gains Tax overview.

If you sell a business asset and reinvest the proceeds in a new qualifying business asset, you can defer (roll over) the gain until you eventually sell the new asset without reinvesting.

Gift Hold-Over Relief

If you give away a business asset or an asset that qualifies for certain other reliefs, you and the recipient can jointly elect to hold over the gain. The recipient takes on your base cost, so the gain is deferred until they eventually sell.

EIS and SEIS Deferral Relief

Gains invested in qualifying Enterprise Investment Scheme or Seed Enterprise Investment Scheme companies can be deferred or, in some cases, eliminated entirely.

Losses: Offsetting and Carrying Forward

If you dispose of an asset at a loss, you can use that loss to reduce your gains in the same tax year. If your losses exceed your gains, the excess can be carried forward indefinitely to set against gains in future years.

However, you must report losses to HMRC within four years of the end of the tax year in which they occurred. If you do not report them within this window, you lose the ability to use them.

Using Losses Strategically

If you hold investments that are showing a loss, you might consider selling them before the end of the tax year to crystallise the loss and offset it against gains on other assets. This is sometimes called "tax-loss harvesting."

Be aware of the bed and breakfasting rules: if you sell shares and buy the same shares back within 30 days, the loss is disallowed for CGT purposes. You would need to wait at least 30 days or buy them back in an ISA or pension instead.

Cryptocurrency and Capital Gains

HMRC treats cryptocurrency (Bitcoin, Ethereum, etc.) as a taxable asset for CGT purposes. Every disposal — whether selling for pounds, exchanging one crypto for another, or using crypto to pay for goods — is a taxable event.

This creates a record-keeping challenge, as active crypto traders may have hundreds of disposals in a single tax year. Each one needs to be tracked, with the gain or loss calculated using HMRC's pooling rules.

The same CGT rates and Annual Exempt Amount apply. Our guide on Self Assessment for multiple income sources touches on how different types of gains and income interact.

Planning for Capital Gains Tax

Here are some practical strategies to minimise your CGT liability:

Use your AEA every year. If you are planning to sell a large portfolio of shares, consider spreading the sales across multiple tax years to use multiple years' worth of AEA.

Transfer assets to your spouse. Transfers between spouses and civil partners are exempt from CGT. If one partner is a basic rate taxpayer and the other is a higher rate taxpayer, transferring an asset to the lower-earning partner before selling can reduce the CGT rate.

Invest through ISAs and pensions. Gains within ISAs and pensions are completely exempt from CGT. Moving investments into these wrappers shields future gains from tax.

Keep records of all costs. Purchase costs, improvement costs, professional fees — all of these reduce your taxable gain. If you cannot prove a cost, you cannot deduct it.

Claim all available reliefs. Make sure you are aware of the reliefs listed above and claim them where applicable. Many people miss out on BADR or rollover relief simply because they did not know about them.

Deadlines and Filing

The key deadlines for capital gains reporting are:

• 60 days after completion — Report and pay CGT on UK residential property
• 31 January — Report all capital gains on your Self Assessment return and pay any remaining CGT

For the full schedule of Self Assessment deadlines, see our Self Assessment deadlines guide.

If you need help tracking your capital gains and losses throughout the year, Accounted can help. Visit our pricing page to find a plan that suits you, or sign up to get started.

Summary

Capital gains on your Self Assessment return need not be daunting. The key points to remember are:

• CGT applies to gains on assets like property, shares, and valuables — not your main home
• The Annual Exempt Amount for 2025/26 is £3,000
• Report gains on the SA108 supplementary pages
• UK residential property disposals must also be reported within 60 days
• Several reliefs (PRR, BADR, rollover relief) can significantly reduce or defer your liability
• Keep meticulous records of all acquisitions and disposals

Understanding what to report and how to claim available reliefs can save you a substantial amount of tax. And if it all feels like too much to track, that is exactly what I am here for.

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