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Capital Gains Tax applies when you dispose of an asset and make a taxable gain. It is not a tax on the full sale proceeds. It is a tax on the profit after allowable costs, reliefs, exemptions and losses have been considered.
That sounds simple. In real cases, it often is not.
For London taxpayers, Capital Gains Tax can arise on property, shares, crypto assets, business assets, overseas investments and gifts to family members. The difficulty is rarely the headline rule. The difficulty is working out the correct gain, the correct reporting route and the evidence needed if HMRC later asks questions.
A person may sell a flat in Islington, transfer shares to a family member, dispose of crypto through several wallets, or sell a business asset after years of trading. Each case needs a different approach.
Tax Accountant London provides Capital Gains Tax advice for property, shares, crypto and business disposals where the calculation, reporting deadline or relief claim needs careful review.
What Capital Gains Tax means in practice
GOV.UK explains that Capital Gains Tax is charged on the gain when you sell or dispose of an asset that has increased in value. You can read the official overview on what Capital Gains Tax applies to.
A disposal does not only mean a sale for cash. It can also include a gift, transfer, exchange, insurance payout or certain transactions where you no longer own the asset.
This is where taxpayers often get caught. They assume that no cash means no tax. That is not always right.
For example, if you gift a buy-to-let property to an adult child, the tax calculation may still use market value. The same issue can arise with shares, land or other assets transferred between connected people.
There are special rules for spouses and civil partners, but these rules also need care, especially during separation or divorce.
When you need to report a gain
You usually need to report a gain when your total taxable gains exceed the annual exempt amount, or when the reporting rules require disclosure.
For UK residential property, the rules are more urgent. If tax is due on a UK residential property disposal, you may need to report and pay within 60 days of completion using the Capital Gains Tax on UK property service. GOV.UK explains this under reporting and paying Capital Gains Tax on UK property.
This deadline is one of the most common areas where taxpayers make mistakes. Many people only think about tax when their Self Assessment return is due. By then, the 60-day deadline may already have passed.
In practice, the CGT review should start before completion. At the latest, it should start as soon as the property sale completes.
The gain is not the same as the sale price
A gain normally starts with sale proceeds, less the original cost and allowable costs.
However, the detail matters. Purchase price, legal fees, stamp duty, estate agent fees, enhancement costs and disposal costs may all affect the calculation. Some costs reduce the gain. Others do not.
Repairs, mortgage repayments and general running costs are not usually part of the CGT base cost. This is a common misunderstanding.
For example, a landlord may sell a flat for £650,000. The mortgage balance may be £300,000. That does not mean the gain is £350,000. The mortgage is a financing issue, not the tax cost of the asset.
The tax calculation looks at acquisition cost, disposal proceeds and allowable deductions. The cash left after repaying the mortgage is a different figure.
Property gains need particular care
Property gains can involve several reliefs and restrictions. Private Residence Relief may apply if the property was your main home for some or all of the ownership period. Letting history, absence periods, occupation evidence and final period relief can all affect the result.
In London, this often matters because many owners move between homes, retain an old flat, let it out, then sell years later. The property may have been a home once, but that does not always remove the CGT charge.
The strongest property CGT calculations are evidence-led. They use completion statements, purchase records, estate agent invoices, improvement invoices, mortgage details where relevant, tenancy records and occupation evidence.
If the figures are estimated, the file should explain why. HMRC may challenge unsupported claims, especially for large improvement costs.
TIP: Keep capital improvement invoices separately from repair expenses.
A strong CGT file can save tax and reduce stress if HMRC reviews the disposal later.
Shares, funds and investment portfolios
Capital Gains Tax on shares can look easy, but the matching rules can make it more complex.
If you buy and sell shares in the same company over time, you cannot always use a simple first-in, first-out method. Same-day rules, 30-day rules and pooled costs may apply.
Investment platforms can produce useful reports. However, platform reports are not always enough. They may not include transfers from other brokers, historic costs, corporate actions, foreign exchange, equalisation or offshore fund issues.
A London-based investor with several platforms may need to bring the data together before the return is prepared. Otherwise, gains may be overstated or understated.
This is especially important where there are foreign funds. Some offshore fund gains can be taxed differently if the fund did not have UK reporting status.
Crypto disposals and record problems
Crypto creates a different type of Capital Gains Tax risk. HMRC does not view crypto as tax-free gambling. Disposals can include sales, swaps, spending crypto, gifting crypto or exchanging one token for another.
The main problem is records. A taxpayer may have used several exchanges, wallets and DeFi platforms. The tax calculation then needs dates, values, fees, transfers, disposals and cost history.
Where records are incomplete, the position still needs to be reconstructed reasonably. Ignoring old wallets or missing exchanges can create problems later.
Crypto gains also need care where there is income. Staking, mining, rewards or airdrops may have Income Tax points before any later capital disposal.
The best approach is to review crypto before the tax return deadline, not during the final week of January.
Gifts and family transfers
Family transfers often feel informal. Tax law is not informal.
A parent may give shares to a child. Siblings may transfer inherited property between themselves. One family member may buy out another. A property may be moved into or out of joint names.
These transactions can trigger CGT even where no money changes hands. Market value rules may apply between connected persons.
There may be reliefs, but they depend on the asset and facts. Business assets may qualify for specific reliefs. Transfers between spouses or civil partners may have special treatment. Divorce and separation have their own timing and court order issues.
This is an area where advice before the transfer is much better than advice after it.
Business disposals and relief claims
Capital Gains Tax can also arise when a sole trader sells a business, a partner disposes of a partnership interest, or a shareholder sells shares in a trading company.
Business Asset Disposal Relief may reduce the rate where the conditions are met. However, the conditions need checking. They can involve the type of business, shareholding, voting rights, office or employment status, holding period and the nature of the company’s activities.
A relief claim should not be treated as a simple box-tick.
For example, cash sitting in a company, investment activity, property income or group structure issues can affect the position. If a business sale is being planned, CGT advice should come before heads of terms are signed.
Common Capital Gains Tax mistakes
The most common mistakes are not always dramatic. They are often practical.
Taxpayers miss the 60-day property reporting deadline. They use sale proceeds instead of gain. They deduct mortgage balances. They claim improvement costs without invoices. They forget old enhancement costs. They overlook losses. They ignore foreign exchange. They treat gifts as tax-free.
Another common mistake is assuming the solicitor deals with Capital Gains Tax. Solicitors handle the legal completion. They do not normally prepare the CGT return unless specifically engaged to do so.
The taxpayer remains responsible for the tax position.
When HMRC risk increases
HMRC risk increases when figures are large, records are weak or the facts are inconsistent.
For property, HMRC may compare reported gains with Land Registry data, previous tax returns and rental income records. For shares and crypto, HMRC may look at platform information, bank movements or disclosures from third parties.
If HMRC opens a check, the response should be careful and evidence-based. Tax Accountant London also supports taxpayers with HMRC tax investigation advice where a disposal, relief claim or undeclared gain is being reviewed.
A calm response usually works better than a rushed one. It is important to answer the question asked, but not guess beyond the evidence.
A practical example
A taxpayer bought a London flat in 2012 for £420,000. She lived in it for four years, then moved in with her spouse and let the flat. She sold it in 2026 for £760,000.
The gain cannot be worked out by simply taking £760,000 less £420,000. Legal fees, stamp duty, estate agent fees and allowable improvement costs may reduce the gain. Private Residence Relief may also apply for the period she lived there and any qualifying final period.
However, the rental period may still leave a taxable gain. A 60-day CGT return may be needed if tax is due.
This is a typical case where a rough calculation can be wrong by thousands of pounds.
Conclusion
Capital Gains Tax needs more than a quick subtraction. The correct answer depends on the asset, ownership history, reliefs, costs, losses, reporting route and evidence.
The safest approach is to review the position before disposal where possible. If the disposal has already happened, act quickly, especially for UK residential property.
Good advice can help you report the right gain, claim the right relief and avoid weak assumptions that may not stand up later.
This article is for general information only. It is not personal tax advice and should not be relied on for your own circumstances. Capital Gains Tax depends on the asset, ownership history, residence position, records, reliefs and the tax year involved.
For tailored support, contact Tax Accountant London for personalised Capital Gains Tax advice, disposal calculations, property reporting or a review of your own circumstances before filing.