How much capital gains tax do I pay in the UK?

For disposals of shares, funds, and ETFs in 2026/27, taxable gains are generally charged at 18% to the extent they fall within the unused basic-rate band and 24% above it. The individual annual exempt amount is £3,000.

What is the capital gains tax allowance for 2026/27?

The individual annual exempt amount for the 2026/27 tax year is £3,000. It was £6,000 in 2023/24 and £12,300 in 2022/23.

How does the 30-day bed and breakfast rule work?

If you sell shares and repurchase shares of the same type within 30 days, the sale is matched with the subsequent purchase for CGT purposes. This anti-avoidance rule prevents investors from selling to realise a loss and immediately rebuying. FiscalFox applies this rule automatically.

Do I need to file SA108 for capital gains?

If you are registered for Self Assessment, you generally need to report gains when taxable gains exceed the annual exempt amount, when total disposal proceeds exceed £50,000 for 2023/24 onwards, or when you need to claim allowable losses or make another capital gains claim.

What does FiscalFox calculate for UK shares?

FiscalFox is a specialist UK capital gains tax calculator for share investors. It applies same-day matching, the 30-day bed and breakfast rule, and Section 104 pooling, then generates SA108-ready supporting reports. It has 13 built-in imports: Vanguard, Hargreaves Lansdown, Freetrade, Trading 212, eToro, InvestEngine, Moneybox, Saxo Bank, Interactive Brokers, Robinhood, Revolut, AJ Bell, and IG.

How do I report share sales to HMRC?

Share sales are reported on the SA108 supplementary pages of your Self Assessment tax return. You need to calculate the gain or loss on each disposal using HMRC's share matching rules, then enter the totals on SA108. The deadline is 31 January following the end of the tax year. FiscalFox can generate the SA108 schedules automatically from your broker export files.

Do I need to pay capital gains tax if my gains are under GBP 3,000?

If your total taxable gains are under the annual exempt amount, you do not owe CGT on those gains. If you are registered for Self Assessment, you may still need to report when total disposal proceeds exceed GBP 50,000 for 2023/24 onwards, or to claim allowable losses.

How do I calculate capital gains on shares?

Capital gains on shares are calculated as disposal proceeds minus allowable costs. HMRC requires same-day matching first, then acquisitions in the following 30 days, then Section 104 pooling. FiscalFox automates imported transaction matching and the current-year estimate. A brought-forward capital-loss balance must currently be applied separately.

What is the Section 104 pooling rule?

The Section 104 pool is a running average cost calculation for shares of the same type. When you buy shares, the cost is added to the pool. When you sell shares not matched by the same-day or 30-day rules, the cost is calculated as a proportion of the total pool cost based on the number of shares sold.

What are the current UK CGT rates?

From 30 October 2024: 18% for basic rate taxpayers and 24% for higher/additional rate taxpayers on shares and other assets. Before 30 October 2024: 10% and 20% respectively. Residential property has different rates.

What is the same-day rule for capital gains?

The same-day rule requires that if you sell shares and buy shares of the same type on the same day, the sale is matched with the same-day purchase for CGT purposes, regardless of the order of transactions during the day.

Can I carry forward capital losses?

Yes. If your capital losses exceed your capital gains in a tax year, you can carry forward the excess losses to offset against future capital gains indefinitely. You must report the losses to HMRC within 4 years of the end of the tax year in which they arose.

Is it really free to start?

Yes. Capital gains calculations are completely free, including calculations across multiple broker files. The one-time £29.99 payment is only needed to download the HMRC report pack, and unlocks the selected tax year plus earlier years in the calculation. There is no subscription.

Do you support my broker?

FiscalFox has 13 built-in broker imports: Vanguard, Hargreaves Lansdown, Freetrade, Trading 212, eToro, InvestEngine, Moneybox, Saxo Bank, Interactive Brokers, Robinhood, Revolut, AJ Bell, and IG. Other supported transaction files can use the opt-in AI import path after sign-in and consent.

Does FiscalFox apply HMRC share matching rules and protect data?

FiscalFox applies same-day, following-30-day and Section 104 matching in HMRC's prescribed order. Built-in broker parsing runs in the browser where possible; signed-in storage and opt-in AI parsing are described in the privacy policy. FiscalFox is a calculation tool, not tax advice or an HMRC submission.

When did CGT rates change in the UK?

The most recent change was on 30 October 2024, when the Autumn Budget increased CGT rates on shares from 10%/20% to 18%/24%. The annual exempt amount was reduced from £12,300 to £6,000 in April 2023, and further reduced to £3,000 in April 2024.

How do I know FiscalFox's calculations are correct?

FiscalFox applies the exact same share-matching rules HMRC uses to verify Self Assessment returns: same-day matching, 30-day bed and breakfast rules, and Section 104 pooling, in the correct priority order. Every disposal is traced and the calculations are defensible if you are ever questioned.

When do I need to pay for the report pack?

The free tier lets you calculate and view your capital gains on-screen. Pay £29.99 only when you want the downloadable HMRC-ready PDF and CSV report pack. The payment unlocks the selected tax year and every earlier year contained in the calculation.

Is there a subscription?

No. The report pack is a one-time £29.99 payment with no recurring charge. You can download the unlocked reports again whenever you need them.

What happens if my capital gains are wrong on my tax return?

If HMRC finds an error in your Self Assessment, you pay the extra tax plus interest, and a careless mistake can carry a penalty of up to 30% of the underpaid tax. Most DIY errors come from missing the same-day and 30-day matching rules. FiscalFox applies them automatically and keeps the workings behind every disposal so you can evidence your figures.

FiscalFox UK CGT Calculation Methodology and Validation

FiscalFox is an evidence-first calculator. It normalises supported broker records, resolves security identity, applies HMRC’s share identification order, and keeps disposal-level matches visible. Warnings are part of the result: they identify facts that software should not silently invent.

1. Source data and normalisation

Each supported importer maps the broker’s dates, transaction type, quantity, price, fees, currency and instrument identifiers into a common transaction model. File rows that cannot be interpreted safely are rejected or shown for review. An optional AI-assisted parser is only used after consent when a layout is not recognised.

2. Security identity across accounts

UK matching applies to the same shares held by the same beneficial owner, not to each broker statement in isolation. FiscalFox uses available identifiers and a security-resolution step to bring matching instruments together. Ambiguous identifiers remain review items.

3. HMRC share identification order

Same day: a disposal is matched with acquisitions of the same shares made on that date.
Following 30 days: remaining shares are matched with acquisitions in the 30 days after disposal, in date order.
Section 104 holding: any remainder is matched against the pooled holding and its average allowable cost.

This order follows HMRC helpsheet HS284. Pool histories are built chronologically even when the user filters the report to one tax year.

4. Gain, loss and estimated tax

For each disposal, proceeds are reduced by allowable disposal costs and the matched allowable acquisition cost. Gains and losses found in the imported transactions are then summarised for the selected year. The individual annual exempt amount is £3,000 in 2026/27. Main rates for shares are 18% and 24%, depending on the amount of the basic-rate band left after income.

Known limit: a capital-loss balance brought forward from earlier years is not currently entered or automatically applied. It must be considered separately in the final return.

5. Corporate actions and incomplete history

Potential splits, reorganisations, unmatched sales, duplicate rows and missing acquisition history can materially change a pool. FiscalFox detects or flags these conditions where possible. A warning is not a tax conclusion: the user or adviser must confirm the legal and economic facts of the event.

6. Validation and reproducible evidence

Automated tests cover core matching and tax logic, while importer tests use representative broker layouts. The report layer exposes transaction counts, proceeds, costs, gains, losses and matched lots so totals can be reconciled. See the sample 2025/26 report and the public changelog.

7. Reporting boundary

FiscalFox can estimate 2026/27 transactions using enacted rates and allowances. HMRC has not yet published the 2026/27 SA108 form, so SA108 field mapping is limited to filing years for which the official form is available. Reports are supporting calculations, not an HMRC submission and not personal tax advice.

FiscalFox calculation methodology