Frequently Asked Questions

Capital gains tax (CGT) is a UK tax charged on the profit you make when you sell or dispose of an asset that has increased in value. For share investors, this means the difference between what you paid for your shares (including dealing costs such as broker fees and stamp duty) and what you received when you sold them. CGT is only charged on the gain itself, not on the total sale proceeds. It applies to shares, funds, ETFs, and other securities held outside of tax-sheltered accounts. The tax is calculated on a per-tax-year basis (6 April to 5 April) and reported to HMRC through Self Assessment.

You may need to pay CGT if you are a UK resident and you dispose of chargeable assets during the tax year. In the context of investing, a disposal includes selling shares, gifting shares (other than to a spouse or civil partner), and exchanging shares as part of a corporate action such as a takeover. You are liable if your total chargeable gains exceed the annual exempt amount after deducting any allowable losses. If your gains fall below the annual exempt amount, you may still need to report the disposals to HMRC if your total disposal proceeds exceed four times the annual exempt amount.

No. Shares held within a Stocks and Shares ISA, a Lifetime ISA, or a pension scheme such as a Self-Invested Personal Pension (SIPP) are completely exempt from capital gains tax. Any gains realised within these tax wrappers are not chargeable and do not need to be reported to HMRC. This exemption is one of the key advantages of using ISAs and pensions for investing. CGT only applies to investments held in general investment accounts (sometimes called dealing accounts or taxable accounts) that are outside of these tax-sheltered wrappers.

Capital gains on shares and investments are reported as part of your annual Self Assessment tax return. The deadline for filing online is 31 January following the end of the tax year. For example, for the 2024/25 tax year (which runs from 6 April 2024 to 5 April 2025), the online filing deadline is 31 January 2026. If you choose to file a paper return, the deadline is earlier: 31 October 2025. Any CGT owed must also be paid by 31 January. HMRC charges penalties for late filing and interest on late payments, so it is important to meet these deadlines.

Following the Autumn Budget 2024, the CGT rates on shares and financial investments changed on 30 October 2024. For disposals made on or after that date, the basic rate is 18% and the higher rate is 24%. Prior to 30 October 2024, the rates were 10% (basic rate) and 20% (higher rate). The rate you pay depends on your total taxable income: if your income plus gains fall within the basic rate band (up to £37,700 for 2024/25), you pay the basic rate. Gains that push you above this threshold are taxed at the higher rate. These rates apply to shares, funds, and ETFs, not to residential property, which has separate rates.

The annual exempt amount (also called the CGT allowance) for the 2024/25 tax year is £3,000. This is the amount of capital gains you can realise tax-free each year. The allowance was reduced significantly in recent years: it was £12,300 in 2022/23, fell to £6,000 in 2023/24, and dropped again to £3,000 for 2024/25 and 2025/26. The annual exempt amount cannot be carried forward; if you do not use it in a given tax year, it is lost. This reduction means that many more investors now face a CGT liability than in previous years.

There have been two major changes in recent years. First, the annual exempt amount was cut from £12,300 (2022/23) to £6,000 (2023/24) and then to £3,000 (2024/25 onwards). Second, the Autumn Budget 2024 increased the CGT rates on shares from 10%/20% to 18%/24%, effective from 30 October 2024. This means the 2024/25 tax year has split rates: the old 10%/20% rates apply to disposals before 30 October 2024, and the new 18%/24% rates apply from that date onwards. For the 2025/26 tax year, the 18%/24% rates apply for the entire year.

Your CGT rate depends on your total taxable income for the year. For the 2024/25 tax year, the personal allowance is £12,570 and the basic rate band is £37,700. If your taxable income (after deducting the personal allowance) is below £37,700, you are a basic rate taxpayer. Your capital gains are added on top of your income, so if your income plus gains exceed the basic rate threshold, the portion of gains above the threshold is taxed at the higher rate. For example, if you have taxable income of £35,000 and gains of £5,000, £2,700 of the gain falls within the basic rate band and £2,300 is taxed at the higher rate.

HMRC share matching rules determine which shares are treated as having been sold when you make a disposal. Since shares of the same class in the same company are interchangeable, HMRC requires you to follow a specific order to match sales with acquisitions. The three rules, applied in strict priority order, are: (1) the same-day rule, which matches sales with purchases made on the same day; (2) the 30-day bed and breakfast rule, which matches sales with purchases made within 30 days after the sale; and (3) the Section 104 pool, which uses a weighted average cost basis for all remaining shares. These rules are fundamental to correctly calculating capital gains tax on share disposals.

The same-day rule is the first of HMRC's share matching rules. If you sell shares and buy shares of the same class in the same company on the same day, the sale is matched with the same-day purchase for CGT purposes. This rule takes priority over all other matching rules. Its primary purpose is to prevent taxpayers from manipulating the timing of transactions within a single trading day to create artificial gains or losses. For example, if you sell 1,000 shares in the morning and buy 500 shares of the same company in the afternoon, 500 of the sold shares would be matched with the 500 repurchased shares under the same-day rule.

The 30-day bed and breakfast rule is the second HMRC share matching rule. It applies after the same-day rule and states that if you sell shares and repurchase shares of the same class in the same company within 30 days following the sale, the disposal is matched with the subsequent purchase. The rule was introduced to prevent investors from selling shares to crystallise a loss and immediately rebuying them, a practice historically known as bed and breakfasting. The practical consequence is that if you sell and rebuy within 30 days, any intended loss may be denied. To realise a genuine allowable loss, you must wait at least 31 days before repurchasing.

The Section 104 pool is the third and final HMRC share matching rule. After the same-day rule and the 30-day rule have been applied, any remaining shares to be matched are identified against the Section 104 pool. The pool operates as a rolling weighted average cost calculation for each holding of shares of the same class in the same company. Each time you buy additional shares, the shares and their cost are added to the pool, and the average cost per share is recalculated. When you sell shares matched to the pool, the acquisition cost is calculated using this average cost. This is the most commonly used matching rule for buy-and-hold investors.

To calculate capital gains on shares, you follow these steps: (1) identify each disposal made during the tax year; (2) apply HMRC's share matching rules (same-day, 30-day, and Section 104 pool) to determine which shares were sold and their acquisition cost; (3) subtract the acquisition cost and allowable expenses (broker fees, stamp duty) from the disposal proceeds to calculate the gain or loss on each disposal; (4) aggregate all gains and losses for the year; (5) offset current-year losses against gains; (6) apply any brought-forward losses; (7) deduct the annual exempt amount; and (8) apply the appropriate CGT rate to the remaining taxable gains. FiscalFox automates this entire process from your broker CSV files.

Yes. Allowable capital losses can be offset against capital gains to reduce your CGT liability. Current-year losses must be offset against current-year gains in full, even if this reduces your net gains below the annual exempt amount. You cannot choose to defer current-year losses. If your total losses exceed your total gains in a given year, the excess losses are carried forward to future years. Losses carried forward from previous years are applied differently: you only need to use enough to reduce your net gains to the level of the annual exempt amount, preserving the remainder for future use.

Yes. If your allowable capital losses exceed your chargeable gains in a tax year, the surplus losses can be carried forward indefinitely to use against future gains. However, there is an important condition: you must report the losses to HMRC within four years of the end of the tax year in which they arose, or you lose the right to carry them forward. Brought-forward losses are applied after current-year losses and need only be used to the extent that they reduce your net gains to the annual exempt amount. This provides flexibility in managing your tax position across multiple years.

It depends. Even if your net chargeable gains are below the annual exempt amount and no tax is due, you may still need to report your disposals to HMRC. GOV.UK says that if you are registered for Self Assessment, gains below the allowance still need reporting if the total amount you sold the assets for was more than £50,000 for the 2023/24 tax year onwards. You may also need to report to claim capital losses or if HMRC asks for details.

The SA108 is the Capital Gains Summary supplementary pages that form part of the HMRC Self Assessment tax return. It is where you report your capital gains and losses from the disposal of shares and other chargeable assets. The form includes sections for listed shares and securities, unlisted shares, and other assets. For share disposals, you need to provide the number of disposals, total disposal proceeds, total allowable costs, total gains, and total losses. FiscalFox generates summary figures that correspond directly to the relevant SA108 boxes, making it straightforward to complete the form accurately.

FiscalFox offers a free tier that allows you to upload your broker CSV files and view a summary of your capital gains calculations. You can see your total gains, total losses, and net position at no cost. To access the full detailed breakdown of every disposal, the HMRC-ready SA108 figures, and downloadable reports, a paid report is required. This one-time purchase gives you the complete computations for a specific tax year, including the detailed share matching workings for every disposal. There is no subscription; you only pay for the reports you need.

FiscalFox has built-in support for Vanguard Investor, Hargreaves Lansdown, Freetrade, Trading 212, eToro, InvestEngine, Moneybox, Saxo, and Interactive Brokers with automatic format detection. Unsupported broker files can use the Other Broker AI import path, which requires sign-in and consent before a file is sent for parsing.

FiscalFox applies the same calculation methodology specified by HMRC for computing capital gains on shares. This includes the correct application of the same-day rule, the 30-day bed and breakfast rule, and Section 104 pooling, in the prescribed order. The output figures are designed to correspond directly to the boxes on the SA108 supplementary pages. However, FiscalFox is a calculation tool and does not constitute tax advice. We recommend that if your tax situation is complex or you are unsure about any aspect of your return, you consult a qualified tax professional or accountant.

FiscalFox is designed with a privacy-first architecture. Built-in broker file processing happens within your browser using client-side computation. Unsupported broker AI imports are different: they are opt-in and may send the file to the parser after you consent. When you generate or save a report, calculated results are encrypted using AES-256-GCM encryption before storage. We use Supabase for secure authentication and Stripe for payment processing, and we do not sell your data.

FiscalFox accepts CSV and Excel files exported from your broker's platform. Each built-in broker has its own export process and FiscalFox automatically detects the format. You need to export the file that contains your complete transaction history for the relevant tax year, including both buy and sell transactions. The upload page provides specific instructions for each broker, including where to find the export option in your broker's website or app.

Yes. The FiscalFox CLI is a standalone command-line tool designed to be operated by AI coding agents such as Claude Code, Cursor, GitHub Copilot, and Windsurf. You give the agent your broker CSV or XLSX file and ask it to calculate your capital gains. The agent parses the file, normalizes the data into the standard format, and calls the FiscalFox CLI to run the HMRC-compliant calculation. No AI is involved in the tax calculation itself - the maths follows the same share matching rules as the web app. Any agent that can read files and run shell commands will work.

The FiscalFox CLI is a command-line version of the FiscalFox capital gains calculator. It uses the same HMRC-compliant engine as the web app, applying the same-day rule, the 30-day bed and breakfast rule, and Section 104 pooling in the correct order. It is designed for use with AI coding agents, which handle parsing your broker file while the CLI handles all the tax law. You install it with npm install -g fiscalfox or run it with npx. It outputs structured JSON results including disposals, Section 104 pool balances, SA108 box values, and estimated tax liability.