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

For disposals of shares, funds, and ETFs from 30 October 2024 onwards, basic rate taxpayers pay 18% and higher/additional rate taxpayers pay 24% on gains above the annual exempt amount. Before that date, the rates were 10% and 20% respectively. The annual exempt amount for 2024/25 is £3,000.

What is the capital gains tax allowance for 2024/25?

The annual exempt amount (tax-free allowance) for the 2024/25 tax year is £3,000. This is the same for 2025/26. It was reduced from £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?

You need to complete the SA108 supplementary pages if your total disposal proceeds exceed 4 times the annual exempt amount (£12,000 for 2024/25), if you have chargeable gains above the annual exempt amount, or if you want to claim capital losses.

What is the best capital gains tax calculator for UK shares?

FiscalFox is a specialist UK capital gains tax calculator for share investors. It applies all three HMRC share matching rules automatically - same-day rule, 30-day bed and breakfast rule, and Section 104 pooling - and generates SA108-ready reports. It supports Vanguard, Hargreaves Lansdown, Freetrade, Trading 212, eToro, InvestEngine, Moneybox, Saxo Bank, and Interactive Brokers natively, plus any other broker via AI-powered CSV import.

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 capital gains for 2024/25 or 2025/26 are under the GBP 3,000 annual exempt amount, you do not owe CGT. However, you may still need to file SA108 if your total disposal proceeds exceed GBP 12,000 (4 times the exemption), or if you want to claim capital losses to carry forward.

How do I calculate capital gains on shares?

Capital gains on shares are calculated as disposal proceeds minus allowable costs (purchase price plus dealing fees). HMRC requires you to identify which shares are being sold using share matching rules: same-day rule first, then the 30-day bed and breakfast rule, then Section 104 pooling. FiscalFox automates this entire process.

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. You can upload transaction files from up to 2 platforms, calculate your gains and losses, and view results at no cost. The premium tier (£29.99 per tax year) is only needed for exporting HMRC-ready reports and unlimited platform support.

Do you support my broker?

FiscalFox works with any broker. We have built-in support for Vanguard, Hargreaves Lansdown, Freetrade, Trading 212, eToro, InvestEngine, Moneybox, Saxo Bank, and Interactive Brokers with automatic format detection. For any other broker, our AI-powered parser automatically detects your CSV column layout and imports your transactions securely.

Is FiscalFox HMRC-compliant and secure?

Yes. FiscalFox applies all three HMRC share matching rules in the correct priority order. All data is encrypted using AES-256-GCM, transaction files are processed client-side in your browser, and no files are stored in our databases.

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 upgrade to Premium?

The free tier lets you calculate and view your capital gains on-screen. Upgrade to Premium (£29.99 per tax year, one-time payment) when you want to download HMRC-ready PDF and CSV reports for your Self Assessment.

Is there a subscription?

No. Premium is a one-time payment per tax year. Pay £29.99 once and download your reports as many times as you need for that tax year. There are no recurring charges or hidden fees.

Can I use FiscalFox with Claude Code or another AI agent?

Yes. The FiscalFox CLI is a standalone command-line tool designed for AI coding agents such as Claude Code, Cursor, GitHub Copilot, and Windsurf. You give the agent your broker file and it handles parsing, normalizing, and calculating your capital gains using HMRC share matching rules. No AI is involved in the tax calculation itself.

What is the FiscalFox CLI?

The FiscalFox CLI is a command-line version of the FiscalFox calculator. It uses the same HMRC-compliant engine as the web app. Install it with npm install -g fiscalfox or run with npx. It outputs structured JSON results including disposals, Section 104 pool balances, SA108 box values, and estimated tax liability.

FiscalFox for Firms - Multi-Client CGT Software for Accountants

Individual-first CGT workflow

Still built first for people completing their own tax return

FiscalFox's core product is for UK investors who need to calculate capital gains, check HMRC share-matching rules, and prepare figures for Self Assessment. The practice workflow exists so accountants can support those same individuals when they bring broker exports, SA108 questions, or complex portfolios to the firm.

What individual users get

On-screen CGT calculation before paying for reports
Broker CSV imports and HMRC matching rules handled for them
SA108-ready outputs for Self Assessment

Calculate your gains as an individual

The Problem with Manual CGT Processing

ISIN Mapping Pain

Each broker uses different security identifiers. Manually mapping ISINs, tickers, and fund names across platforms is error-prone and time-consuming.

Corporate Action Gaps

Stock splits, mergers, and reorganisations break Section 104 pool calculations. Most tools can't handle them automatically.

Multi-Client Bottleneck

Processing CGT for multiple clients one at a time - uploading files, checking results, generating reports - creates a seasonal bottleneck every January.

Built for Tax Practices

Multi-Client Management

Add clients, switch between them instantly, and keep every portfolio isolated with its own data and reports.

SA108 Batch Reports

Generate SA108 supporting schedules, detailed computations, and audit trails for every client - individually or in bulk.

AI Broker Parsing

Upload any broker file format - CSV, Excel, PDF. Our AI (Gemini 2.5 Flash) extracts transactions automatically.

Joint Portfolio Splitting

Jointly-held portfolios? Upload once, split gains by ownership percentage. Each co-owner gets their own report.

Full Audit Trail

Every calculation is traceable. Same-day rule, 30-day rule, Section 104 pool movements - all documented per HMRC guidelines.

ISIN Resolution

Automatic ISIN, ticker, and security name matching across brokers. Ambiguous matches flagged for your review.

How It Works

Step 1

Start with a client file

Use the same upload-first workflow individual investors use when preparing their Self Assessment figures.

Step 2

Review the calculation

Check disposals, matching rules, Section 104 pool movements, and supporting evidence before anything is filed.

Step 3

Prepare client outputs

Generate HMRC-ready figures and reports that help individuals complete SA108 accurately.

Practice Access

For firms and advisers

Discuss practice workflows with us

Firm access is handled through conversation rather than a public self-serve plan. That keeps the product honest while we learn what accountants need for client review, report packs, permissions, and seasonal CGT workflows.

Client CGT review workflows
SA108 supporting schedules
Broker import coverage
Audit trail expectations
Joint portfolio handling
Practice reporting needs

Individual investors can still calculate their own CGT from the dashboard.

FiscalFox vs Alternatives

Feature	FiscalFox	CCH CGT Module	Spreadsheet
Multi-client management			-
AI broker file parsing		-	-
Any broker format		-	-
SA108 reports			-
Joint portfolio splitting		-	-
ISIN auto-resolution		-	-
Bulk export (ZIP)			-
Stock split handling			-
Setup time	5 min	Days	Hours

HMRC Compliance

Calculations follow TCGA 1992 share matching rules: same-day (s.105), 30-day bed & breakfast (s.106A), and Section 104 pools.
Reports align with HMRC Capital Gains Manual guidance (CG51560, CG51550, CG15800).
Data processed and stored securely. All client data is isolated per firm and per client.

Ready to streamline CGT for your practice?

Tell us how your firm handles client broker files and we can discuss whether FiscalFox fits your workflow.

Capital Gains Tax Software for Accounting Practices