A CLI tool to calculate UK Capital Gains Tax for share disposals using HMRC Same Day, Bed & Breakfast, and Section 104 matching rules.

The main idea is a small, line-based DSL that describes your transactions (buys, sells, dividends, splits) in a consistent format. You can write it by hand, or convert broker exports into this intermediate format and then generate CGT reports from it. Everything runs locally; your data is not uploaded anywhere.

brew tap velikodniy/tap
brew install cgt-tool
cgt-tool --version

Download the latest release for your platform from GitHub Releases.

chmod +x cgt-tool-*
./cgt-tool-linux-x86_64 --help

Requires Rust 1.85+ (2024 edition):

cargo install --path crates/cgt-cli

Convert broker data (optional):

cgt-tool convert schwab transactions.json --output transactions.cgt

Or write a small .cgt file:

2024-04-01 BUY AAPL 100 @ 150.00 USD FEES 5.00 USD
2024-06-20 SELL AAPL 50 @ 180.00 USD

Generate a report:

cgt-tool report transactions.cgt

Sample output:

Tax year    Gain     Proceeds   Allowance   Taxable
2024/2025   £1,200   £7,200     £3,000      £0

SELL 50 AAPL on 20/06/2024 - GAIN £1,200
  Section 104: 50 shares @ £120.00
  Proceeds: £7,200 | Cost: £6,000 | Gain: £1,200

Output formats: plain text (default), PDF (--format pdf), JSON (--format json).

You can pass multiple .cgt files if your broker limits export ranges (e.g., Schwab exports max 4 years):

cgt-tool report part1.cgt part2.cgt --format pdf --output report.pdf

• Your transactions: broker exports (preferred) or a hand-written .cgt file
• Full history for each holding (you need the buys before the sells; partial exports can produce incorrect gains)
• Fees/commissions where applicable (they affect the gain)
• For foreign assets: currency codes (otherwise values are treated as GBP)

• report: calculate gains/losses and produce plain text, PDF, or JSON
• convert: convert supported broker exports into the .cgt DSL
• parse: parse/normalize .cgt and print JSON (debugging and scripting)
• mcp: run an MCP server so AI apps can call the calculator

Run cgt-tool --help or cgt-tool <subcommand> --help for all options.

One transaction per line. Keywords are uppercase, placeholders are <angle brackets>, optional parts are [square brackets].

# Comment
2025-04-01 BUY AAPL 100 @ 150.00 FEES 5.00
2025-05-01 SELL AAPL 50 @ 160.00 FEES 5.00

BUY/SELL:    <date> BUY|SELL <ticker> <quantity> @ <price> [<currency>] [FEES <amount> [<currency>]]
DIVIDEND:       <date> DIVIDEND <ticker> TOTAL <value> [<currency>] [TAX <amount> [<currency>]]
ACCUMULATION:   <date> ACCUMULATION <ticker> <quantity> TOTAL <value> [<currency>] [TAX <amount> [<currency>]]
CAPRETURN:      <date> CAPRETURN <ticker> <quantity> TOTAL <value> [<currency>] [FEES <amount> [<currency>]]
SPLIT:       <date> SPLIT|UNSPLIT <ticker> RATIO <ratio>

• GBP is the default currency. Add ISO 4217 codes after amounts to use foreign currencies.
• The tool uses HMRC monthly average exchange rates for UK tax calculations.
• Bundled FX rates are updated regularly in releases to track the latest HMRC data.

FX rates source: UK Trade Tariff Exchange Rates

Use a custom folder with newer or missing rates:

cgt-tool report transactions.cgt --year 2024 --fx-folder ./my-rates

Download rates:

./scripts/download-fx-rates.sh
./scripts/download-fx-rates.sh ./my-rates

Transactions export (JSON):

• Accounts -> Transaction History
• Pick -> Brokerage Accounts in the main drop-down
• Click the download icon (top right) -> choose JSON

Awards export (for RSUs / FMV):

• Follow the steps above, but in the main drop-down choose -> Equity Awards Center

Convert to .cgt:

cgt-tool convert schwab transactions.json --output transactions.cgt

Schwab limits downloads to 4 years. If you need 5+ years, export multiple chunks, convert each, and report them together. The chunks must not overlap (otherwise you will duplicate transactions).

cgt-tool convert schwab schwab_2019_2022.json --output schwab_2019_2022.cgt
cgt-tool convert schwab schwab_2023_2026.json --output schwab_2023_2026.cgt
cgt-tool report schwab_2019_2022.cgt schwab_2023_2026.cgt

Supported transaction types:

• Buy/Sell transactions
• RSU vesting (Stock Plan Activity) with --awards Fair Market Value data
• Dividends (Cash Dividend, Qualified Dividend, Short/Long Term Cap Gain)
• Dividend tax withholding (NRA Tax Adj, NRA Withholding)
• Date formats: MM/DD/YYYY and as of MM/DD/YYYY

Unsupported/skipped:

• Wire transfers (Wire Sent/Received)
• Interest payments (Credit Interest)
• Stock splits (requires manual ratio entry)
• Other non-CGT-relevant transactions

Conversion examples:

# Basic conversion (transactions only)
cgt-tool convert schwab transactions.json

# With RSU vesting data (requires equity awards file)
cgt-tool convert schwab transactions.json --awards awards.json

# Save to file instead of stdout
cgt-tool convert schwab transactions.json --output output.cgt

• If numbers look wrong, check currency: amounts without a currency code are treated as GBP.
• UK tax years run 6 April to 5 April; use --year if you want to focus on a specific year.
• If you are missing buys (only have recent exports), your gains may be wrong because the matching rules require earlier acquisitions.

Embedded defaults for CGT exemption amounts live in crates/cgt-core/data/config.toml. Override locations: ./config.toml or ~/.config/cgt-tool/config.toml.

parse reads .cgt and prints normalized JSON. It is useful for sanity-checking your input and piping into tools like jq.

cgt-tool parse transactions.cgt | jq

For browser or Node.js usage (experimental). Download the .tgz from GitHub Releases and install:

npm install cgt-tool-wasm-<version>.tgz

See crates/cgt-wasm/README.md and web/ for full docs and the demo.

MCP (Model Context Protocol) is an open standard for connecting AI apps to external tools.

Start the server:

cgt-tool mcp

To connect it to clients like Claude Desktop, you typically add a small JSON config that points to the cgt-tool binary and passes mcp as an argument. See MCP’s client docs for step-by-step setup:

• What is MCP
• Connecting local servers (includes Claude Desktop setup)

For detailed CGT matching rules, see docs/tax-rules.md.

Tests and ideas reused from cgtcalc made this project possible.