# CGT Calculator — UK Capital Gains Tax Calculator

> Free online UK Capital Gains Tax calculator for stocks, options, and forex. Implements HMRC share matching rules (Same Day, Bed & Breakfast, Section 104 Pool), handles 60+ option strategies as separate CGT assets, supports 5 brokers (IBKR, Schwab, Trading 212, Freetrade, Morgan Stanley), and includes automatic FX conversion and ERI (Excess Reportable Income) for offshore funds. Calculations run in your browser.

CGT Calculator (cgtcalculator.io) helps UK taxpayers calculate capital gains tax on investment transactions. It applies HMRC rules precisely: each disposal is matched using the Same Day Rule, Bed & Breakfast Rule (30-day), and Section 104 Pool in strict order per CG51560. The output maps directly to Self Assessment form SA108.

The calculator is particularly strong on options trading — each option contract is treated as a separate CGT asset (never pooled) per HMRC CG12300. It correctly handles exercise, assignment, expiry, and cross-tax-year premium taxation for 60+ strategies including covered calls, iron condors, butterflies, straddles, spreads, and more.

## Documentation

- [How It Works](https://cgtcalculator.io/docs#how-it-works): Overview of the calculation pipeline — upload CSV, parse, convert FX, apply HMRC matching rules, generate report
- [Share Matching Rules](https://cgtcalculator.io/docs#matching-rules): Same Day Rule, Bed & Breakfast Rule (30-day), Section 104 Pool — with HMRC references CG51560, CG15155, CG15250
- [Options Trading](https://cgtcalculator.io/docs#options): How HMRC taxes options — writing, buying, exercise, assignment, expiry, cross-tax-year trades. 60+ strategies supported with per-leg CGT treatment per CG12300, CG12312, CG55590
- [Corporate Actions](https://cgtcalculator.io/docs#corporate-actions): Stock splits, cash mergers, spin-offs, ticker renames, return of capital
- [FX Trading](https://cgtcalculator.io/docs#fx-trading): Foreign exchange as "Other Assets" on SA108, with Same Day/B&B/S104 matching per CG78300
- [ERI / Offshore Funds](https://cgtcalculator.io/docs#eri): Excess Reportable Income for 550+ Vanguard and iShares funds, automatic cost basis adjustments per HS265
- [Dividends & Interest](https://cgtcalculator.io/docs#income): Dividend tax bands, withholding tax, treaty relief rates, interest with Personal Savings Allowance
- [Residency Status](https://cgtcalculator.io/docs#residency): UK resident, non-resident, temporary non-resident rules per TCGA92 s1A
- [Supported Brokers](https://cgtcalculator.io/docs#brokers): IBKR, Schwab, Trading 212, Freetrade, Morgan Stanley — CSV export instructions and multi-broker consolidation
- [Report Output](https://cgtcalculator.io/docs#output): SA108-ready report with full audit trail, matching breakdown, and PDF download

## Key Pages

- [Home](https://cgtcalculator.io/): Product overview, feature showcase, option strategy grid, pricing
- [Calculator App](https://cgtcalculator.io/app): Upload broker CSVs and generate your CGT report
- [ERI Reference Data](https://cgtcalculator.io/eri-reference-data): Browsable ERI per-unit data for Vanguard and iShares funds
- [Terms of Use](https://cgtcalculator.io/terms): Privacy and disclaimer information

## Option Strategies Supported

The calculator handles 60+ option strategies with correct per-leg HMRC tax treatment. Each option is a separate CGT asset per CG12300. Key strategies include:

Single-leg: Covered Call, Cash-Secured Put, Protective Put, Long/Short Call, Long/Short Put.
Vertical spreads: Bull Call, Bear Call, Bull Put, Bear Put, Ladders.
Calendar and diagonal: Calendar Call/Put, Diagonal Call/Put, Double Diagonal.
Butterflies: Long/Short Call/Put Butterfly, Iron Butterfly, Inverse Iron Butterfly.
Condors: Long/Short Call/Put Condor, Iron Condor, Inverse Iron Condor.
Straddles and strangles: Long/Short Straddle, Long/Short Strangle, Covered Short Straddle/Strangle, Guts.
Combos: Collar, Long/Short Combo, Jade Lizard, Reverse Jade Lizard, Synthetic Future/Put, Strap, Strip.
Ratio and broken wing: Call/Put Ratio Spread, Call/Put Ratio Backspread, Call/Put Broken Wing.

## HMRC Rule References

- CG51560: Share identification (matching) rules — Same Day, Bed & Breakfast, Section 104 Pool
- CG15155: Allowable acquisition costs (fees, commissions, stamp duty added to cost basis)
- CG15250: Allowable disposal costs (fees, commissions deducted from proceeds)
- CG12300: Options as separate CGT assets; exercise adjusts stock cost basis
- CG12312: Writing an option is a disposal (premium = proceeds on grant date)
- CG55590: Tax treatment of option grantor (premium as disposal proceeds)
- CG78300: Foreign exchange as chargeable assets
- CG78310: Foreign currency conversion rules
- HS265: Offshore funds — Excess Reportable Income guidance
- TCGA92 s1A: Territorial scope of CGT (residency)
- TCGA92 s10A / CG26500: Temporary non-residents anti-avoidance

## Optional

- [Terms of Use](https://cgtcalculator.io/terms): Privacy policy and legal disclaimer
- [ERI Reference Data Viewer](https://cgtcalculator.io/eri-reference-data): Browse raw ERI per-unit figures for all bundled offshore funds