Capital Gains Tax Calculator

Compute capital gains tax with country presets (US, UK, Australia, Ireland, South Africa) or custom rules. Includes basis, exemptions, losses, and holding period.

How the presets behave

The calculator seeds default rates for the most common jurisdictions. Tweak allowances, exclusions, and the AU/ZA toggles to reflect local guidance.

How to Use This Calculator

Enter the sale proceeds, basis, and any transaction costs. Add exclusions for reliefs, realized losses, and the annual allowance to reduce the taxable gain. Choose a holding period, jurisdiction preset, and the rates that reflect your filing status, then click Calculate to see the estimated tax and after-tax proceeds.

The tool ships with editable presets that pre-load common rates and allowances—switch to CUSTOM to experiment with your own inputs.

Methodology

Gain is sale proceeds minus basis and selling costs. Exclusions, allowances, and losses reduce the candidate taxable gain, which is then subject to either the long-term or short-term rate. Optional Australian and South African adjustments modify the taxable basis before the marginal rate is applied, which keeps the model aligned with the original engine.

Why this calculator

  • Country presets with fully editable rates for transparency.
  • Models basis, costs, exemptions, allowances, and losses.
  • Clear formulas, sources, and a printable summary.

Related tax tools

Full original guide (expanded)

The full audit materials, formulas, citations, and changelog from the legacy page remain preserved above. Refer to those sections for precise LaTeX formulas, authoritative sources, and verification notes from Ugo Candido (2026-01-19).

Formulas
Gain = Psale − (Bcost + Csell)
\[ \textbf{Gain} = P_{\text{sale}} - \big( B_{\text{cost}} + C_{\text{sell}} \big) \]
Net gain before reliefs = max(0, Gain − exclusions)
\[ \textbf{Net Gain Before Reliefs} = \max(0,\ \text{Gain} - E_{\text{exclusions}} ) \]
Taxable gain = max(0, Net gain before reliefs − allowance − losses)
\[ \textbf{Taxable Gain} = \max\big(0,\ \text{Net Gain Before Reliefs} - A_{\text{allowance}} - L_{\text{losses}}\big) \]
Jurisdiction adjustments apply per preset (US short/long, UK asset bands, AU discount, IE/ZA inclusions).
\[ \textbf{Taxable Gain}_{\text{adj}} = \text{adaptive} \quad ; \quad \textbf{Tax} = \text{Taxable Gain}_{\text{adj}} \times t \]
The after-tax proceeds equal sale price minus the estimated tax.
\[ \textbf{After-Tax Proceeds} = P_{\text{sale}} - \text{Tax} \]
Citations
Changelog
  • 0.1.0-draft — 2026-01-19: Initial audit spec draft generated from HTML extraction (review required).
  • Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
  • Confirm sources are authoritative and relevant to the calculator methodology.
Verified by Ugo Candido Last Updated: 2026-01-19 Version 0.1.0-draft
Version 1.5.0