Australia CGT Reform Calculator

Interactive one-page calculator and claim-check for Australia's capital gains tax debate.

Live site:

• https://australia-cgt-reform-calculator.setiyaputra.me

It compares:

• the current 50% CGT discount
• an illustrative inflation-indexed cost-base scenario
• full nominal taxation with no discount

It also includes:

• scenario presets labeled Realistic, Optimistic, and Exaggerated
• an optional advanced assumptions mode for grandfathering, Subdivision 152 settings, negative gearing offsets, and tax-rate presets
• a distributional fact section using official age and income split data
• a claim-pressure-test section for founder, ETF/property, housing-substitution, and distributional framing arguments
• a Which Claims Matter Most? 2x2 matrix for evidence strength vs policy importance
• direct references to PBO, Treasury, ABS, RBA, and ATO sources

Why this project exists

Australia's CGT debate is often argued in slogans.

This project exists to do two narrower jobs well:

1. show how different tax treatments change long-run compounding outcomes under explicit assumptions
2. separate claims that are strongly supported by official public data from claims that are still rhetorical, assumption-driven, or unresolved

The site is intentionally built as both:

• a calculator for worked scenarios
• a claim-check for distributional and policy arguments

It is not trying to settle every reform question. It is trying to raise the evidentiary standard of the discussion.

Reasoning behind the page

The page starts from a simple observation:

• a dramatic worked example can be mathematically correct and still be a weak guide to public policy if its assumptions are stretched
• a strong political claim can be emotionally compelling and still be weakly evidenced by the official data

So the project splits the problem into layers.

1. Mechanics layer

This is the compounding calculator itself.

It compares:

• current law with the 50% CGT discount
• an illustrative inflation-indexed cost-base treatment
• a no-discount reference case

That layer answers:

• how much do return assumptions matter?
• how much does inflation matter?
• how sensitive is the headline to holding period and tax rate?

2. Evidence layer

This is the claim-check side of the page.

It asks:

• who benefits from the current discount now?
• how concentrated are those benefits by income?
• what do official age splits show?
• which arguments are already well supported, and which still need more evidence?

3. Interpretation layer

The site makes a deliberate distinction between:

• directly supported
• illustrative but assumption-driven
• important but not yet proven with public data alone

That distinction matters because several common claims in the CGT debate are not equally strong.

For example:

• concentration of benefit at the top of the income distribution is strongly evidenced
• age distribution of benefit is supported by Treasury chart data
• precise claims about capital flight, startup damage, and behavioural response are more weakly evidenced from public aggregate data alone

Evidence model

The page uses an explicit evidence standard:

• Directly supported: official public data clearly measures the claim
• Illustrative: the math is transparent, but the scenario depends on assumptions
• Not yet proven: the claim may be plausible, but public official data does not cleanly establish it on its own

This is why the site includes both:

• scenario labels such as Realistic, Optimistic, and Exaggerated
• the Which Claims Matter Most? matrix

Key claims the page is testing

• Whether replacing the current CGT discount would materially change long-horizon outcomes for investors
• Whether the current discount is mainly a broad middle-class or young-household concession
• Whether the strongest current evidence points to a high-income and older-age concentration of benefits
• Which policy objections are already evidenced and which still require stronger empirical support

Stack

• Next.js 16
• React 19
• Tailwind CSS 4
• Cloudflare Pages

Local development

pnpm install
pnpm dev

Build:

pnpm build

Deploy

This project is deployed as a static export to Cloudflare Pages.

pnpm build
pnpm exec wrangler pages deploy out --project-name=cgt-compound-calculator

Sources used on-page

• Parliamentary Budget Office: Operation of the CGT discount
• Treasury: 2025–26 Tax Expenditures and Insights Statement
• Treasury TEIS chart-data workbook
• Australian Bureau of Statistics
• Reserve Bank of Australia
• Australian Taxation Office

Reference links

• PBO publication: https://www.pbo.gov.au/publications-and-data/publications/costings/operation-CGT-discount
• PBO PDF: https://www.pbo.gov.au/sites/default/files/2026-02/PBO%20-%20Operation%20of%20the%20CGT%20discount.pdf
• Treasury TEIS publication: https://treasury.gov.au/publication/p2025-721342
• Treasury TEIS chart-data workbook: https://treasury.gov.au/sites/default/files/2025-12/p2025-721342-chart-data.xlsx
• ABS Household Income and Wealth: https://www.abs.gov.au/statistics/economy/finance/household-income-and-wealth-australia
• ABS Housing Occupancy and Costs: https://www.abs.gov.au/statistics/people/housing/housing-occupancy-and-costs
• ABS Business Counts: https://www.abs.gov.au/statistics/economy/business-indicators/counts-australian-businesses-including-entries-and-exits/latest-release
• ABS Innovation in Australian Business: https://www.abs.gov.au/statistics/industry/technology-and-innovation/innovation-australian-business
• RBA Household Sector Chart Pack: https://www.rba.gov.au/chart-pack/household-sector.html
• ATO CGT statistics: https://www.ato.gov.au/about-ato/research-and-statistics/in-detail/taxation-statistics/taxation-statistics-2022-23/statistics/capital-gains-tax-statistics

Method note

• The calculator does not claim to model a final enacted reform package.
• The indexation comparison is illustrative unless and until a live proposal is published with exact legislative design.
• The page now includes an optional advanced assumptions mode for simplified modelling of Subdivision 152 settings, grandfathered-gain share, and negative gearing offsets, but it remains an approximation rather than a full tax engine.
• Age and income distribution sections rely on official public releases, but some stronger causal claims would still require custom tabulations, linked microdata, or restricted datasets.
• The detailed research framing for this repo is captured in: docs/shaping/2026-05-05-aus-gov-dataset-plan.md

Updates

• Add advanced scenario cards — added card-based UI for the advanced CGT scenario presets
• Add advanced CGT scenario controls — introduced controls for grandfathering, Subdivision 152, negative gearing offsets, and tax-rate presets in advanced assumptions mode
• Clarify CGT claim boundaries — tightened language around what the claim-check section does and does not establish from public data
• Update policy axis colors and social preview image — refreshed the 2x2 matrix colour scheme and the Open Graph preview image
• Document project reasoning and fix colored card backgrounds — added reasoning prose to the README and fixed card background rendering
• Initial site — launched the calculator with scenario presets, distributional fact section, claim-pressure-test section, and the 2x2 evidence matrix

Notes

• The calculator is a sensitivity tool, not tax or legal advice.
• The policy comparison is illustrative unless and until a final reform package is published.