How the Capital Gain Tax Indexation Method Works

The capital gain tax indexation method adjusts an asset’s original cost for inflation, so you are taxed only on the real increase in value rather than on gains that partly reflect a falling dollar. Australia is the principal country still offering it, and only for assets acquired before 11:45 am AEST on September 21, 1999. India used a similar system for decades and removed it for most assets in 2024. The United States has never adopted indexation.

How the Inflation Adjustment Works

The idea is straightforward. If you bought an asset for $50,000 and later sold it for $80,000, some of that $30,000 gain is genuine appreciation and some is just the fact that a dollar buys less than it used to. Indexation inflates your original cost to reflect today’s dollars, so the taxable gain shrinks to the real gain.

The mechanics rely on a consumer price index. Divide the CPI figure at a specified endpoint by the CPI figure for the quarter you bought the asset. That gives you an indexation factor. Multiply the factor by your original cost, and you have your indexed cost base. Subtract that larger number from the sale price to get the taxable gain.

Who Can Still Use Indexation in Australia

Three conditions have to be met. The asset must have been acquired before 11:45 am AEST on September 21, 1999. You must have held it for at least 12 months before selling. And you must be an individual, a trust, or a complying superannuation fund. Companies can also use indexation, and because they cannot claim the CGT discount, indexation is their only inflation adjustment for pre-1999 assets.¹²

The critical limitation is the freeze. Indexation stops at the September 1999 quarter. Even if you hold the asset until 2026 or later, the CPI in the formula never advances beyond that quarter, so inflation after September 1999 gives no additional benefit.³

Calculating the Indexed Cost Base

The formula is fixed and the rounding rules are strict.

Start with your cost base: the original purchase price plus incidental expenses such as brokerage, stamp duty, or legal costs.
Find the CPI for the quarter in which you acquired the asset, using the ATO’s published CPI tables.
Divide 68.7 (the CPI for the September 1999 quarter and the frozen endpoint) by that figure. The result is your indexation factor.
Round the factor to three decimal places. If the fourth decimal is five or higher, round up. So 1.4125 becomes 1.413.
Multiply each eligible cost element by the factor. This applies to the purchase price and to incidental costs and capital improvements incurred before the September 1999 freeze.
Subtract the indexed cost base from the sale price. That is your indexed capital gain.

A worked example. You bought shares for $40,000 in the June 1993 quarter, when the CPI was 56.2. Dividing 68.7 by 56.2 produces 1.222 (rounded from 1.22241…). Multiplying $40,000 by 1.222 gives an indexed cost base of $48,880. If you sell for $70,000, your taxable gain is $21,120 rather than the nominal $30,000.³

One rule catches people out. If your indexed cost base exceeds the sale price, you cannot use indexation to create or increase a capital loss. You would fall back on the unindexed cost base to work out any loss.²

Indexation or the CGT Discount

If your asset qualifies for indexation, it almost certainly qualifies for the CGT discount too. Individuals and trusts get a 50 percent discount; complying super funds get 33.33 percent. You can use whichever method produces the smaller gain, but not both.¹

The ATO notes that in most cases the 50 percent discount gives a better result than indexation. The math explains why: indexation uses CPI data frozen in 1999, while the discount halves whatever your full nominal gain happens to be. The longer you have held the asset past 1999, the more the discount pulls ahead, because that post-1999 inflation goes unadjusted.²

Indexation can win when you have capital losses to offset. The CGT discount applies after capital losses are subtracted, so losses are used up at full value against the full nominal gain before the 50 percent reduction. Under indexation, the gain is smaller from the start, and your losses stretch further. If you are carrying significant capital losses from other disposals, run both calculations before you choose.

Records and Reporting

Keep everything that feeds the calculation: purchase receipts, records of incidental costs, the CPI figures you used, and the arithmetic itself. The ATO requires you to retain these records for at least five years after the relevant CGT event. If you apply a net capital loss from the disposal against a future year’s return, keep the records until the review period ends for the year in which the loss is fully used.⁴

You report the net capital gain on your tax return after completing the calculation. myTax has fields for capital gains, and entities with more complex situations may need to complete a separate capital gains tax schedule. The figure the ATO wants is the final net capital gain after you have chosen either the indexation or the discount method.

What Changed in India

India ran its own indexation system for decades, using a Cost Inflation Index published each year by the Central Board of Direct Taxes. Taxpayers adjusted their purchase price with the index and paid 20 percent on the indexed long-term gain. Unlike Australia’s, India’s index was updated annually rather than frozen.

The 2024 Union Budget changed the rules. For assets transferred on or after July 23, 2024, long-term capital gains are taxed at a flat 12.5 percent without indexation. The indexation benefit is no longer available for most asset classes. A narrow exception remains: resident individuals and Hindu Undivided Families who acquired land or a building before July 23, 2024 can choose between the new 12.5 percent rate without indexation and the old 20 percent rate with indexation, whichever produces the lower tax.⁵

For property acquired long ago at a low price, the old 20 percent-with-indexation route may still produce the smaller bill, especially where cumulative inflation has been substantial. Run both calculations before filing.

Why There Is No US Version

The United States has never adopted an indexation method for capital gains. The federal system instead distinguishes short-term from long-term gains based on holding period, taxing assets held one year or less at ordinary rates and giving longer holdings preferential rates.⁶

Indexing has been debated in Congress since at least 1978, when the House passed an indexing provision that was dropped from the final Revenue Act. The Senate adopted a similar provision in 1982 that was removed in conference. In 1992, an attempt to bring in indexation through Treasury regulations was rejected after the Department of Justice concluded Treasury lacked the authority to do it unilaterally. Bills have been introduced repeatedly since, most recently in 2018, but none has been signed into law.⁷

If you are a US taxpayer looking for the indexation method, it does not exist in federal law. The preferential long-term rates are the rough substitute, and cost basis can still be increased by purchase-related expenses such as brokerage commissions, transfer fees, and, for real estate, closing costs and title insurance. Those additions reflect money actually spent rather than an inflation adjustment, but they reduce taxable gain in a similar direction.⁸

1
Australian Taxation Office. CGT Discount
2
Australian Taxation Office. Indexing the Cost Base
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Australian Taxation Office. The Indexation Method
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Australian Taxation Office. Keeping Records
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Income Tax Department India. Capital Gain
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Office of the Law Revision Counsel. 26 USC 1 – Tax Imposed
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Congress.gov. Indexing Capital Gains Taxes for Inflation
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Internal Revenue Service. Topic No. 703, Basis of Assets