A worked example
On 15 August 2023 you buy 1,000 units of an ETF at $80, with $10 brokerage: a cost base of $80,010. On 20 September 2025 you sell all 1,000 at $100, paying $10 brokerage: capital proceeds of $99,990.
- Capital gain: $99,990 − $80,010 = $19,980.
- Held from 15 August 2023 to 20 September 2025, more than 12 months, so the 50% discount applies: $9,990.
- Net capital gain for 2025–26: $9,990.
- With other taxable income of $90,000, the extra income falls in the 30% bracket, so the extra tax is about $2,997 plus $199.80 Medicare levy: about $3,197.
Had you sold on 15 August 2024, exactly one year after buying, there would be no discount: the 12 months exclude the day you bought and the day you sold, so the earliest qualifying date was 16 August 2024.
How the calculation works
- Capital proceeds. What you received for the asset, less selling costs such as brokerage or the agent's commission.
- Cost base. What it cost you: the purchase price plus incidental costs of buying it (brokerage, stamp duty, legal fees), and for property, capital improvements.
- Gain or loss. Proceeds minus cost base, for each parcel sold.
- Losses. Capital losses carried forward from earlier years and losses made this year are taken off this year's gains. The ATO says you can choose which gains they reduce; taking them off gains that do not get the discount first gives the lowest result, and that is what the calculator does.
- Discount. Australian-resident individuals halve what is left of each gain on an asset owned for at least 12 months, counting from the day after acquisition to the day before the CGT event.
- Net capital gain. The total goes in your tax return and is taxed at your marginal rate along with your other income. A net capital loss cannot reduce other income; it carries forward.
Matching parcels
If you bought the same shares several times, a partial sale has to be matched to parcels. The calculator offers:
- First in, first out (FIFO): the oldest parcels go first. Most likely to qualify for the discount.
- Last in, first out (LIFO): the newest parcels go first.
- Highest cost first: the most expensive parcels go first, which minimises the gain (but may pick parcels held under 12 months).
- Specific parcels: you choose which parcel each sale came from, as the ATO allows when your records identify them (your CHESS or issuer-sponsored statements usually do).
The FIFO vs specific identification guide shows how much the choice can matter.
DRPs, splits and other events
Enter each dividend reinvestment as a DRP: a new parcel dated the allotment date, costing the reinvested amount. Enter splits and consolidations with the ratio of new units per old unit (2 for a 2-for-1 split, 0.1 for a 1-for-10 consolidation); the cost base and acquisition dates carry over. Returns of capital, demergers, takeovers paid in scrip, and rights issues change cost bases in ways this calculator does not model; note them for your accountant.
Records to keep
Keep contract notes for every buy and sell, DRP statements, and corporate-action notices, for at least five years after the last sale of a holding. They are what proves your cost base if the ATO asks, and what lets you use specific identification.
Common mistakes
- Forgetting DRP parcels, so the cost base is too low and the gain too high.
- Using the settlement date instead of the trade date for the financial year.
- Selling a few days before the 12-month mark and losing half the discount.
- Not carrying forward last year's capital loss.
Checking the result before you lodge
A calculator is only as good as the figures you give it. Before copying anything into your tax return, run through these checks:
- Holdings reconcile. The units left over after every sale should match what your broker, share registry or exchange says you still hold. If they do not, a buy, DRP or split is missing, and the cost base of some sale is wrong.
- Dates are trade or contract dates. Settlement dates move sales across 30 June and across the 12-month mark.
- Costs are on the right side. Purchase costs belong to the buy; selling costs belong to the sale. Entering both on one side gives the same gain but the wrong cost base for the parcels that are left.
- Losses brought forward match last year's return. The figure at label V of last year's return is this year's starting point.
- Pre-filled data. The ATO pre-fills some share and crypto data from brokers and exchanges. It often lacks cost bases, so treat it as a list of sales to account for, not as the answer.
If a disposal looks wrong, open its parcel breakdown in the year view: each line shows the parcel, its acquisition date, days held and cost base, which is usually enough to spot the missing or mistyped transaction.
Where the rules come from
The discount, the 12-month counting rule, the treatment of losses and the tax rates are taken from the ATO's published guidance, listed under sources below with the date they were last checked. Rates are stored per financial year and updated each July. Where a rule could not be confirmed against an official page, it is marked as unverified in the calculator's notes and in the schedule, so you and your accountant know what to check.