Capital Gains Tax Basics: How It Actually Works in Australia

Capital gains tax is one of those areas almost everyone has heard of and relatively few people fully understand, partly because it isn't actually a separate tax — it's simply the inclusion of a capital gain in your normal taxable income, taxed at your marginal rate. Understanding the mechanics properly removes a lot of the confusion around when it applies, how it's calculated, and what can reduce it.

What actually triggers capital gains tax

A capital gains tax (CGT) event is most commonly triggered by selling or otherwise disposing of an asset acquired after CGT was introduced in September 1985 — shares, an investment property, a business, or other significant assets. It can also be triggered by other events beyond a straightforward sale, such as an asset being lost or destroyed and an insurance payout received, or certain changes in ownership structure. The key point: it's the disposal event that triggers the calculation, not simply holding an asset that has increased in value.

How the gain is actually calculated

At its simplest, a capital gain is the difference between what an asset cost to acquire (the cost base) and what it sold for (the capital proceeds). The cost base isn't just the original purchase price — it can include incidental costs of acquisition and disposal (such as legal fees, stamp duty, and agent commissions) and, for some assets, capital improvements made over the period of ownership. Properly capturing everything that legitimately forms part of the cost base is one of the more overlooked ways to reduce a capital gain, since many people only think to claim the original purchase price.

The 50% CGT discount

For individuals and some other entities, if an asset has been held for at least 12 months before disposal, only 50% of the capital gain is included in assessable income. This is one of the most significant and widely used tax concessions available to individual investors, and the 12-month holding period is calculated precisely — disposing of an asset even a few days short of the full year can mean missing out on the discount entirely, so timing a sale around this threshold is worth deliberate attention when a sale date is flexible.

Capital losses — what they can and can't offset

If an asset is sold for less than its cost base, the result is a capital loss rather than a gain. Capital losses can only be offset against capital gains — not against other income like salary or business income — but they can be carried forward indefinitely to offset gains in future years if there isn't a gain to offset them against in the year they occur. This makes the timing of selling underperforming investments a genuine planning consideration, not just a loss to absorb passively.

The main residence exemption

For most people, their family home is exempt from capital gains tax entirely under the main residence exemption — this is one of the most valuable tax concessions available and applies automatically in most straightforward cases. However, this exemption can be partially or fully lost in certain situations: if part of the home was used to produce income (such as renting out a room, or running a business from a dedicated space, particularly where occupancy costs were claimed as deductions), or if the property wasn't the person's main residence for the entire period of ownership. Anyone who has rented out their home for a period, used part of it for business, or has more than one property that could be considered a residence should get this assessed properly rather than assuming the full exemption automatically applies.

Inherited assets and deceased estates

CGT rules around inherited assets have their own specific provisions, generally allowing a beneficiary to defer any capital gain until they eventually dispose of the inherited asset themselves, rather than triggering a CGT event purely on inheritance. The cost base used by the beneficiary depends on factors including when the deceased originally acquired the asset and whether it was their main residence — this is an area with enough nuance that it's worth specific advice rather than assumption, particularly for inherited property.

Shares, crypto, and other investments

The same fundamental CGT principles apply to shares, managed funds, and cryptocurrency as they do to property — acquisition cost, disposal proceeds, holding period for the discount, and so on. Cryptocurrency specifically is an area the ATO has significantly increased data-matching and review activity around in recent years, given the historical underreporting in this asset class, and every individual transaction (including crypto-to-crypto trades, not just cashing out to traditional currency) can potentially be a CGT event requiring its own calculation.

Record-keeping — the part that causes the most pain later

The single most common practical problem with capital gains tax isn't the calculation itself — it's not having kept adequate records of the cost base over what can be a very long ownership period, sometimes decades for a property or long-held shares. Purchase contracts, records of capital improvements, and any costs of acquisition and disposal should be retained for the entire period an asset is held, plus the required period after disposal, rather than assumed to be reconstructable from memory when the asset eventually sells.

How ATA Accountants can help

We help individuals understand their capital gains tax position before a sale happens, not just calculate it after the fact — including identifying everything that legitimately reduces a gain, confirming exemption eligibility, and planning disposal timing where it genuinely matters.

**Book an appointment** before selling a significant asset, so the capital gains position is understood in advance, not discovered at tax time.