How the Attribution Managed Investment Trust rules quietly change your ETF cost base every year, and what it means when you sell.
For all the talk of ETFs being simple, their tax mechanics are anything but. Most Australian ETFs run through a special tax regime called the Attribution Managed Investment Trust, usually shortened to AMIT. The good news is that you do not have to understand every line of the legislation. The important part is what it does to your cost base, because it determines how much capital gains tax you eventually pay when you sell. This guide is general information rather than financial or tax advice.
A traditional trust passes through to investors whatever it actually pays out. AMIT lets a fund attribute taxable components to investors based on a clearly defined character, even if those components do not exactly match the cash distribution. That is why some ETFs may distribute, say, $1.00 per unit in cash but attribute $0.95 of taxable income, or attribute $1.05 against $1.00 distributed. The difference shows up in an annual cost base adjustment. The ATO's overview of attribution under the AMIT rules is set out on its investing in shares and managed fund pages.
Each year your fund sends an AMIT Member Annual statement, almost always called an AMMA. It lists the components attributed to you for the income year, including Australian dividend income, franking credits, foreign income, capital gains and other amounts, plus the net cost base adjustment for the year. You include the income components in your tax return, and you carry the cost base adjustment back to your records of each parcel of units you hold.
| Item on the AMMA | What it tells you |
|---|---|
| Attributed Australian income | Dividends, interest and other Australian income to include in your return |
| Franking credits | Imputation credits attached to franked dividends |
| Attributed foreign income | Overseas dividends and other foreign income, often with foreign tax offsets |
| Net capital gain attribution | Realised gains inside the fund passed through to you, with discount components separated |
| Net AMIT cost base adjustment | The amount you add to or subtract from your unit cost base |
The cost base adjustment exists to make sure income is not effectively taxed twice. Suppose your ETF attributes $1.05 of taxable income for the year but only distributes $1.00 in cash. The extra $0.05 has already been picked up in your tax return as income, so the rules increase your cost base by $0.05 per unit. When you eventually sell, that higher cost base reduces your capital gain. The reverse can happen too: if cash distributions exceed attributed income, your cost base typically falls, which increases your eventual capital gain. The adjustment is calculated per parcel rather than across your whole holding, which is why parcel-level records matter.
When you eventually sell ETF units, the capital gain is broadly the proceeds less the adjusted cost base of the parcels you sold, after applying any incidental costs of acquisition and disposal. For Australian resident individuals and trusts, the general 50% CGT discount can apply where a parcel has been held for more than 12 months. The result is added to your other taxable income and taxed at your marginal rate. Where the cost base has been adjusted upward over the years, the gain is smaller; where it has been adjusted downward, the gain is larger.
| Step | Calculation |
|---|---|
| 1. Start with cost base | Purchase price plus incidental costs (brokerage, transfer fees) |
| 2. Apply AMIT adjustments | Add upward adjustments, subtract downward ones, year by year |
| 3. Sale proceeds | Sale price less selling brokerage |
| 4. Capital gain | Proceeds minus adjusted cost base |
| 5. Apply 50% discount if eligible | Australian resident individuals/trusts, parcel held more than 12 months |
Because adjustments are per parcel and accumulate over years, the practical challenge with ETF investing is record keeping. If you buy small parcels regularly, including via dividend reinvestment plans, you can end up with dozens of parcels each carrying its own running cost base. Many investors use a broker-supplied tax report, an accountant or a portfolio tracking service to manage this. Whoever does the work, the legal responsibility for an accurate return rests with you.
Australian-domiciled ETFs that hold international shares operate under the same AMIT framework. Their AMMA statements typically include foreign income and foreign income tax offsets in addition to any franked Australian dividends. The cost base mechanics are identical, just with a wider mix of components. ETFs you hold directly on a foreign exchange follow different rules and can have their own quirks, which is another reason most beginners stick with Australian-domiciled funds.
A few practical traps catch ETF investors out. The first is treating the cash distribution as the assessable amount. It often is not. The amount you include in your tax return is the attributed amount from the AMMA, not the dollars that landed in your account. The second is forgetting the cost base adjustment. If you only update your records when you buy or sell, the years in between quietly drift away from the true position, and the eventual capital gain calculation overstates or understates the tax. The third is selling without considering which parcels you are selling. Where you have multiple parcels with different acquisition dates and cost bases, choosing which to sell can materially change the result, especially around the 12-month CGT discount threshold.
For a single ETF held for a year or two the maths is manageable. The picture changes when you have several AMIT funds, regular contributions, dividend reinvestment, and a sale that involves matching parcels to manage tax. At that point the cost of an accountant or a portfolio tracking service is usually small compared with the value of an accurate, defensible CGT calculation, particularly given the records must be kept and produced if the ATO asks.
Disclaimer: This article is general, educational information and not tax or financial advice. AMIT rules are detailed and individual outcomes depend on your records and circumstances. Check your fund's AMMA statement and the ATO investments and assets pages, and consider getting tailored advice.