These adjustments are reported on the AMMA statement issued by ETF providers each year. They do not create immediate tax, but they affect how much capital gain (or loss) will be calculated when you eventually sell. Understanding how they work is part of accurate record keeping.
Key takeaway
When an ETF distribution includes tax-deferred or return of capital amounts, your cost base must be reduced by that amount. Failing to track these adjustments leads to incorrect capital gains calculations when you eventually sell.
This is general educational content, not personal financial advice or tax advice. Tax situations vary. Consult a registered tax agent for guidance specific to your circumstances.
What a Cost Base Is#
Your cost base is the amount used to calculate capital gain or loss when you sell an investment. For shares and ETF units, it begins as the purchase price plus acquisition costs (such as brokerage).
Example: You buy 500 ETF units at $20.00 each and pay $10 in brokerage. Your cost base is:
(500 × $20.00) + $10 = $10,010.
When you eventually sell, your capital gain or loss is calculated as:
Sale proceeds − Cost base = Capital gain (or loss)
If your cost base changes between purchase and sale, the gain or loss calculation changes accordingly.
Why ETF Distributions Can Reduce Your Cost Base#
Not all ETF distributions are straightforward income. Some distributions contain components that are not immediately taxable. Two common examples are:
Return of capital: the fund distributes some of the investors' own capital rather than income or gains. This is not assessable income (you are receiving your own money back). However, it reduces your cost base because the invested amount has effectively decreased.
Tax-deferred amounts: certain distributions from managed trusts are structured so that the tax liability is deferred to the future. These amounts are not included in your income in the year received, but they reduce the cost base, bringing forward the tax liability to the point of eventual sale.
Both types of distribution are flagged in the AMMA statement with specific labels, typically "tax-deferred amount" or "cost base reduction amount."
How the Adjustment Works#
The cost base adjustment is calculated per unit and then applied to your holdings.
Example:
You hold 500 units with a cost base of $20.00 per unit (total cost base: $10,000).
The AMMA statement shows a cost base reduction of $0.15 per unit.
Updated cost base per unit: $20.00 − $0.15 = $19.85.
Updated total cost base: 500 × $19.85 = $9,925.
When you eventually sell your 500 units at, say, $25.00 per unit ($12,500 total):
Capital gain = $12,500 − $9,925 = $2,575.
Without the adjustment applied, the incorrect calculation would be:
Capital gain = $12,500 − $10,000 = $2,500.
The difference is $75 in additional capital gain because the cost base was not properly reduced. Over years of holding with multiple adjustments, the cumulative error grows.
Upward Cost Base Adjustments#
Most common are reductions (downward adjustments). However, upward adjustments can occur under the AMIT regime in certain circumstances, such as when the fund's taxable income for the year exceeds the cash it distributed (the excess is attributed to investors for tax purposes, with a matching cost base increase).
An upward cost base adjustment means your recorded cost base increases. This reduces the future capital gain when you sell. The tax on the income was paid in the year of attribution, so the cost base increase prevents that income being taxed again as a capital gain.
Tracking Adjustments Across Multiple Purchases#
The cost base adjustment needs to be tracked for each parcel of units separately. If you have purchased units at different times and prices, each parcel has its own cost base.
Example:
| Parcel | Units | Cost Base Per Unit | Date Acquired |
|---|---|---|---|
| Parcel 1 | 200 | $18.00 | Jan 2022 |
| Parcel 2 | 300 | $21.00 | Aug 2023 |
If the AMMA statement shows a cost base reduction of $0.20 per unit, both parcels are adjusted:
| Parcel | Adjusted Cost Base Per Unit |
|---|---|
| Parcel 1 | $18.00 − $0.20 = $17.80 |
| Parcel 2 | $21.00 − $0.20 = $20.80 |
If you later sell only Parcel 1 (200 units), you use $17.80 per unit as the cost base for that parcel, not $21.00 and not an average.
This per-parcel tracking is also why DRP acquisitions (from distribution reinvestment plans) create additional parcels, each with their own cost base and acquisition date.
A Practical Record-Keeping System#
The minimum requirement is a spreadsheet with one row per parcel, updated annually:
| Column | Contents |
|---|---|
| ETF Name | Fund name or ASX code |
| Purchase Date | Date units were acquired |
| Units | Number of units in this parcel |
| Cost Base Per Unit | Starting cost, adjusted each year |
| Total Cost Base | Units × Cost base per unit |
| Notes | Source (purchase, DRP, etc.) |
After each AMMA statement:
- Identify the cost base adjustment amount per unit (upward or downward).
- Apply it to each parcel for that ETF.
- Update the cost base per unit column.
- Note the financial year and the adjustment source.
What Happens When the Cost Base Hits Zero#
If you hold an ETF for many years and receive many tax-deferred distributions, the cumulative reductions could, in theory, reduce a parcel's cost base to zero.
If additional reductions are reported after the cost base has reached zero, the ATO's general position is that those further reductions become immediately assessable as a capital gain. The tax that was being deferred can no longer be deferred because there is no remaining cost base to absorb it.
This is most likely to occur in funds with a high proportion of tax-deferred distributions (some property and infrastructure funds have historically had this characteristic). It is uncommon for standard equity index ETFs, where most distributions are income (dividends) rather than return of capital.
Tax Deferred Distributions and DRP#
If you participate in a DRP (distribution reinvestment plan) and part of the distribution is tax-deferred or a return of capital, the DRP creates a new parcel of units with its own cost base. The original parcels held prior to the distribution still receive the cost base reduction.
The new DRP parcel's cost base is the market value at which the DRP units were issued, regardless of any tax-deferred classification of the distribution. This is an area where record keeping becomes particularly layered, and maintaining accurate notes from each distribution event is worth the effort.
Summary#
ETF distributions can include tax-deferred or return of capital components that reduce the cost base of your units rather than being immediately taxable. These reductions are reported on AMMA statements issued annually by ETF providers. Failing to record them leads to understated capital gains when you eventually sell. Each parcel of units must be tracked separately, with annual updates applied from the AMMA statement. Upward adjustments (less common) increase the cost base and reduce future capital gain. For investors who hold ETFs for many years across multiple purchases and DRP reinvestments, maintaining a simple per-parcel spreadsheet is the most reliable approach.
Sources#
- Australian Taxation Office. (2024). Cost base of assets. https://www.ato.gov.au/individuals-and-families/investments-and-assets/capital-gains-tax/property-and-capital-gains-tax/cost-base-and-reduced-cost-base
- Australian Taxation Office. (2024). Attribution managed investment trusts for members. https://www.ato.gov.au/businesses-and-organisations/trusts/managed-investment-trusts/attribution-managed-investment-trusts/amit-for-members
- Australian Taxation Office. (2024). Return of capital. https://www.ato.gov.au/individuals-and-families/investments-and-assets/stocks-and-shares/return-of-capital