Here's the honest answer up front: there isn't a universal winner. Which method costs less tax depends on your specific property. What matters is understanding both methods well enough to check, because only one of them gives you a choice.
Method 1: The Certified Valuation
You engage a registered valuer to certify what your property was worth on 1 July 2027. That figure becomes the dividing line: everything gained before it falls under the old 50% discount rule; everything gained after it falls under the new inflation-adjustment rule.
This method reflects reality: whatever your property actually did, good years and flat years included.
Method 2: The ATO's default formula
If you don't have a valuation, the tax office splits your gain a different way based purely on how long you owned the property before vs. after 1 July 2027. It assumes your property grew in value at a steady, even rate across the entire ownership period.
It's quick, and it needs no paperwork. But it can't see whether your property actually grew early, late, or somewhere in between because it isn't designed to.
A worked example
Here's the property we're using for this example:
| Purchase price | $500,000 |
|---|---|
| Purchase date | 1 July 2018 |
| Certified valuation | $1,200,000 |
| Valuation date | 1 July 2027 |
| Sale price | $1,600,000 |
| Sale date | 1 July 2034 |
| Tax rate used | 45% (top marginal rate) |
| CPI assumption | 4% per year |
| Step | With the certified valuation | Without it (ATO default) |
|---|---|---|
| Gain before 1 July 2027 | $1,200,000 − $500,000 = $700,000 | ≈ $618,700 (a rough 9/16 time split) |
| Taxable amount (50% discount applies) | $350,000 | $309,351 |
| Cost base adjusted for inflation over 7 years | $1,200,000 → $1,579,161 | $1,118,703* → $1,472,176 |
| Taxable amount left over after that adjustment | $20,839 | $127,824 |
| Total taxable gain | $370,839 | $437,175 |
| Tax owed at 45% | $166,878 | $196,729 |
Result: the certified valuation wins by $29,851.
Change the numbers, a different purchase price, a different holding period, a different growth pattern, and the result can go the other way just as easily. The ATO's default method sometimes comes out cheaper, particularly when a property's value grows relatively slowly in the years after the cutoff, since indexation can end up covering most or all of that gain either way.
Why this matters
The value of a certified valuation isn't that it always saves you money; it's that it hands you the choice. Once you have it, your accountant can run the numbers both ways and use whichever result is lower. Skip it, and that choice is made for you.
Example figures are illustrative only and will vary based on your own purchase price, growth pattern, and holding period. This article is general information, not tax advice. Speak with a registered tax agent or accountant about your own circumstances.
