The CGT main residence exemption, and 6 traps that catch otherwise careful sellers
The capital gains tax main-residence exemption seems straightforward. Six edge cases catch out sellers every year. Each one can convert a tax-free sale into a five or six-figure tax bill.
The main residence exemption is one of the most generous tax provisions available to Australian property owners. Your principal place of residence (PPOR) is exempt from capital gains tax when you sell, provided you have lived in it and have not nominated another property as your PPOR for the same period.
The exemption sounds simple. The application is not. Six common situations strip the exemption partially or entirely, and most sellers do not know until their accountant tells them at tax time, by which point the calculation is fixed.
Here are the six traps and how to avoid each.
Trap 1: The 6-year absence rule
If you move out of your PPOR and rent it, you can continue to treat it as your PPOR for up to 6 years, provided you do not nominate another property as your PPOR in that period.
Trap: you nominate a new property as your PPOR (perhaps the one you moved into). The original property's CGT exemption stops accruing from that moment. The gain attributable to the period after the nomination is taxable.
Avoid: keep careful records of which property is your nominated PPOR at each point in time. The ATO allows one nomination at a time. If you own both, choosing wisely between them at sale matters.
Trap 2: The 6-month overlap rule
When you buy a new home and sell the old one, there is a 6-month overlap window during which both can be treated as your PPOR. After 6 months, you must nominate.
Trap: the sale of the old property takes longer than 6 months (the contracts crossed, then settlement slipped, then a buyer walked). You exceed the 6-month window. Now one of the two is taxable for the overlap period.
Avoid: aim to settle the sale within 6 months of moving into the new place. If you cannot, document the reasons. The ATO is occasionally lenient on genuine delays. Not always.
Trap 3: The home office / running-a-business-from-home rule
If you have used part of your home to run a business (not just claimed work-from-home expenses), the business-use portion of the property can be subject to CGT proportionate to its area and time of business use.
Trap: a doctor who saw patients from a converted ground-floor room for 8 years. A consultant who claimed a dedicated office for 12 years. The CGT applies to roughly the floor area of the business use times the proportion of ownership it was used that way.
Avoid: distinguish between "working from home" (no CGT impact) and "running a business from home" (CGT impact). The ATO test is whether the area is a "place of business" with the character of a business: signage, dedicated entry, client visits, exclusive use.
Trap 4: The apportionment rule for property used to produce income
If part of the property is rented (e.g. a separate granny flat, a Airbnb room with its own entrance), the rented portion is not part of the main residence exemption.
Trap: a homeowner converts the garage into a self-contained studio and rents it for 4 years. At sale, the studio's pro-rated capital gain is taxable.
Avoid: be careful with secondary dwellings. If you rent any part of the property to a third party, the area-based exemption splits. A granny flat with a separate kitchen, bathroom, and entry is the canonical example. A shared bedroom in the main house is more ambiguous.
Trap 5: The "main residence" definition trap
To qualify as a main residence, you must actually live in the property. Briefly moving in to claim the exemption does not work. The ATO looks at:
- How long you lived there
- Whether you slept there
- Whether your mail was directed there
- Whether your bills were registered there
- Whether you were genuinely settled
Trap: a developer who builds, briefly lives in, and sells within 12 months. The ATO may treat the property as inventory of a property-development business rather than a main residence, applying both CGT and possibly income tax.
Avoid: establish actual residence. Not just on paper. Several months of genuine living, with bills and mail and routine, is the minimum for an arguable case.
Trap 6: The pre-CGT cost base reset on death
When a property owner dies, the cost base of the main residence resets to its market value at death for inheritors. If the inheritor then sells the property as a non-main-residence (because they have their own PPOR), the gain is calculated from the date-of-death value, not the original purchase price.
Trap: a parent's home, bought for $80,000 in 1985, worth $1.4M at their death in 2026. The child inherits and sells for $1.5M six months later. If the child does not move into the property and does not nominate it as their PPOR, the CGT applies to the $100k gain (from $1.4M to $1.5M), not the original $80k cost base.
This trap actually favours the inheritor in most cases. The cost-base reset removes 41 years of capital gain from the calculation. But sellers often assume the cost base is the original purchase price and get a pleasant surprise. Knowing about the reset is the difference between a tax bill assumed and a tax bill correct.
What to do about each
Three habits:
- Keep your records. Date you moved in. Date you moved out. Date you started or stopped renting. Date you started a home business. Receipts for improvements (which lift the cost base). The ATO requires records for at least 5 years after sale.
- Nominate explicitly when you own two properties at once. The default is usually fine, but in the 6-year-absence and 6-month-overlap scenarios, the explicit nomination is what your accountant will need.
- Get advice before sale, not after. A 20-minute call with your accountant before listing costs nothing and either confirms your assumption or saves you five figures of tax.
What SafeBuy does provide: a complete property history (when you bought, when you sold, what the comparable sales were doing) that your accountant can read directly into the CGT calculation. The data layer matters for the math. The math itself is your accountant's job.
The main residence exemption is the single most valuable tax provision available to most Australian homeowners. Knowing how to keep it is worth more than knowing how to compute it.
