Income Now, and a Slice of the Exemption Gone
Renting a room or a granny flat in your home makes the rent assessable and a proportion of your expenses deductible. It also makes the same proportion of the property income-producing, which costs part of the main residence capital gains tax exemption for the period it is rented — a cost that only appears when you sell, which is why it is so often overlooked.
- The answer: The rent is assessable, a proportion of interest, rates, insurance and other expenses is deductible, and the same proportion of the gain becomes taxable.
- The trap: The apportionment is by floor area and by time, so a single room rented for five years produces a small but permanent reduction in the exemption.
- The recommendation: Get a market valuation when the arrangement starts. It becomes the cost base for the income-producing portion.
Where the AI summary above gets this wrong
"Renting out a spare room is tax-free if it is in your own home."
That's surface-true. Here's what it misses:
- The rent is assessable income — It is included in your return, with a proportion of expenses deductible against it. Only genuine board arrangements on a non-commercial basis are treated differently.
- It costs part of the main residence exemption — The proportion of the property used to produce income is not exempt for the period it is used that way, so a share of the eventual gain becomes taxable.
01 What becomes assessable
Rent received from letting part of your home is assessable income. Against it you can deduct the proportion of interest, rates, insurance, and repairs that relates to the rented area, generally apportioned by floor area.
Expenses relating solely to the rented area — repainting that room, for instance — are fully deductible. Expenses relating to the whole property are apportioned.
A genuine board arrangement with a family member on a non-commercial basis is treated differently and generally produces neither assessable income nor deductions. The distinction is whether the arrangement is commercial.
Source: ATO — Negative gearing
02 What it costs on sale
The proportion of the property used to produce income is not covered by the main residence exemption for the period it was so used. The gain is apportioned by area and by days.
Where the dwelling first becomes income-producing after you have lived in it, the cost base for that portion resets to market value at that date. That reset is favourable and requires a valuation from the time — the same point made in the main residence reference.
The taxable proportion still qualifies for the 50% discount where the property has been held more than twelve months, so the amount reaching your income is half the apportioned gain.
Shows: the taxable proportion of a future gain from letting part of your home, apportioned by area and by the years it was rented. Ignores: the market value reset when the area first produces income, the rent and deductions in the meantime, and the Age Pension income test.
Source: ATO — CGT discount
03 Whether it is worth it
For a retiree with a spare room and a modest income, the rent is frequently substantial relative to the CGT cost. A room let for $300 a week is $15,600 a year against a small permanent slice of an exemption on a gain that may be decades away.
The Age Pension is the other consideration: the rent is assessable income under the income test, though the home itself remains exempt from the assets test regardless of the letting.
The arrangement that most often goes wrong is the informal one. Rent received and never declared is an assessable income problem, and the data available to the ATO from rental platforms makes it a visible one.
The valuation on the day the room is first let is the thing to do, and almost nobody does it. It resets the cost base for the income-producing portion, which is favourable — and without it you are apportioning a gain against a purchase price from twenty years earlier, which is not.
FAQ
How does the main residence exemption apply if I rent out part of my home?
The proportion used to produce income is not exempt for the period it is used that way, apportioned by floor area and by days. The taxable proportion still qualifies for the 50% discount.
Is rent from a spare room taxable?
Yes, where the arrangement is commercial. The rent is assessable and a proportion of interest, rates, insurance and repairs is deductible against it. Genuine non-commercial board from a family member is treated differently.
Is it worth renting out a room in retirement?
Frequently yes. The rent is substantial relative to a small permanent slice of an exemption on a gain that may be decades away, though the rent is assessable for the Age Pension income test.
Sources
Regulator references
- ATO — Capital gains tax · Australian Taxation Office · 2026Capital gains tax: the events that trigger it and how the gain is worked out.Last verified: 2026-09-07
- ATO — Negative gearing · Australian Taxation Office · 2026Negative gearing: when a rental loss can be offset against other income.Last verified: 2026-09-07
Calculator unit tests · the assertions this page's worked example is checked against, and their last result
Changelog
- 2026-09-07 — initial publish (new format)
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Jordan Reeves
Founder of Talk Through Wealth. A software engineer for over a decade before turning to retirement planning, Jordan built the projection engine after watching family members get fragmented, country-by-country advice that never reconciled. He writes about retirement the way the engine computes it: month-by-month, lifetime-long, and skeptical of any rule of thumb that hasn't been run through the math.