The CGT main residence "first used to produce income" rule: when renting out a room or running a home business changes your home's tax status

For Australian retirees considering supplementary income from their home — taking in a boarder, listing a spare bedroom on Airbnb, renting out a self-contained granny flat at the property, or running a late-career consulting practice from a home office — the CGT main residence exemption picture changes. The full main residence exemption that ordinarily protects the family home from capital gains tax on disposal applies only while the property is genuinely the owner's main residence and not used for income production. When part of the property begins to be used to produce income, section 118-192 of the Income Tax Assessment Act 1997 (https://classic.austlii.edu.au/au/legis/cth/consol_act/itaa1997240/s118.192.html, accessed 11 May 2026) triggers a specific cost base reset, and sections 118-185 and 118-190 (https://classic.austlii.edu.au/au/legis/cth/consol_act/itaa1997240/s118.185.html and https://classic.austlii.edu.au/au/legis/cth/consol_act/itaa1997240/s118.190.html, both accessed 11 May 2026) apply the apportionment framework that determines the eventual CGT consequences on sale. Understanding the rule is important for retirees considering home-based income arrangements — the cost base reset is generally favourable, capturing pre-rental capital growth as exempt, but the apportionment going forward creates ongoing tax exposure that accumulates over years of income use (ATO — using your home to produce income, https://www.ato.gov.au/individuals-and-families/investments-and-assets/capital-gains-tax/property-and-capital-gains-tax/your-main-residence-home/using-your-home-to-produce-income, accessed 11 May 2026).

The basic mechanism of s.118-192 is that when the property was the taxpayer's main residence and is first used to produce income at a later date (not at the time of acquisition), the taxpayer is treated as having acquired the dwelling at its market value at the time it is first used for that purpose. The cost base for CGT purposes is reset to that market value, and the dwelling is treated as acquired on that day. The reset effectively captures all the capital growth from the date of original acquisition to the date of first income use as exempt under the main residence framework — only post-reset growth on the income-producing portion is potentially subject to CGT on eventual sale. For a property purchased in 2010 for $600,000 and first used to produce income in 2025 when worth $1,500,000, the cost base for CGT purposes from 2025 onwards is $1,500,000 rather than the original $600,000. The 15 years of capital growth between 2010 and 2025 is captured as exempt under the main residence rules.

The rule applies where specific conditions in s.118-192(1) are met. The dwelling must have been acquired after 20 August 1996 (different transitional rules apply for pre-1996 acquired properties). The dwelling must have been the taxpayer's main residence and not previously used to produce assessable income. The first income use must occur at a time after acquisition. And the taxpayer must be entitled only to a partial main residence exemption under s.118-185 because the dwelling was used to produce assessable income during the ownership period. For most retirees considering home-based income production after years of pure main residence use, the conditions are satisfied and the rule applies automatically — there's no election to make; it operates as a deemed acquisition.

The apportionment of the eventual capital gain under sections 118-185 and 118-190 combines floor area and time methodologies. Section 118-190 provides the floor-area component — calculating the proportion of the dwelling's floor area that was used to produce assessable income. Section 118-185 provides the days-of-use component — the number of days during the ownership period in which the dwelling was used to produce assessable income, divided by the total ownership days. The combined apportionment produces the taxable portion of the post-reset capital gain. For a property where 30% of the floor area is income-producing and the income use occurs over 5 of the 15 years post-reset ownership, the taxable proportion would be roughly 30% × (5 × 365 / 15 × 365) = 10% of the post-reset gain. The 50% CGT discount typically applies to the taxable portion (where the asset has been held for more than 12 months), reducing the effective tax further.

Common income-use scenarios for retirees include a range of arrangements that all trigger the rule. Renting out a spare room to a boarder for ongoing income — once the income arrangement begins, s.118-192 applies. Listing on Airbnb the property or a portion of it — even occasional short-stay hosting triggers the rule, with the apportionment reflecting the actual hosting time and area. Running a home-based business with a dedicated home office — where the office is exclusively used for business (not also a study or spare bedroom), s.118-192 applies with the office floor area as the income-producing portion. Renting a self-contained granny flat at the property to a third party at market rent triggers the rule with the granny flat floor area as the income-producing portion. Each of these is a typical retirement-era arrangement that retirees should understand has CGT consequences.

A specific distinction worth flagging is the difference between a commercial granny flat rental (which triggers s.118-192) and a formal granny flat interest under the targeted CGT exemption that has applied since 1 July 2021 (ATO — granny flat arrangements and CGT, https://www.ato.gov.au/individuals-and-families/investments-and-assets/capital-gains-tax/exemptions-and-rollovers/granny-flat-arrangements-and-cgt, accessed 11 May 2026). A formal granny flat interest is a written arrangement under which an older or disabled person has the right to occupy a property for life, typically established between an elderly parent and their adult children, and meeting the eligibility conditions for the targeted CGT exemption. Where the conditions are met, the creation, variation, and termination of the granny flat interest is disregarded for CGT purposes, addressing the previous tax barrier to formalising these family arrangements. The CGT implications differ materially from a granny flat rented commercially to an unrelated tenant. For families considering granny flat arrangements, the structure of the agreement (formal granny flat interest under the post-1 July 2021 framework versus commercial rental) has CGT implications alongside the Centrelink and family-relationship considerations.

The home office for consulting scenario is increasingly common as retirees take on consulting work from home. The CGT trigger depends on whether the office is exclusively used for income production. Where a retiree dedicates a specific room as a consulting office (not used for personal purposes), the room qualifies as income-producing under s.118-192. Where a retiree uses a study that's also a personal study or guest bedroom (mixed use), the home office deduction calculation on the income tax side typically uses an hours-based method, and the CGT trigger generally does not apply because the room is not "set aside" for income-producing purposes. The trade-off between maximising the home office tax deduction (favouring exclusive use) and avoiding the CGT trigger (favouring mixed use) is a real planning consideration for late-career consultants.

For retirees who have already triggered the rule through ongoing income-producing use, the documentation discipline matters substantially. The records that need to be maintained include: the date of first income use (the trigger event), the market valuation at that date (independent valuation is strongly preferred over later reconstruction), the floor area of the income-producing portion, the days/time of income production each year, and any cessation periods. For a property that may be sold 10 to 20 years after income use begins, the records need continuous maintenance throughout. Without proper records, the ATO defaults can produce worse outcomes than proper apportionment would.

For sale planning, retirees with historical income use can take steps to reduce the CGT exposure. Ceasing income use well before sale (months to years) reduces the time apportionment under s.118-185 — if the property reverts to pure main residence for a meaningful period before sale, the apportionment of the post-reset gain reflects only the days of actual income use rather than the entire post-reset ownership. Documenting the cessation and any restoration to full main residence use supports the calculation. For some retirees, the small CGT cost of accumulated apportionment is worth accepting in exchange for the rental income generated; for others, the CGT cost is material and warrants planning around timing of cessation and sale.

The practical advice work for retirees considering home-based income production has a specific shape. Before commencing income use, model the projected CGT exposure over the expected period of income use and the expected eventual sale. Obtain market valuation at the start of income use — independent valuation is the right standard, with reports retained as part of the property records. Maintain records of dates, floor areas, income amounts, and any cessation periods. Review periodically as the income use evolves (more or fewer rooms rented, ceased Airbnb after a few years, etc.) and update records accordingly. Plan eventual sale considering the accumulated taxable portion and any CGT mitigation through ceasing income use before sale. Coordinate with broader tax planning — the income tax position on rental income, the deductions for property expenses during income use under the apportionment in s.118-190, and the CGT position on eventual sale all interconnect.

What do worked planning examples show?

These two cases show how the rule plays out for typical retiree home-income scenarios. Illustrative only — not personal advice — using FY25-26 figures.

Case 1 — Patricia, 71, considering taking in a boarder for $400 a week starting 1 July 2025. Her home was purchased in 2010 for $750,000 and is currently valued at $1,800,000. On these facts, s.118-192 applies on first income use. The dwelling is treated as acquired at $1,800,000 market value at 1 July 2025. The boarder will occupy 1 bedroom representing approximately 15% of floor area. If Patricia continues the arrangement for 10 years (to 2035) and sells at an assumed value of $2,400,000, the post-reset gain is $600,000. The taxable portion is roughly 15% × (10 / 10 years) × $600,000 = $90,000, with the 50% CGT discount producing an assessable $45,000. At Patricia's expected retirement-era marginal rate (approximately 19% in the post-tax-free-threshold band with SAPTO benefits), the CGT cost is approximately $8,500. Net rental income over 10 years (at $400/week × 50 weeks = $20,000/year, less property expense apportionment and tax) might be in the order of $130,000 to $150,000. The arrangement is net-favourable but the CGT cost is real and should be factored into the decision. The trap to avoid is starting the boarder arrangement without obtaining a market valuation at 1 July 2025 — the valuation is the foundation of the s.118-192 deemed acquisition cost base, and missing it makes the eventual CGT calculation harder and potentially more costly.

Case 2 — David, 67, has been renting his self-contained granny flat on Airbnb since 2022 (3 years). Property purchased 2008 for $400,000, currently valued at $1,400,000, granny flat is approximately 25% of total floor area. On these facts, s.118-192 applied at the start of Airbnb hosting in 2022 — David is treated as having acquired the dwelling at market value as at the first hosting day (assume $1,250,000). Three years of hosting have accumulated an apportioned taxable position under ss.118-185 and 118-190. If David sells in another 5 years (8 years post-reset) at an assumed value of $1,700,000, the post-reset gain is $450,000. The taxable portion, assuming continuous hosting, is approximately 25% × (8 / 8 years) × $450,000 = $112,500, with the 50% discount producing $56,250 assessable. CGT cost at his retirement marginal rate would be in the order of $10,000–$15,000. The total cost over 8 years of Airbnb income is real but small relative to the rental income generated. The trap to avoid is failing to record the 2022 market value — without that figure, David's CGT calculation defaults to less favourable methods. Obtaining a back-dated independent valuation now for the 2022 trigger date is valuable for the eventual sale.

For Australian retirees considering home-based income production through boarders, Airbnb, granny flat rentals, or home office business use, the s.118-192 cost base reset is the structural feature that determines the long-term CGT consequences. The reset is generally favourable — capturing pre-rental capital growth as exempt — but the post-reset apportionment under ss.118-185 and 118-190 creates ongoing tax exposure that accumulates over the years of income use. The practical advice work is to surface the rule before commencing income use, obtain a market valuation at the trigger date, maintain proper records throughout, and plan eventual sale considering accumulated apportionment. For most retirees, the after-tax economics of home income production work, but the CGT consequences are part of the decision and shouldn't be invisible.

Sources

• classic.austlii.edu.au — S118.192
• classic.austlii.edu.au — S118.190
• classic.austlii.edu.au — S118.185
• Australian Taxation Office (ATO) — Using your home to produce income
• Australian Taxation Office (ATO) — Granny flat arrangements and cgt