Granny flat investment in Australia: the 15% yield math nobody talks about

A standalone investment property in Sydney or Melbourne yields about 3% gross. A granny flat built on land you already own yields about 15%. That isn't a typo, and it isn't a sales pitch. It's arithmetic: a $150,000 build letting at $450 a week brings in $23,400 a year, which is 15.6% of the build cost. No land purchase, no stamp duty, no new mortgage on the dirt underneath.

The catch is that the math is the easy part. Planning consent, depreciation, capital gains tax, and the way lenders treat the rent are all messier than the headline yield suggests.

Why the yield is so high (and what it really means)

The reason a granny flat looks so good on paper is that the most expensive input in any Australian property purchase is the land. You already own it. Adding a second dwelling layers a new income stream onto a sunk cost. Compare that to buying a whole investment property where 60-70% of the purchase price is land you have to finance, insure, and pay rates on twice.

Counter-intuitively, the best granny-flat lots aren't in prestige suburbs. They're in the cheapest suburbs where rent-to-build ratios stay strong. A $150k build in Mount Druitt rents for roughly the same weekly figure as a $150k build in Mosman, because granny-flat tenants pay for shelter and location-within-a-region rather than postcode prestige. The expensive suburb just means a higher opportunity cost on the backyard.

State-by-state planning treatment

NSW is the easiest. The State Environmental Planning Policy (Affordable Rental Housing) 2009 lets most lots of 450m² or more put up a secondary dwelling under complying development, which means a private certifier signs it off in roughly 20 business days without going through council. Maximum 60m² of habitable floor area. Owner-occupier or investor, doesn't matter.

Victoria liberalised in 2024. Small second dwellings (under 60m²) on existing residential lots no longer need a planning permit in most zones, only a building permit. Some Design and Development Overlays still apply, and councils retain discretion on heritage overlays and bushfire-prone land, so the path is faster than it was but not as clean as NSW complying development.

Queensland is the trap. Most councils permit a secondary dwelling under the term "auxiliary unit" or "dependent person's accommodation", but the rental restrictions vary council by council. Brisbane City Council allows rental to non-family members. Some regional councils restrict occupancy to a dependent relative, which kills the investment thesis entirely. Check the local planning scheme before signing a builder's contract, not after.

The worked example: $160k build in Western Sydney

Take a real-world setup. Existing house in Penrith. Backyard with 200m² of clear space. Two-bedroom granny flat under complying development, built at $160,000 turnkey including site costs, connections, and a small concrete driveway.

• Build cost: $160,000
• Weekly rent: $470 (two-bedroom, separate entrance, off-street parking)
• Annual gross rent:$470 × 52 = $24,440
• Gross yield: $24,440 / $160,000 = 15.3%
• Operating costs: council rates uplift $800, landlord insurance $700, maintenance/sinking allowance $1,500, water $300, property management 7% = $1,710. Total roughly $5,000.
• Net cash yield:($24,440 − $5,000) / $160,000 = 12.2%
• Simple payback: roughly 8.2 years on net cash, ignoring tax effects.

The rental yield calculator will run the same arithmetic on your own build cost and rent estimate. Sanity-check both inputs before committing: builders quote optimistically, and rental appraisals come in higher than what the property actually lets for once vacancy is real.

Depreciation: where the after-tax return gets interesting

A brand-new granny flat is one of the most depreciable assets in the residential property tax code. The structure itself (Division 43 capital works) is deductible at 2.5% of build cost per year over 40 years, so a $160k build delivers $4,000 a year on the structure alone. Plant and equipment (Division 40: ovens, dishwashers, air-con units, blinds, carpets) front-loads heavier deductions into the first five years, often $2,000 to $3,000 a year before tapering.

Combined Div 43 and Div 40 deductions in years one through five typically run $5,000 to $7,000 a year on a build of this size. At a 37% marginal tax rate, that's roughly $2,000 of additional cash back per year, lifting the after-tax cash yield closer to 13-14%. The depreciation schedule walkthrough explains why getting a quantity surveyor's report in year one is non-negotiable for a new build. The fee (around $700) pays for itself in the first quarter's tax return.

The CGT trap most owners miss

Your main residence is normally exempt from capital gains tax on sale. The moment you rent out a portion of the same lot, that exemption gets prorated. The ATO uses two ratios: floor area let versus total floor area, and time let versus total ownership period. A 60m² granny flat on a property with a 180m² main house represents 25% of total floor area. Rent it out for ten years on a thirty-year hold and roughly 25% of ten-thirtieths (about 8%) of the eventual capital gain becomes taxable.

On a property that appreciates from $800k to $1.4 million over thirty years, that's about $48,000 of assessable gain at sale. The 50% CGT discount halves it to $24,000, and at a 37% marginal rate that's a tax bill near $9,000. Not catastrophic, but real, and easy to forget when the cash yield is humming along at 13%.

Get an adviser to model your specific ratios before building. The numbers shift materially if the granny flat is built earlier in the ownership period, if the main residence is later converted to a rental, or if a six-year absence rule comes into play. None of this kills the investment thesis, but it does mean the after-tax IRR over a long hold is a couple of points lower than the headline yield suggests.

The financing reality

Most banks will lend against a granny flat, but the serviceability assessment is uneven. Lenders typically count only 80% of the expected granny-flat rent toward your servicing capacity, which is the same haircut they apply to standard rental income. A few smaller lenders apply a heavier discount or refuse to count the income at all if the secondary dwelling can't be subdivided and sold separately (which under NSW SEPP rules, it can't).

The most common funding routes are a construction loan bolted onto an existing mortgage (a top-up redraw against accumulated equity), or a personal loan or line of credit for the build with refinance into a single home loan once the certificate of occupancy lands. The borrowing power calculator can model what an extra $24k of gross rent (counted at 80%) does to your capacity, which is useful if the next move is a third property purchase.

Land tax aggregation in NSW and VIC

A granny flat on its own doesn't trigger land tax, because the land tax thresholds in both NSW ($1.075 million in 2026) and VIC ($300,000) apply to total taxable land holdings across all properties. The granny flat's marginal land value is zero in the eyes of the assessor, since the lot was already owned.

The aggregation matters once you have multiple properties. Two investment properties plus a primary residence with a granny flat can push total taxable holdings above the threshold, and once you're over, the rate climbs fast. VIC's threshold is particularly punishing because $300,000 of unimproved land value is easy to clear with a single inner-suburb investment property. Model it on the whole portfolio, not the new project in isolation.

How it stacks up against other investment options

A granny flat does one thing better than almost any other residential property play: it produces high cash yield from day one. The trade-off is that capital growth on the granny flat itself is negligible. It's a depreciating asset sitting on appreciating land you already owned. The land keeps doing what land does. The structure quietly loses value.

That makes it a different category of investment to a standalone rental purchase, which the property vs shares comparison treats as a leveraged growth play. A granny flat is closer to a high-yield bond paid in rent. If the rest of your portfolio is heavy on capital growth bets (negatively-geared units, an SMSF property), the granny flat's cash flow is a useful counterweight that pays the holding costs on everything else. The negative gearing piece gets into how those interactions work at the portfolio level.

The honest verdict

For someone who already owns a suitable lot in a state with rental-friendly planning rules, a granny flat is one of the few residential investments where the cash math actually works without leverage games and growth assumptions. A 12-13% net cash yield after operating costs is real, repeatable, and verifiable before you sign a builder's contract.

The arguments against are smaller than they look: the CGT prorate is a couple of points off long-run IRR, not a deal- breaker. The lender haircut on rental income is the same haircut applied everywhere else. Planning consent in NSW and VIC is straightforward. QLD requires a council check before the cheque clears.

Run your own numbers, not the brochure's. Use realistic rent (the bottom of the range your agent quotes, not the top), realistic build cost (add 10% for site costs the quote-stage didn't catch), and realistic vacancy (two weeks a year is fair). If the yield still comes in above 11% net cash, the project has structural margin. If it's below 9%, the numbers are too tight to absorb a tradesman's bad week.