Granny Flat ROI Calculator.
Calculate the return on investment from building a granny flat. See construction costs, rental income, and how long until it pays for itself.
Move the sliders or type your numbers in — the math updates live as you go. Click Get AI verdict when you want a written analysis.
Granny flats are one of Australia's best-kept property investment secrets — for $120,000-$200,000, you can add $300-$600/week in rental income with payback periods of 5-8 years. In NSW, complying development allows approval in as little as 10 days (no DA required). A granny flat also adds $100,000-$200,000 to your property's resale value. The key is getting the numbers right: council fees ($5,000-$15,000), connection costs ($10,000-$20,000), and ongoing expenses can erode returns if not planned properly.
Real-world scenarios
2-Bed Granny Flat — Western Sydney
Build cost: $160K. Rent: $450/week. Main house value: $850K. Financed from home equity at 6.2%.
Annual rent: $23,400. Annual expenses (insurance, maintenance, rates): ~$3,000. Equity interest: ~$9,920. Net annual income: ~$10,480. Payback period: ~7.6 years (cash) or ~15.3 years (after interest). Property value increase: ~$120K-$160K, meaning instant equity gain even before rental returns.