Granny Flat ROI Calculator
AI + Live DataCalculate the return on investment from building a granny flat. See construction costs, rental income, and how long until it pays for itself.
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.
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Real-World Examples
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.
Frequently Asked Questions
Glossary
How to Use
- 1Enter the estimated total build cost (construction + council + connections).
- 2Set the expected weekly rent for the granny flat.
- 3Add your main property's current value.
- 4Choose the granny flat size and your state.
- 5Select the purpose and financing method.
- 6See payback period, ROI, and impact on total property value.
Key Information
- Average granny flat build cost: $120K-$200K (1-2 bed, including council and connections).
- Average granny flat rental income: $300-$600/week depending on location and size.
- Typical payback period: 5-8 years for long-term rental, 3-5 years for Airbnb (where permitted).
- NSW allows up to 60sqm complying development granny flats with 10-day CDC approval.
- Granny flat rental income is taxable but expenses (construction depreciation, insurance, rates portion) are deductible.
Pro Tips
- In NSW, use a Complying Development Certificate (CDC) instead of a DA — it's faster (10 days vs months) and more predictable.
- Build to the maximum size allowed — the rental premium for a 2-bed over a 1-bed far exceeds the extra construction cost.
- Fund from home equity (redraw) at your home loan rate — much cheaper than a separate construction loan.
- If considering Airbnb, check your council's short-term rental rules — many LGAs now cap it at 180 days/year.
Avoid These Mistakes
- Underestimating connection costs — sewer, water, electricity, and stormwater connections can add $10K-$20K.
- Not checking council rules before committing — minimum lot sizes, setbacks, and parking requirements vary by council.
- Building cheap to save money — poor quality builds cost more in maintenance and attract lower rents.
- Forgetting that the granny flat can't be strata-titled in most states — you can't sell it separately from the main house.
Disclaimer: This calculator provides estimates only and should not be relied upon for financial decisions. Interest rates, fees, and policies change frequently. Always verify information with lenders directly. This is general information, not personal financial advice. Consider seeking advice from a licensed mortgage broker or financial advisor.
Last updated: February 2026