About GrannyFlatCost
GrannyFlatCost is a free, independent cost calculator that helps Australian homeowners understand the true cost of building a granny flat â before they talk to a single builder.
Why we built this
When you search "how much does a granny flat cost," you get vague ranges ($100kâ$300k) and builder websites that want your phone number before showing prices. We think you deserve real numbers upfront.
We analysed pricing data from over 10 Australian granny flat builders, compiled state government fee schedules for all 8 states and territories, and built a calculator that gives you a personalised estimate in under 2 minutes.
How we're different
- No builders pay to be listed. Our estimates are independent and not influenced by any builder relationship.
- Real data, not guesses. Every cost figure is derived from published builder prices, state fee schedules, and industry reports.
- State-specific. Regulations, approval pathways, and costs vary dramatically by state. Our calculator accounts for this.
- Free, no signup required. Use the calculator as many times as you want. We'll only ask for your details if you want a detailed report sent to you.
Our methodology
We use a component-based cost model that breaks the total project cost into five categories: base build, site preparation, utility connections, design and approvals, and contingency. Each component is calculated using multipliers derived from real market data.
Read our full methodology or see our data sources.
Important disclaimer
Our estimates are indicative only and based on publicly available data. Actual costs will vary based on your specific site conditions, council requirements, builder choice, and market conditions. Always obtain multiple quotes from licensed builders before committing to a project.