Is a Granny Flat a Good Investment? How the Numbers Work
Building a granny flat is a significant financial decision, so it’s reasonable to ask: is a granny flat a good investment, or just an expensive addition to the property? For most Sydney homeowners, the answer comes down to one concept — positive gearing — and a handful of numbers worth understanding before you commit.
Here’s how to work out whether a granny flat makes financial sense for your property. (This is general information, not personal financial or tax advice — speak with your accountant or financial adviser about your own situation.)
What “Positively Geared” Actually Means
A property investment is positively geared when the rental income it earns is greater than the costs of holding it, mainly loan interest. In simple terms: if the rent coming in exceeds the interest going out, you’re ahead each year, even without factoring in any future capital growth.
This is the opposite of negative gearing, where holding costs exceed rental income and the investor is relying on long-term capital growth to come out ahead. You can read more about how gearing works from ASIC’s Moneysmart, an independent government resource on property investment.
Granny flats are a common example of a positively geared investment, because the land is usually already paid for — you’re only financing the construction cost, not an entire second property.
A Real Example: The Numbers on a 60m² Granny Flat
Numbers are more useful than general claims, so here’s a worked example based on a standard 60m² granny flat with one bathroom, built as a rental.
Estimated total project cost:
- Turn-key design, approval & construction package: $154,900
- Council Section 7.11 contributions: $9,000
- Main electrical board upgrade (if required): $2,500
- Landscaping & fencing: $3,500
- Total project cost: $169,900
Estimated annual return, assuming $500 per week in rent:
- Annual rental income: $26,000
- Interest payable on the total project cost (at 6% p.a., assuming 100% finance): approximately $10,194
- Additional gross income per year: approximately $15,806
- Return on investment (gross income ÷ total project cost): approximately 9.3% per annum
These figures are estimates only. Actual costs and returns will vary depending on your site, finance terms, and local rental market, and don’t account for expenses like agent fees, maintenance, insurance, or other outgoings. Still, the principle holds: because you’re financing construction rather than a full second property, a granny flat can generate meaningful rental income relative to what it costs to build.
See example floor plans used in this scenario.
Why Granny Flats Tend to Perform Well as Investments
A few factors work in a granny flat’s favour as a rental investment:
- No land purchase required. You’re building on land you already own, which dramatically lowers the entry cost compared to buying a second property.
- Strong, steady rental demand. Secondary dwellings are popular with singles, couples, and downsizers looking for independent living close to family or transport.
- Dual-income potential. Many homeowners rent out the main house or the granny flat (or both), effectively creating two income streams from one block of land.
Costs That Are Easy to Overlook
The headline construction price isn’t the full picture. Section 7.11 council contributions, any electrical upgrade needed to support a second dwelling, and basic landscaping and fencing can add meaningfully to the total project cost. A genuine fixed-price tender should account for all of this upfront, rather than surfacing as “extras” partway through the build.
Risks and Variables Worth Weighing
No investment is without risk, and a granny flat is no exception:
- Interest rate movements directly affect your holding costs and therefore your return.
- Vacancy periods between tenants reduce your actual rental income below the estimate.
- Construction delays can extend the time before the property starts earning rent at all.
- Maintenance and compliance costs continue after handover, not just during the build.
Understanding these variables upfront — rather than discovering them later — is what separates a well-planned investment from a risky one.
See how our structured design and approval process accounts for these variables.
How The Granny Flat Experts Reduces the Risk
A few safeguards specifically address the risks above. A Rental Guarantee reimburses you the equivalent rent for every week construction runs over the agreed timeframe, directly protecting the “vacancy before income” risk. A 7-year structural warranty (against a 6-year industry standard) and a 120-day maintenance period after handover (against a 90-day industry standard) help manage costs after the build is finished. And because every project starts with a free, fixed-price tender, you know the real total cost before committing — not an estimate that grows as the project progresses.
Frequently Asked Questions
Is the ROI example the same for every property?
No. The figures above are based on a standard 60m² granny flat and a specific rental and finance assumption. Your actual cost and return depend on your site, council contributions, finance terms, and local rental demand, which is why a fixed-price tender is based on an assessment of your specific property rather than a general estimate.
How is rental income from a granny flat taxed?
Rental income is generally taxable, and you may be able to claim deductions for things like interest, depreciation, and maintenance. Tax treatment depends on your personal circumstances, so this is worth discussing with your accountant or a qualified financial adviser rather than relying on general information.
Do I need a full deposit upfront to get started?
No. The process typically starts with a free, obligation-free site assessment and tender, so you can see the real numbers for your property before committing to anything.
Get Your Own Numbers
Every property is different, so the only way to know your actual return is to start with a free site assessment and a fixed-price tender specific to your block. At The Granny Flat Experts, that assessment is free and obligation-free, and for a limited time, new clients can also access $10,000 worth of upgrade inclusions for just $4,900 on a standard 60m² granny flat.
