Granny Flat Tax Deductions
Understand what you can and can't deduct when renting out a granny flat or secondary dwelling on your property.
What is a Granny Flat for Tax Purposes?
A granny flat is a self-contained dwelling on the same land title as your main residence, typically including:
- Separate bedroom, bathroom, and kitchen facilities
- Independent access (separate entrance)
- Located at the rear or side of the main dwelling
When you rent out a granny flat while living in the main residence, you create a mixed-use property with both rental income and tax implications.
What You Can Deduct
Expenses Directly Related to the Granny Flat & it's rental income
You can claim 100% of expenses exclusively related to the granny flat:
- Repairs and maintenance: Fixing plumbing, painting, appliance repairs specific to the granny flat
- Depreciation: Building structure (2.5% per year if constructed post-1987) and plant/equipment (appliances, carpets, blinds)
- Insurance: If you have separate insurance for the granny flat or a compoennt that relates to landlord insurance
- Utilities: If the granny flat has separate meters (not recovered from tenant)
- Cleaning and gardening: If exclusively servicing the granny flat area
- Property management and admin: If you use a property manager or Mint Property Mate, you can apportion the fee based on granny flat floor area
- Advertising and inspection costs: If you advertise the granny flat or conduct inspections, these are 100% deductible.
Apportioned Shared Expenses
For expenses that benefit both the main residence and granny flat, you must apportion based on floor area:
- Council rates: Apportion based on granny flat's proportion of total land and building area
- Land tax: Same apportionment as council rates
- Insurance: If a single policy covers both dwellings, apportion the premium
- Water and sewerage charges: Must be apportioned based on floor area (not occupant numbers). The ATO doesn't accept per-person apportionment even if the granny flat has fewer occupants than the main house
- Gardening and lawn care: If servicing shared grounds
Deductible amount = Total expense × (Granny flat floor area ÷ Total property floor area)
Example: Granny flat is 60m², main residence is 240m², total 300m².
Apportionment: 60 ÷ 300 = 20%
If council rates are $3,000, you can deduct $600.
Use this quick calculator to determine your deductible portion:
Mortgage Interest – Apportioned by Loan Drawdown
Mortgage interest requires a different apportionment method. Interest is deductible only on the portion of the loan funds that were actually used to construct or improve the granny flat—not based on floor area.
Example: You've taken out a $500,000 loan secured against your property. However, only $100,000 of that loan was specifically used to build/extend the granny flat. In this case, you can claim interest on the $100,000 portion (20% of total), not 20% based on floor area.
If you used the loan for multiple purposes (general home improvement, granny flat construction, debt consolidation), you must track which funds were drawdown for the granny flat to determine the deductible interest portion.
What You Cannot Deduct
- Mortgage principal: Only interest (and only if the loan funded the granny flat) is deductible
- Initial construction costs: These are capital expenses depreciated over time, not immediately deductible
- Expenses for the main residence: Repairs, improvements, or maintenance exclusively benefiting your home are not deductible
- Personal living expenses: Your own utilities, groceries, or personal costs
Capital Gains Tax Implications
Renting out a granny flat has significant CGT consequences. This topic is covered in detail in our separate CGT article. In summary: your main residence is normally CGT-exempt, but renting out a granny flat creates a partial CGT liability when you eventually sell.
Depreciation for Granny Flats
Granny flats can generate significant depreciation deductions:
Capital Works Deduction (Division 43)
- 2.5% per year of construction cost for 40 years
- Requires construction to have occurred after 15 September 1987
- Claim 100% of granny flat construction cost (no apportionment)
Plant and Equipment (Division 40)
- Appliances, carpets, blinds, air conditioners installed in the granny flat
- Depreciate at various rates depending on effective life
Record Keeping
The ATO requires landlords to keep detailed records for 5 years:
- Rental income records (bank statements, rental ledger)
- Receipts for all expenses (repairs, rates, insurance)
- Floor area calculations and apportionment methodology
- Construction invoices and costs
- Depreciation schedule
- Photos of the granny flat and property layout
Common Mistakes to Avoid
- Claiming 100% of shared expenses: You must apportion council rates, land tax, and other shared costs.
- Ignoring CGT implications: Selling your home will trigger a partial CGT liability – plan accordingly.
- Not obtaining a depreciation schedule: Missing out on thousands in deductions.
- Incorrect apportionment: Using arbitrary percentages instead of floor area calculations.
- Claiming main residence expenses: Only granny flat expenses are deductible.
Mint's Takeaway
- Expenses directly related to the granny flat (repairs, depreciation) are 100% deductible.
- Shared expenses (rates, insurance) must be apportioned based on floor area.
- Capital works deduction: 2.5% per year of granny flat construction cost.
- Renting out a granny flat creates a partial CGT liability when you sell – calculate this impact early.
- Obtain a quantity surveyor's depreciation schedule to maximize deductions.
- Keep detailed records of all expenses, income, and apportionment calculations.
- Consult a tax professional to ensure compliance and optimize your tax position.
Mint simplifies granny flat expense tracking with automatic apportionment and depreciation calculations.