When considering building a granny flat on your principal place of residence, it’s important to understand the potential tax implications. This article will explore the key tax consequences that homeowners should be aware of.

Tax Implications of a Granny Flat on a Principal Residence
Capital Gains Tax (CGT):

Normally, your principal place of residence is exempt from Capital Gains Tax (CGT). However, if you build a granny flat and generate rental income from it, a portion of your property may become subject to CGT when you sell.

The CGT calculation would typically consider the proportion of the property used for income-producing purposes and the length of time it was used in this way.

Rental Income Taxation:

Income earned from renting out a granny flat is considered taxable income. This means you must declare it in your annual tax return.

Expenses related to the granny flat, such as a portion of utility bills, maintenance, and depreciation, may be deductible against this rental income.

Goods and Services Tax (GST):

Generally, renting out a residential property is exempt from GST. However, if you’re considered to be carrying on an enterprise (like if you build multiple granny flats for commercial purposes), GST implications may arise.

Land Tax:

In some Australian states, land tax is payable on properties above a certain value, excluding the principal place of residence. Adding a granny flat could potentially increase the value of your property and may impact your land tax obligations.

Building and Construction Implications:

Building a granny flat could be considered a capital improvement, which may affect the property’s cost base for CGT purposes.

Possible CGT Discount:

If the granny flat has been used to generate income for more than 12 months, you may be eligible for a CGT discount (usually 50% for individuals) on the income-producing portion when you sell.

Council Rates and Insurance:

Building a granny flat may increase your council rates and home insurance premiums. These costs are not directly tax-related but are important financial considerations.

Negative Gearing:

If your expenses for the granny flat exceed the rental income, you may be able to claim negative gearing benefits, reducing your overall taxable income.

Stamp Duty and Other Fees:

Depending on your state or territory, additional costs such as stamp duty or development application fees might apply when building a granny flat.

Main Residence Exemption:

If the granny flat is occupied by a family member and not rented out, the main residence exemption for CGT may still fully apply, but this can be a complex area requiring professional advice.


Building a granny flat on your principal residence can have various tax implications, primarily related to CGT, rental income, and possible deductions. It’s crucial to get professional tax advice tailored to your specific situation, as the tax laws can be complex and vary based on individual circumstances and changes in legislation. Consult with us or the Australian Taxation Office (ATO) will provide clarity and help in making informed decisions.