Mortgage Interest Tax Deductions
Mortgage interest is often the largest single tax deduction for landlords. Learn what's deductible and how to optimize your claims.
What Mortgage Interest is Deductible?
Interest on loans used to purchase, refinance, or improve your rental property is fully tax deductible.
The key requirement is that the borrowed funds must be used for income-producing purposes – specifically, to earn rental income.
Annual interest: $30,000
Tax deduction: $30,000
Tax saved (at 37% marginal rate): $11,100
What You Can Deduct
- Interest on the original purchase loan: The primary mortgage used to buy the investment property
- Refinancing interest: Interest on loans used to refinance the original investment property loan
- Construction loan interest: Interest during construction of a new investment property
- Renovation loan interest: Interest on loans used to renovate or improve the rental property
- Line of credit interest: If the borrowed funds were used for rental property purposes
Mint's Rule of Thumb
Only interest is deductible – principal repayments are not. Your loan statement will separate these amounts.
What You Cannot Deduct
- Principal repayments: Only interest is deductible, not the loan principal being paid down
- Interest on your primary residence: Personal home loans are not deductible
- Interest on funds used for personal purposes: If you withdraw equity for personal use, that interest is not deductible
- Penalty interest and late fees: Generally not deductible unless incurred in earning rental income
Mixed-Use Loans: Apportionment Required
If your loan is used for both investment and personal purposes, you must apportion the interest deduction based on the investment portion.
- $400,000 used to purchase a rental property
- $200,000 used for personal spending
Total annual interest: $36,000
Investment portion: $400,000 ÷ $600,000 = 66.67%
Deductible interest: $36,000 × 66.67% = $24,000
Loan Establishment Fees / Borrowing Costs
One-time fees charged when you take out or refinance a loan:
- If under $100: Immediately deductible
- If $100 or more: Deducted over 5 years (or the loan term if shorter)
Annual deduction: $1,200 ÷ 5 = $240 per year for 5 years
Interest-Only vs Principal and Interest Loans
Interest-Only Loans
Advantages:
- Maximize tax deductions (100% of repayments are deductible interest)
- Improve cash flow for negatively geared properties
- Preserve capital for other investments
Disadvantages:
- Loan principal doesn't reduce (no equity build-up from repayments)
- Higher total interest paid over the loan life
- Eventually converts to principal and interest (higher repayments)
Principal and Interest Loans
Advantages:
- Reduces loan balance over time
- Lower total interest paid
- Builds equity faster
Disadvantages:
- Only interest portion is deductible (not principal repayments)
- Higher monthly repayments
Mint's Fresh Take
Many investors use interest-only loans for rental properties to maximize deductions, while using principal and interest loans for their own homes to pay them off faster. What's right for you will depend on your goals; if you want the property to be a regular passive income source it may be best to keep paying down the home loan. If you plan to sell in a few years and capital growth is high it could be best to do principal-only. It all depends on your goals and the market.
Record Keeping
To claim mortgage interest deductions, keep:
- Loan statements showing interest charged
- Records of how borrowed funds were used
- Evidence of apportionment for mixed-use loans
- Prepayment and establishment fee receipts
Records must be kept for 5 years from the date of lodgement.
Common Mistakes to Avoid
- Claiming principal repayments: Only interest is deductible, not the principal reduction.
- Mixed-use loans without apportionment: Claiming 100% of interest when the loan is partially personal.
- Claiming pre-rental interest: Interest before the property is available for rent is not deductible.
- Not separating personal and investment loans: Complicates deductions and invites ATO scrutiny.
Mint's Takeaway
- Mortgage interest is fully deductible if the loan is used to purchase, refinance, or improve an income-producing rental property.
- Only interest is deductible – principal repayments are not.
- Keep investment loans separate from personal loans to avoid apportionment complexity.
- Loan establishment fees over $100 are deducted over 5 years (or loan term if shorter).
- Interest-only loans maximize tax deductions but don't reduce the loan balance.
- When converting your home to a rental, only interest after conversion is deductible.
Mint helps you separate interest from principal payments and calculates your deductible interest.