It’s one of the most common questions property investors ask: should I pay interest-only or principal and interest on my investment loan? The answer isn’t the same for every investor, and the wrong choice can cost you — either in cash flow today or tax efficiency long-term.
Here’s how to think through it properly.
What You’re Actually Choosing Between
When you take an interest-only (IO) loan, your repayments cover only the interest charged each month. Your loan balance doesn’t reduce. When the IO period ends, you either roll to principal and interest, refinance, or renegotiate.
With principal and interest (P&I), every repayment chips away at your loan balance. You build equity faster, and you’ll pay less total interest over the life of the loan.
So on paper, P&I wins for total cost. But for investors, that’s not the only lens that matters.
The Cash Flow Argument for Interest-Only
On a $700,000 investment loan, the difference between IO and P&I repayments can be $800–$1,200 per month. That’s significant cash flow.
For a property investor, keeping repayments lower means:
- More capacity to hold property through vacancy, rate rises, or income disruption
- Retained liquidity for the next acquisition
- Less personal capital tied up in non-deductible debt reduction
If you have owner-occupied debt running in parallel — a home loan that isn’t tax-deductible — the logic is even stronger. Pay down your home loan first (P&I on the owner-occ), hold your investment loan on IO, and use the freed-up cash to accelerate your non-deductible debt. This is a basic principle of debt optimisation that many borrowers miss.
The Tax Deductibility Angle
Interest on investment loans is generally tax-deductible. Principal repayments are not. So when you make a P&I repayment on an investment loan, part of it (the principal) is reducing a deductible debt — with no tax benefit for doing so.
IO repayments are fully deductible. That’s not a reason to pay IO forever, but it is a legitimate factor in the decision, particularly for high-income earners in upper marginal tax brackets.
Speak to your accountant before making this decision. The right structure depends on your taxable income, your borrowing mix, and your strategy.
When P&I Makes Sense for Investors
IO isn’t always the answer. P&I is a better fit when:
- You’re holding long-term and don’t plan to buy again — equity building is the priority
- Your investment property is negatively geared but your tax benefit is limited — lower income, lower bracket
- IO rate premiums are significant — some lenders charge 0.10–0.30% more for IO; at higher loan sizes that adds up
- You want to demonstrate equity growth — useful if you plan to use the investment property’s equity as a deposit for future borrowing
IO Periods Don’t Last Forever
This is where investors get caught. A 5-year IO period feels like a long time when you’re signing documents. But it arrives fast. When it expires and your loan reverts to P&I, repayments jump — sometimes by $1,000+ per month on larger loans.
Successful investors don’t wait for the rollover. They review 12–18 months before expiry: refinance if better terms are available, extend IO if the lender allows, or restructure deliberately if they’re transitioning to an equity-harvesting phase.
Don’t Set and Forget
Whichever structure you choose, review it every 2–3 years. Your income changes, your tax position shifts, and lenders move rates. The loan structure that was optimal at purchase may not be optimal today.