Many property investors choose interest-only loans for the cash flow advantage without fully understanding what happens to the loan balance over time. The monthly repayment is lower, which is accurate. What the repayment schedule doesn’t make obvious is that the loan balance stays exactly where it started until the interest-only period ends, at which point repayments recalculate over a shorter remaining term, often increasing sharply. Understanding both structures helps investors choose one that fits their strategy rather than just their monthly budget.
How principal and interest repayments work
On a principal and interest (P&I) loan, every repayment covers two components: the interest charged on the outstanding balance for that month, and a portion of the loan principal itself. In the early years, the interest component dominates. On a $600,000 loan at 6.3%, roughly $560 of the first monthly repayment of around $3,730 goes toward reducing the principal. That proportion gradually shifts, with more of each payment going to principal as the balance reduces.
Over a 30-year P&I loan at 6.3%, a borrower with a $600,000 starting balance would owe approximately $530,000 after 5 years and around $440,000 after 10 years, assuming rates hold roughly steady. Equity builds consistently, which increases the investor’s ability to access funds against the property for future purchases. That growing equity position is a core part of how many investors fund their second or third property acquisition.
What interest-only means for your loan balance
On an interest-only loan, repayments cover only the interest charge each month. The loan balance doesn’t reduce during the interest-only period. On the same $600,000 loan at 6.3%, the monthly interest-only repayment is approximately $3,150, compared to $3,730 on a P&I structure. The saving is roughly $580 per month, or around $6,960 per year.
At the end of a 5-year interest-only term, the balance remains at $600,000. The loan then converts to P&I repayments calculated over the remaining 25 years. At 6.3%, the new repayment would be approximately $3,940 per month, which is higher than the original P&I repayment would have been on the full 30-year term. The shorter remaining term means more principal must be repaid in each subsequent payment.
Does this mean interest-only is always more expensive over the life of the loan? Over a long hold period, yes. An investor who holds the property for 20 years and uses a 5-year interest-only period will pay more total interest than one who chose P&I from day one, because the balance stays higher for longer. The scale of that difference depends on the loan size, the rate, and what happens to property values during that time.
The cash flow difference and what it means in practice
For investors managing multiple properties, the cash flow benefit of interest-only is real. On a $600,000 investment loan, keeping an extra $580 per month in hand provides more flexibility to cover vacancies, maintenance, or body corporate levies. Across 3 properties, that margin multiplies to over $1,700 per month in additional liquidity compared to P&I on all three.
The trade-off is that the property must increase in value or the investor must build equity through other means for the overall wealth position to improve during the interest-only period. On a property that barely moves in a flat market over 5 years, an investor choosing interest-only has the same loan balance at the end of year 5 as they did at settlement. If they had chosen P&I, they would have reduced that balance by approximately $70,000 over the same period.
How lenders assess interest-only applications for investors
APRA’s lending guidelines place specific restrictions on interest-only lending. Lenders are required to assess an investor’s ability to service the loan at P&I repayments, even during the interest-only period. The serviceability calculation uses a higher notional repayment than what the borrower actually pays, which reduces assessed borrowing capacity relative to what it would be if assessed on the interest-only repayment alone.
Interest-only terms for investors are typically capped at 5 years, with some non-bank lenders offering up to 10 years in certain circumstances. After the interest-only period, the loan converts to P&I or the borrower must negotiate a new interest-only term, which involves a fresh assessment at current rates and credit criteria. A borrower who qualified comfortably in 2021 may face a different outcome at reassessment in 2026 if income has changed, debts have increased, or the lender’s policy has tightened.
Tax considerations and what to discuss with your accountant
Interest-only loans can offer a larger tax deduction for investors who negatively gear property. Because the interest component of repayments is higher relative to principal, the deductible interest expense is greater under an interest-only structure compared to P&I. For investors in higher marginal tax brackets, this can improve the after-tax cash flow position of the property meaningfully.
The interaction between loan structure, deductible interest, depreciation schedules, capital gains, and individual income varies significantly by investor. An investor holding multiple properties, using a trust or company structure, or deriving income from multiple sources faces additional complexity. A qualified accountant should model the actual after-tax position before an investor commits to either structure solely on tax grounds. The ATO’s rules on investment property deductibility can also change, as the 2018 removal of travel expense deductions for residential property investors demonstrated.
Neither structure is inherently better for every investor. The right choice depends on the investor’s cash flow needs, equity strategy, holding period, tax position, and plans for future acquisitions. These factors are worth working through carefully with both a mortgage broker and an accountant before settling on a loan structure.
Key Takeaways
- Principal and interest repayments reduce the loan balance from day one; interest-only repayments leave the balance unchanged until the interest-only period ends.
- On a $600,000 loan at 6.3%, the monthly saving from choosing interest-only over P&I is approximately $580, or around $6,960 per year.
- At the end of a 5-year interest-only term, the loan converts to P&I over the remaining 25 years, which typically produces a higher repayment than the original 30-year P&I amount would have been.
- APRA guidelines require lenders to assess investor serviceability at P&I repayment levels even during the interest-only period, which reduces assessed borrowing capacity.
- Interest-only loans can increase the deductible interest expense for negatively geared investors, but the tax impact varies significantly by individual circumstances and should be modelled with a qualified accountant.
- Interest-only terms are typically capped at 5 years and require a fresh assessment at current rates and lending criteria to extend, which may produce a different outcome than the original application.