Interest Only Loan Investment Property Australia: I It Still Worth It?

Interest-only loans have been a cornerstone of Australian property investment for decades. They preserve cash flow during the growth phase of a portfolio, allowing investors to hold more properties simultaneously and reinvest surplus income into the next acquisition.

But with interest rates elevated from their 2021 lows, some investors question whether IO loans still make sense. Here's how they work, where they fit in a property retirement strategy, and when to switch to principal and interest.

How Interest-Only Loans Work

An interest-only loan requires you to pay only the interest component each month — you make no reduction to the principal. At the end of the IO period (typically 1–5 years, up to 10 for investment properties), the loan reverts to principal and interest, and repayments increase significantly.

Example: A $600,000 loan at 6.5% interest-only costs approximately $3,250/month. The same loan on P&I over 25 years would cost approximately $4,050/month — a $800/month difference that can be used to fund another deposit, build a buffer, or offset against rental income while the property grows.

The Cash Flow Argument for IO Loans

The core case for interest-only is straightforward: during the growth phase of property investment, your goal is to hold the asset while it appreciates, not to reduce debt. Paying down principal locks up capital that could be deployed elsewhere.

For negatively geared properties, the lower IO repayment also reduces the net cash shortfall, making the holding cost more manageable. The tax deductibility of investment loan interest applies equally to IO and P&I loans — but IO loans maximise the interest deduction in any given year.

For more on how negative gearing and tax deductions work: Negative Gearing Investment Property Australia: How It Works and Who Benefits

When IO Loans Work Best

Growth phase investing. If you're in the accumulation phase — buying properties over a 10–20 year horizon with the goal of arriving at retirement with a portfolio — IO loans make the most sense. The priority is holding quality assets in growth markets, not reducing debt.

Multiple properties. IO loans allow you to hold more assets simultaneously. If P&I repayments would strain your cash flow and limit you to 2 properties, IO might let you hold 3 — each growing in value, each generating rental income.

High-income earners with strong cash flow. If your income comfortably services the IO repayments with surplus left over, IO loans are a powerful tool. The surplus can go into an offset account (reducing effective interest while remaining accessible) or fund additional deposits.

When IO Loans Become a Problem

IO loans become problematic when: you're approaching retirement without a clear debt reduction plan; you rely on IO payments to make properties barely serviceable; or you're not building any equity through principal reduction and capital growth has been modest.

The reversion risk is real. When an IO period ends and the loan reverts to P&I, repayments can jump 20–30%. If you haven't modelled this in your cash flow projections, the reversion can cause genuine financial stress.

Banks also assess new IO loans at higher stressed rates than P&I loans. Each IO extension requires lender approval, and serviceability standards have tightened significantly since 2018. Refinancing from IO to IO at a new lender may be harder than you expect.

IO Loans and the Property Retirement Strategy

The most effective use of IO loans in a retirement strategy follows a clear arc: accumulate using IO during the growth phase; in the 7–10 years before retirement, begin switching properties to P&I to systematically reduce debt; retire with unencumbered or near-unencumbered assets generating net rental income.

A common error is staying on IO too long. Investors who roll IO periods for 15+ years arrive at retirement with large loan balances, no principal reduction, and rising repayments. The IO loan served its purpose in years 1–10 but became a liability in years 11–20.

For the full retirement strategy framework: How to Retire Through Property in Australia

For how many properties you need in the portfolio: How Many Investment Properties Do You Need to Retire in Australia?

IO vs Offset: The Better Strategy

The most sophisticated approach isn't to choose between IO and P&I — it's to take an IO loan and attach a 100% offset account. Your surplus income sits in the offset, reducing the interest charged (as if you were paying down principal) while remaining liquid for your next acquisition or buffer.

This means you get the low repayment of an IO loan, the effective interest savings of a P&I loan, and the flexibility to access that accumulated offset at any time. Offset accounts are fully redrawable — they don't reduce your available equity but they reduce your interest bill daily.

What Has Changed in 2025–2026

Interest rates are materially higher than they were in 2021–2022. IO investment loan rates now typically sit between 6.5–7.5% for most borrowers, compared to 3–4% at the pandemic lows. This changes the cash flow calculation significantly.

APRA serviceability buffers remain tight. Banks assess new investment loans at a 3% buffer above the actual rate, meaning a 7% IO investment loan is stress-tested at 10%. This limits how much investors can borrow relative to their income.

Despite higher rates, IO loans remain the preferred structure for most professional property investors in the growth phase. The logic hasn't changed — what's changed is that the margin between IO benefit and holding cost is tighter, making market selection and yield quality more important than ever.

For property investment strategy in this environment: Property Investment Strategy Australia: A Step-by-Step Guide

General advice disclaimer: This article is general in nature and does not constitute financial advice. Australian Retirement Office does not hold an Australian Financial Services Licence. Please consult a licensed financial adviser and mortgage broker before making any loan or investment decision.

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Related reading: Negative Gearing Investment Property Australia | How to Retire Through Property | Property Investment Strategy | How Many Investment Properties to Retire