Interest-Only Loans on Investment Property: Still Worth It in 2026, or Has the Maths Changed?

Interest-only investment loans were an almost universal recommendation a decade ago. At 3–4% interest rates, the cash flow benefit was clear: pay only interest, maximise your borrowing power, use the difference to fund the next deposit. The maths worked cleanly.

At 6–7%, the same maths produces a different answer — not always worse, but different. Whether IO still makes sense for you in 2026 depends on your specific situation: your marginal tax rate, your portfolio stage, your cash flow position, and what you plan to do with the money you're not putting toward principal.

Here's an honest breakdown of where IO loans still win, where they've lost their edge, and what to consider when your IO period expires.

An interest-only loan requires you to pay only the interest on the borrowed amount for a set period — typically 1–5 years, sometimes up to 10. At the end of the IO period, the loan reverts to principal and interest, and your repayments increase to pay down the original loan balance over the remaining term.

What IO does not do: it doesn't reduce your debt. At the end of a 5-year IO period on a $500,000 loan, you still owe $500,000. The loan isn't self-liquidating. The bet you're making is that the asset is growing faster than the principal you're not repaying — and that the cash flow benefit in the meantime was deployed productively.

This is the core issue with IO at higher rates: as rates rise, the interest cost increases, the cash flow benefit narrows, but the underlying risk — that you're not building equity through repayments — remains unchanged.

The primary case for IO on investment property is cash flow preservation. By not paying principal, your monthly outgoing is lower — and that difference can be deployed elsewhere: into an offset account on your home loan, into a deposit for the next property, or simply to maintain serviceability headroom for future borrowing.

At current rates, the cash flow difference between IO and P&I on a $600,000 investment loan over a 30-year term is approximately $1,100–$1,400 per month. That's still meaningful. At 3% rates, the difference was around $700/month — so in dollar terms, the benefit has actually increased even as the optics of IO have become less attractive.

The question is what you do with that $1,100. If it's sitting in a non-deductible home loan offset account reducing your interest on a $400,000 owner-occupied mortgage, the after-tax benefit is substantial. If it's being spent, the benefit disappears.

Interest on investment property loans is tax-deductible. This remains true whether the loan is IO or P&I — but the IO loan maximises the deductible interest relative to repayments. On an IO loan, every dollar you pay is deductible. On a P&I loan, the principal component is not.

For investors on the top marginal rate (47%), a $3,500/month IO repayment on a $600,000 loan at 7% generates approximately $1,645/month in tax offset. The after-tax cost of the loan is approximately $1,855/month. Without IO, the P&I equivalent repayment would be $4,600/month, with a smaller deductible component and a higher net cost in the early years.

The higher your marginal rate, the more valuable the deductibility argument for IO becomes. For investors in the 30–32.5% bracket, the advantage narrows considerably.

For context on how this interacts with negative gearing strategy: see what's changing for negative gearing in 2027 — the deductibility landscape is shifting and it's worth understanding before locking in a loan structure.

The biggest practical problem with IO loans in the current rate environment isn't the IO period itself — it's what happens when it ends.

When an IO loan reverts to P&I after 5 years, the remaining balance is amortised over the remaining loan term. On a 30-year loan with a 5-year IO period, the P&I repayments are calculated over 25 remaining years — not 30. On a $600,000 loan at 7%, the IO repayment is approximately $3,500/month. The P&I revert repayment is approximately $4,900/month — a 40% increase, almost immediately.

For investors who took IO loans in 2019–2021 when rates were at historic lows, this revert shock is arriving now, at rates 3–4 percentage points higher than when they signed. Many investors are facing a situation where the property's rental income no longer covers the new P&I repayment, and the cash flow shortfall has expanded significantly.

This is the risk that the IO strategy carried silently: you were not building equity through repayments, and now you're facing a much higher repayment at a much higher rate. The asset may have grown — but the loan balance hasn't shrunk.

On a $600,000 investment loan at 7.0%:

Interest-only (5-year period):
Monthly repayment: ~$3,500
Total paid over 5 years: ~$210,000
Loan balance after 5 years: $600,000 (unchanged)
Monthly repayment after revert (over 25 years): ~$4,900

Principal and interest (30 years):
Monthly repayment: ~$3,990
Total paid over 5 years: ~$239,400
Loan balance after 5 years: ~$570,000
Monthly repayment continues at: ~$3,990

The IO option saves $490/month during the IO period. Over 5 years that's $29,400 — which, deployed into a home loan offset account at 7%, saves approximately $6,000–$8,000 in non-deductible interest. Net benefit after tax: perhaps $25,000–$35,000 over the IO period, depending on your rate and tax position.

That's still a real benefit. But it comes at the cost of the revert shock and the absence of any equity build through repayments. Whether that trade-off works depends entirely on what happens to the asset's value and what you do with the freed-up cash.

IO remains the right structure in specific circumstances:

You are in active accumulation phase and have a clear next purchase. If you're planning to buy another property within 2–3 years, the IO cash flow advantage allows you to maintain borrowing capacity and save a deposit faster. The cost is deferred equity — which is acceptable if growth is doing the heavy lifting.

Your marginal tax rate is 45–47%. The deductibility benefit is maximised at top marginal rates. If you're earning above $180,000, the after-tax cost of IO interest is significantly lower than the headline rate suggests.

You have a high-balance non-deductible home loan. Every dollar of IO cash flow that offsets your owner-occupied mortgage interest generates a tax-equivalent return equal to your mortgage rate. At 6.5%, that's a guaranteed 6.5% return on the redirected cash — better than many alternatives.

Your investment property yield is strong relative to the IO rate. If you're getting 5.5% gross yield on a property and paying 6.5% IO, the gap is 1% — manageable. If yield is 3.5%, the shortfall is 3% — and IO isn't fixing that, it's masking it.

P&I is often the better structure when:

You're within 10 years of retirement. In this phase, reducing debt is more important than preserving cash flow. You want to approach retirement with as little encumbrance on the portfolio as possible. IO delays that process.

You don't have productive use for the IO cash flow saving. If the extra $1,100/month is simply going to living expenses rather than offsetting a non-deductible loan or funding a next purchase, you're not realising the IO benefit — you're just delaying debt reduction.

You're approaching an IO revert and rates are still high. If your IO period is expiring and the revert payment is materially higher than current cash flow allows, consider refinancing to P&I now and managing the transition — rather than facing the full revert shock at an inconvenient time.

Your portfolio strategy focuses on consolidation, not accumulation. See: how the three phases of property strategy — accumulation, consolidation, and income — change the optimal loan structure at each stage.

One approach that many investors overlook: P&I with a 100% offset account attached to the investment loan. This structure pays down principal — which matters for long-term debt reduction — but allows you to park cash in the offset account to reduce the effective interest without actually paying it down permanently.

If you later need the cash (for a deposit, for renovation, for an emergency), you draw from the offset rather than redrawing from the loan — which has tax implications. The flexibility is preserved, and you're building equity through the P&I repayments while managing cash flow through the offset.

This is often a better structure than IO for investors who want the flexibility of IO but also want to build equity. The downside is that offset accounts require discipline — if the money in the offset gets spent, the interest-saving benefit evaporates.

For more on how loan structure interacts with portfolio sequencing: the sequencing framework for building a property portfolio in Australia.

Interest-only investment loans still make sense for high-income investors in active accumulation who have productive use for the freed-up cash flow. The maths still works — it's just less forgiving than it was at 3% rates, and the revert risk at IO expiry is more severe in the current environment.

For investors approaching retirement, consolidating their portfolio, or without a clear deployment plan for the IO cash flow benefit, P&I — or P&I with a well-managed offset — is typically the better structural choice.

The loan structure decision should be made in the context of your whole portfolio strategy, not property by property. If you want to see how one investor structured their loans as part of a strategy that grew $200,000 in 18 months, the case study is free: ausretirementoffice.com.au.

Book a Strategy Call

If you want to pressure-test your loan structure — IO vs P&I, offset strategy, cross-collateralisation — a 20-minute call can map out the optimal setup for your situation.

Book a free 20-minute strategy call → https://www.ausretirementoffice.com.au/book

Or Download the 200K Property Case Study Here

Disclaimer: The information provided by Australian Retirement Office is general in nature and educational only. It does not constitute financial product advice, legal advice, or taxation advice, and does not take into account your objectives, financial situation, or needs. Australian Retirement Office does not hold an Australian Financial Services Licence (AFSL). Where appropriate, we may refer you to licensed professionals within our partner network. We may receive referral fees for these introductions. All investments carry risk, including potential loss of capital. Past performance is not a reliable indicator of future returns. You should obtain professional advice and review all relevant Product Disclosure Statements (PDS) before making any financial decisions.

Related reading: Negative Gearing: What's Changing in 2027 | How to Avoid CGT on Investment Property | Property Investment Strategy: What the Numbers Actually Say | How to Build a Property Portfolio: Sequence and Timing | How Many Properties to Retire