Interest-Only vs Principal and Interest Home Loans 2026: Which Is Better

The choice between an interest-only (IO) and a principal-and-interest (P&I) home loan affects your monthly cash flow, the total interest you pay over the life of the loan, your tax position if the property is an investment, and even how much you can borrow. An IO loan slashes your monthly repayments by roughly 15%–20% but costs you significantly more in total interest if held to term.

If you are comparing “interest-only vs principal and interest home loan” options in Australia in 2026, this guide uses real numbers to show the repayment difference, total interest impact, tax treatment for investors, APRA’s current stance on IO lending, and the scenarios where each loan type makes sense.

The Repayment Difference: A Real Numbers Example

Let’s start with the core comparison. We take a $500,000 loan at 6.00% over a 30-year term:

Interest-only repayments: With an IO loan, you pay only the interest each month and the principal remains unchanged. The monthly payment is simply the principal multiplied by the monthly interest rate: $500,000 × (6.00% ÷ 12) = $2,500 per month. Every dollar of that $2,500 goes to interest. After 5 years of IO repayments totalling $150,000, your loan balance is still $500,000 — you have paid $150,000 in interest and not a cent of principal.

Principal-and-interest repayments: With a P&I loan, each repayment covers both the interest and a portion of the principal. Using the amortisation formula, the fixed monthly repayment on a $500,000 loan at 6.00% over 30 years is approximately $2,998 per month. After 5 years, your loan balance has reduced to approximately $465,000 — you have paid approximately $147,000 in interest and reduced the principal by roughly $35,000.

The monthly difference: $2,998 P&I minus $2,500 IO equals $498 per month — a 17% reduction in monthly repayment by choosing IO.

Over the 5-year IO period: IO costs $150,000 in interest-only payments with no principal reduction. P&I costs approximately $180,000 in total repayments ($147,000 interest plus $33,000 principal) and you own $35,000 more of your home.

Total Interest Over the Full Loan Life

If a borrower pays IO for 5 years and then P&I for the remaining 25 years, the total interest paid is substantially higher than if they had paid P&I from day one. Here is the comparison for a $500,000 loan at 6.00%:

Full P&I for 30 years: Total interest paid is approximately $579,000. Total repayments are approximately $1,079,000. The loan is fully repaid at the end of year 30.

IO for 5 years, then P&I for 25 years: First 5 years: $150,000 in interest-only payments, loan balance still $500,000. Next 25 years: P&I repayments on $500,000 over a shortened remaining term of 25 years — monthly repayment of approximately $3,221, with total interest over the 25-year P&I period of approximately $466,000. Total interest over the full 30 years: $150,000 + $466,000 = $616,000. That is approximately $37,000 more than the all-P&I path.

The longer the IO period and the larger the loan, the bigger the interest penalty. On an $800,000 investment property loan with a 10-year IO period, the total interest premium compared to all-P&I can exceed $100,000.

Tax Deductibility: The Investor’s Lens

For investment properties, the analysis changes because interest is tax-deductible. The key insight for investors is:

Interest is deductible. Principal is not. Every dollar of interest you pay on an investment property loan reduces your taxable income (at your marginal tax rate). Every dollar of principal you repay on the same loan is a non-deductible use of your cash.

This creates a powerful incentive for investors to use IO loans. By keeping repayments to interest-only, the investor maximises the deductible interest expense and frees up cash that would have gone to principal. That freed-up cash can be directed to:

• Paying down the non-deductible PPOR loan faster (the most tax-efficient use)
• Investing in other income-producing assets
• Funding renovations that increase the property’s value and rental yield

Consider an investor in the 37% marginal tax bracket (taxable income $135,000–$190,000 in 2026–27) with a $600,000 investment property loan at 6.00%:

• IO at $3,000/month: All $36,000 per year in interest is deductible. At 37%, the tax saving is approximately $13,320, making the after-tax cost of the loan approximately $22,680 per year.
• P&I at $3,597/month: In the first year, approximately $35,800 is interest (deductible, saving approximately $13,246 in tax) and approximately $7,400 is principal (not deductible). After tax, the cost is approximately $29,918 — roughly $7,200 more after-tax cash outlay than the IO option.

The investor preserves approximately $7,200 in annual cash flow by choosing IO, which can be directed to their PPOR loan, where every dollar of principal repayment saves non-deductible interest at 6.00% — a guaranteed 6.00% after-tax return.

This is the logic behind the standard advice: minimise investment loan debt (deductible) and maximise PPOR loan repayments (non-deductible). IO on the investment loan is the tool that enables this strategy.

APRA Caps and the Current IO Lending Environment

In March 2017, APRA imposed a benchmark limiting IO lending to 30% of new residential lending, in response to concerns about speculative investor lending and housing market risks. The cap was lifted in January 2019 after APRA judged that lending standards had improved sufficiently.

In 2026, IO lending has normalised at approximately 15%–20% of new lending, down from nearly 40% at the 2015 peak. Individual lenders maintain their own internal limits and continue to price IO loans with a premium:

• IO rate premium (owner-occupier): Typically 0.20%–0.50% above the equivalent P&I rate.
• IO rate premium (investor): Typically 0.10%–0.30% above the equivalent P&I investor rate.

IO loans also face stricter serviceability assessment. Lenders typically assess an IO loan application by assuming the loan will revert to P&I over the remaining term and checking that you can afford the higher P&I repayments — with the 3% serviceability buffer on top. This means an IO applicant must qualify at the higher P&I repayment level, even though they will initially pay the lower IO amount. This limits the extent to which IO can increase your borrowing power.

When an Interest-Only Loan Makes Sense

IO loans are not inherently good or bad — they are a tool that fits specific circumstances. Here is when they make sense:

Investment property (the classic use case). The tax efficiency of IO for investors is well established. If you own both a PPOR and an investment property, using IO on the investment loan and directing all surplus cash to your non-deductible PPOR loan is the optimal tax strategy for most investors. The cash flow benefit also makes IO attractive for negatively geared properties where rental income does not cover P&I repayments.

Short-term cash flow management (PPOR). If you are experiencing a temporary reduction in household income — a parent on parental leave, a career change, or a period of study — switching to IO for 1–3 years can cut your mortgage repayments by 15%–20% without needing to refinance or sell. The key is having a credible plan to return to P&I once income recovers.

Bridging finance. When you are buying a new home before selling your existing one, a bridging loan is typically structured as IO during the bridging period (usually 6–12 months). This minimises your repayments while you carry two properties.

Converting PPOR to investment property. If you plan to move out of your current home and rent it out, switching to IO before the conversion preserves the higher loan balance (maximising future deductible interest) and improves the property’s cash flow as a rental. This strategy works hand-in-hand with using an offset account rather than a redraw facility to preserve the loan’s deductibility — our offset vs redraw guide explains this in detail.

When Principal and Interest Makes More Sense

Owner-occupied home, long-term hold. If you plan to live in your home for the long term and it will never become an investment property, P&I is the straightforward choice. You build equity with every repayment, the interest rate is lower, and you avoid the repayment shock when the IO period ends.

You are aiming to be mortgage-free. Paying P&I forces you to build equity and reduces the loan balance every month. An IO loan keeps you in debt at the original amount indefinitely (during the IO period), which is psychologically and financially at odds with the goal of debt freedom.

You need a lower interest rate. P&I rates are consistently lower than IO rates by 0.10%–0.50%, compounding to a meaningful difference over time.

You want maximum borrowing power. While IO reduces your monthly payments, lenders assess you at the higher P&I repayments anyway, so IO does not directly increase your maximum loan amount under APRA’s serviceability rules. In fact, the rate premium on IO loans slightly reduces your assessed surplus and therefore your borrowing power. For a detailed breakdown of 2026 borrowing limits, see our borrowing power guide.

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Use the Mortgage Repayment calculator to compare interest-only vs principal-and-interest repayments on your loan amount and see the exact monthly and lifetime cost difference. Visit /calculators/mortgage-repayment/ to model your scenario.

Disclaimer

Disclaimer: This article provides general estimates only and does not constitute financial, tax, or legal advice. Rates, thresholds, and rules change. Always refer to the ATO, your state revenue office, or a licensed professional for your specific circumstances. Last updated: July 2026.