Principal & Interest vs Interest Only Australia 2026: Which Saves More?
Principal and interest repays both parts each month; interest-only (IO) pays only the interest, deferring principal for 1-5 years. IO gives bigger tax deductions for investors — but costs more overall. Here is when each makes sense in 2026.
| Factor | Principal & Interest | Interest Only |
|---|---|---|
| Monthly repayment structure | Interest + principal | Interest only; principal at end of IO period |
| 2026 typical rate (owner-occupier) | 5.8-6.2% | 6.1-6.7% (premium of 30-50 bps) |
| 2026 typical rate (investor) | 6.1-6.5% | 6.4-7.0% |
| Monthly repayment ($500k, 30yr) | ~$2,990 (at 6%) | ~$2,500 (at 6%) during IO period |
| Builds equity | Yes — every month | No — balance unchanged until IO ends |
| Tax deduction (investor) | Only interest portion | Full repayment is interest — larger deduction |
| Owner-occupier tax benefit | None — interest not deductible | None — interest not deductible |
| Typical IO term | N/A | 1-5 years, then reverts to P&I |
| Best for | Owner-occupiers; investors with surplus cash flow | Property investors maximising deductions and cash flow |
Our Verdict
Owner-occupiers should almost always choose principal and interest — the interest is not tax-deductible, there is no benefit to paying more in interest, and you build equity with every payment. Interest-only makes sense almost exclusively for property investors using negative gearing: the larger interest deduction reduces taxable income, and cash flow freed up can be redirected to non-deductible debt (your own home) or further property investment. Even for investors, limit IO periods to 1-2 years at most and always have a clear plan to switch back to P&I before the IO term expires — otherwise you will face a brutal payment shock.
Why this comparison matters
APRA cracked down on IO lending in 2017 and again in 2023, but IO remains a major strategic tool for Australian property investors. The wrong structure on a $800,000 investment loan can leak $20,000+ in unnecessary interest over a 30-year horizon.
Quick Verdict
Owner-occupiers: P&I always. Investors: IO for 1-2 years if you have non-deductible debt or multiple investment properties; otherwise P&I.
When Principal & Interest wins
- You live in the property (owner-occupier) — interest is not deductible, so no benefit to maximising it.
- You are an investor with a single property and no non-deductible debt (no owner-occupier mortgage).
- You want to build equity steadily and reduce total interest paid.
- You are near retirement and want the loan paid off.
When Interest Only wins
- You are an investor with multiple properties, negatively geared.
- You still have a non-deductible owner-occupier mortgage — IO on investment frees cash to pay that down first.
- You are in the construction phase of a new build (IO until completion is standard).
- You want to maximise current cash flow for redeployment (more property, shares, or offset).
The cost math
$500,000 investor loan, 30-year term. P&I at 6.2%: ~$3,060/month, $602,000 total interest. 5-year IO at 6.5% then P&I at 6.2%: $2,708/month during IO, rising to $3,250/month after, $657,000 total interest — $55,000 more. But that $55,000 may be largely offset by tax savings if you're in the 37-47% bracket. Model in the mortgage calculator.
FAQs
What happens after IO ends? The loan reverts to P&I over the remaining term — monthly payments jump 20-40%. This is called the "IO cliff" and has been a major regulator concern.
Can I extend IO? Yes, but it requires reassessment under current serviceability rules and is not guaranteed.
Why is the IO rate higher? APRA forces banks to price higher to discourage IO — a policy response to the 2017 housing risk build-up.
Is IO still allowed? Yes, but tightly regulated. Investor IO new lending is capped at under 30% of bank flow.
Model tax benefits in the negative gearing calculator.