One of the most important decisions when structuring a home loan is whether to choose interest-only (IO) or principal and interest (P&I) repayments. The choice affects your monthly cash flow, total interest paid, how quickly you build equity, and your tax position if the property is an investment. At Mortgage & Finance Advisory, we help property buyers and investors across Geelong, the Surf Coast, Melbourne, and regional Victoria choose the repayment structure that best matches their financial strategy and goals.
This guide compares IO and P&I loans in detail: how each works, the real cost difference over time, when IO makes financial sense, and the risks to be aware of.
With a P&I loan, each monthly repayment covers two components: the interest charged on the outstanding balance, and a portion of the principal (the amount you originally borrowed). In the early years, most of your repayment goes toward interest, with a small amount reducing the principal. As the loan progresses and the balance decreases, the proportion shifts: more goes to principal and less to interest.
On a $600,000 loan at 6.19% over 30 years, your monthly P&I repayment would be approximately $3,670. In the first month, roughly $3,095 covers interest and only $575 reduces your principal. By year 15, approximately $1,900 goes to interest and $1,770 to principal. By year 25, the split reverses with most of the payment reducing your balance. Over the full 30 years, you’d pay approximately $721,000 in total interest.
With an IO loan, your monthly repayments cover only the interest, none of the principal. Your loan balance stays the same throughout the IO period. Using the same $600,000 loan at 6.49% (higher rate for IO), your monthly payment during the IO period would be approximately $3,245, about $425 less than the P&I option each month.
However, when the IO period ends (typically after 1-5 years), the loan reverts to P&I repayments. But now you’re repaying the full $600,000 over the remaining term (say 25 years instead of 30). This means your repayments jump to approximately $4,070 per month, a $825 increase from the IO period. Many borrowers are caught off guard by this payment shock when their IO period expires.
| Feature | P&I (6.19%, 30 years) | IO 5 years then P&I (6.49%/6.19%, 30 years) |
|---|---|---|
| Loan amount | $600,000 | $600,000 |
| Monthly payment (years 1-5) | $3,670 | $3,245 |
| Monthly payment (years 6-30) | $3,670 | $4,070 |
| Total interest paid | ~$721,000 | ~$815,000 |
| Balance after 5 years | ~$554,000 | $600,000 (unchanged) |
| Extra interest cost | N/A | ~$94,000 more |
The IO option saves approximately $425 per month during the first 5 years ($25,500 total), but costs approximately $94,000 more in total interest over the life of the loan. For owner-occupiers, this is rarely a good trade-off. For investors, the calculation changes when you factor in tax deductions and what you do with the cash flow savings.
This is the primary use case for IO loans. Interest on investment property loans is tax deductible, while principal repayments are not. By choosing IO, the entire repayment is deductible, maximising your tax benefit. The monthly cash flow savings can be redirected to paying down your non-deductible owner-occupied home loan faster, invested in offset accounts, or used to build deposits for additional investment properties.
If you’re expecting a temporary income reduction (maternity leave, career transition, starting a business), an IO period can reduce your committed monthly outgoings during that period. Once your income recovers, you switch back to P&I. This should be a planned strategy rather than a reaction to financial stress.
During a renovation period when the property isn’t generating rental income, IO keeps your carrying costs lower. Once the renovation is complete and the property is tenanted (or sold), you either switch to P&I or dispose of the property.
An investor in Geelong had both an owner-occupied home ($450,000 loan at P&I) and an investment property ($380,000 loan also at P&I). By switching the investment loan to IO and directing the $520 per month cash flow saving into their owner-occupied offset account, they reduced the non-deductible interest on their home loan while maintaining the full tax deduction on the investment loan. Over 5 years, this strategy saved them approximately $18,000 in after-tax interest costs, despite the IO rate being slightly higher.
For owner-occupied homes: Unless you have a specific strategic reason (like an investment debt recycling strategy), IO on your home means you’re not building any equity through repayments. Your only equity growth comes from property value appreciation, which isn’t guaranteed. You’re essentially renting money from the bank without making any progress on owning your home.
When you can’t handle the payment jump: If your budget is already tight at IO repayment levels, the 20-30% increase when it converts to P&I could cause real financial stress. Lenders assess your serviceability at the P&I rate, but life circumstances can change.
In a flat or declining market: If property values aren’t growing, IO means you’re not reducing your debt while also not gaining equity through capital growth. This can lead to negative equity situations where you owe more than the property is worth.
Since APRA tightened lending standards, obtaining IO loans has become more difficult. Lenders now assess your ability to repay at the P&I rate over the remaining term (not the full original term), which reduces your borrowing capacity compared to a straight P&I application. Most lenders limit IO periods to a maximum of 5 years for investment loans and 1-2 years for owner-occupied loans. The maximum LVR for IO loans is typically 80% (compared to 95% for P&I), and interest rates carry a premium of 0.25-0.50% above the equivalent P&I rate.
Choosing between interest only and principal and interest repayments isn’t the same decision for everyone. Here’s a practical framework to help you determine which option best suits your situation right now.
You’re purchasing an investment property and want to maximise tax-deductible interest while building equity in your owner-occupied home first. You have a clear strategy for using the freed-up cash flow productively, whether that’s paying down non-deductible debt faster, investing in assets that generate returns exceeding your mortgage rate, or building a deposit for your next property purchase. You’re in a temporary cash flow squeeze (such as starting a business, parental leave, or a career transition) and need breathing room for a defined period. You understand and accept that your loan balance won’t decrease during the interest only period.
You want the security of knowing your loan balance is decreasing with every payment. You’re living in the property as your home and the interest isn’t tax-deductible. You prefer lower total interest costs over the life of the loan. You want access to the lowest available interest rates, as many lenders offer better rates on P&I loans. You don’t have a specific investment strategy that requires the additional cash flow from lower IO payments.
Interest only loans are most commonly used as part of a broader property investment strategy. Here’s how experienced investors typically structure their finance to maximise both cash flow and tax efficiency.
The debt recycling approach. This involves keeping investment property loans on interest only (maximising the tax-deductible debt) while directing all extra cash flow toward paying down your non-deductible home loan faster. Once the home loan is paid off, you can then convert investment loans to P&I or use the freed-up home equity for further investments. The mathematical advantage can be substantial: every dollar of non-deductible interest you eliminate saves you more than a dollar of deductible interest, because the deductible interest provides a tax offset.
Managing multiple properties. Investors with multiple properties often use a combination of interest only and P&I across their portfolio. Properties with higher growth potential might be kept on interest only to maximise leverage, while properties approaching the end of their growth cycle might switch to P&I to build equity ahead of a potential sale or refinance. The key is having a deliberate strategy rather than defaulting to the same structure across all properties.
The cash buffer strategy. Some investors keep their loans on interest only and park the difference (what they would have paid in P&I) in an offset account linked to their home loan. This achieves the same interest saving as making P&I payments on the home loan, but with the added flexibility of being able to access those funds if needed. It gives you tax-efficient structuring with accessible reserves.
This is one of the most important considerations that many borrowers overlook. When your interest only period expires (typically after 1-5 years), you have three options.
Option 1: Switch to P&I on the remaining term. This is the default if you take no action. Your repayments will increase because you’re now paying both principal and interest, compressed into the remaining loan term. If you had a 30-year loan with a 5-year IO period, you’ll repay the principal over 25 years instead of 30, making the P&I payments higher than if you’d been on P&I from the start.
Option 2: Extend the interest only period. If your lender approves, you can extend for another IO term. However, lenders have tightened their criteria for IO extensions, and you may need to demonstrate that you still have a valid reason for IO repayments and that you can comfortably afford the eventual P&I payments.
Option 3: Refinance. Moving to a new lender with a fresh IO period resets the clock. This is common among investors but comes with refinancing costs (typically $500-$2,000 in discharge and application fees) and requires a fresh assessment of your borrowing capacity under current lending criteria.
Using IO without a plan. Interest only should be a deliberate strategic choice, not a way to afford a property you can’t really afford on P&I terms. Always ensure you can comfortably afford the P&I repayments before committing to an IO loan.
Forgetting about the rate cliff. When IO converts to P&I, the payment increase can be 30-50%. Budget for this transition and start preparing well before the IO period expires.
Using IO for your home loan without offsetting. If you’re on IO for your owner-occupied home and not directing the saved cash flow into an offset account or other productive use, you’re simply paying more interest over the loan’s life with no strategic benefit.
Assuming IO will always be available. Lending regulations change, and access to IO loans has been restricted at various points. Don’t build a long-term strategy that relies on indefinite access to IO terms.
Yes, most IO loans allow you to make additional payments that reduce the principal. This gives you the flexibility of lower minimum payments while still paying down the loan when cash flow allows. However, some IO loans have redraw restrictions, so check the terms before relying on this feature.
Yes, you can typically switch to P&I at any time without penalty. This is useful if your circumstances change and you want to start building equity or if you’ve achieved your short-term cash flow objective.
This depends on your lender’s policy and your financial position at the time. Some lenders allow IO extensions, but you’ll need to reapply and meet their current lending criteria. It’s not automatic, and repeated IO extensions are increasingly scrutinised by lenders.
P&I builds equity faster because you’re reducing the principal with every payment. After 5 years on a $600,000 P&I loan, you might owe $554,000, which is $46,000 in equity from repayments alone (plus any capital growth). After 5 years on IO, you still owe the full $600,000, with equity only coming from property value increases.
You should plan for this transition well in advance. Options include refinancing to a new IO period (if you qualify), refinancing to a different lender with better P&I rates, extending the loan term to reduce P&I payments, or selling the property if it no longer fits your financial situation. Contact your broker several months before your IO period expires to explore options.
We’ll model both IO and P&I scenarios for your specific situation, showing the real cost difference and helping you choose the structure that matches your strategy.
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About the Author
Melanie McNaughton is the founder of Mortgage & Finance Advisory, helping home buyers and investors across Geelong, the Surf Coast, Melbourne, and regional Victoria structure their loans for optimal financial outcomes. Melanie’s expertise in loan structuring ensures clients choose the right repayment type for their specific goals and circumstances.
