Lower repayments now, but a higher total cost and a reversion shock later. Here is the complete picture.
The appeal of an interest-only loan is straightforward: lower monthly repayments. On a $700,000 loan, the difference between IO and P&I repayments can be $800 to $1,100 per month. For an investor managing multiple properties, that cash flow difference has real strategic value. For an owner-occupier stretched by cost-of-living pressures, it looks attractive for the same reason. But the mechanics of what you are actually deferring - and what the reversion looks like - change the calculation materially.
During the interest-only period, you pay only the interest component of your monthly repayment. The principal balance does not reduce. At the end of the IO term - typically 1 to 5 years for owner-occupiers and up to 10 years for investment loans - the loan automatically reverts to principal and interest. At that point, the lender recalculates your repayments to pay off the full original principal over the remaining loan term.
That reversion is where many borrowers are caught out. The loan term does not reset. If you took out a 30-year loan and had a 5-year IO period, your P&I repayments when you revert cover the full principal over 25 years - a shorter amortisation period than if you had been on P&I from day one, producing higher monthly repayments.
The repayment shock in numbers: A $700,000 loan at 5.7% over 30 years. IO repayments: $3,325 per month. After a 5-year IO period, P&I repayments for the remaining 25 years: $4,432 per month - a 33% increase. The principal balance is still $700,000 on the day of reversion.
The case for IO on investment loans is built on three pillars, all of which are connected to tax and cash flow strategy rather than a desire to avoid repaying debt:
The validity of each argument depends on the investor's actual tax position, the interest rate differential between their IO investment loan and their P&I owner-occupied loan, and whether they actually direct the freed cash flow to debt reduction rather than consumption.
Most owner-occupiers who use IO do so for short-term cash flow relief. The logic is understandable: if repayments are tight, paying less each month provides breathing room. But the mechanics work against the borrower in three compounding ways:
The owner-occupier scenarios where IO is genuinely justified are narrow: a documented short-term capital constraint (parental leave, a business investment phase, a property that will be sold within 3 years) where the intent and capacity to revert to P&I on a specific timeline is concrete. In practice, "short-term" IO periods have a tendency to become permanent through serial extensions, which is the worst outcome.
Since 2017, APRA has required authorised deposit-taking institutions to limit interest-only lending to 30% of new residential mortgage flows. The limit was introduced in response to the rapid growth in investor IO lending during the 2014–2017 cycle and has remained in place.
The practical consequence is that IO products carry a rate premium over equivalent P&I products - typically 0.1% to 0.4% per annum depending on the lender and whether the property is owner-occupied or investment. On a $700,000 loan, 0.3% is $2,100 per year in additional interest. That cost is in addition to the absence of principal reduction.
This is an area where lender policy variation is significant and where broker knowledge of the panel adds direct value. Some lenders assess IO loan applications at the P&I repayment rate calculated over the remaining loan term after the IO period ends. A 30-year loan with a 5-year IO period would be assessed at P&I repayments over 25 years at the assessment rate - which produces a higher monthly figure than P&I over 30 years at the same rate. That assessment approach can materially reduce borrowing power compared to a standard P&I application. Other lenders assess IO applications at the IO repayment only. The difference can be $50,000 to $100,000 in borrowing power on a single application.
Self-managed superannuation fund (SMSF) limited recourse borrowing arrangements (LRBAs) are the one context where IO is structurally required rather than a choice. Under the ATO's interpretation of non-recourse lending arrangements, the SMSF cannot make principal repayments in a way that reduces the lender's security without triggering a recourse concern. Many SMSF lenders require IO during the accumulation phase for this reason. The strategic and tax implications of SMSF property lending are distinct from standard investment lending and warrant separate advice from both a financial planner and a tax agent.
Investors who purchased in Leppington, Edmondson Park, or Oran Park during the 2022–2025 cycle - a period when IO terms were commonly written for new investment purchases - may be approaching the end of their IO period in 2026 or 2027. The reversion from IO to P&I on a $750,000 investment loan at current rates will add approximately $900 to $1,100 to monthly repayments. Reviewing the loan structure before the reversion date - rather than responding to it after the fact - is straightforwardly better.
Options at reversion include extending the IO period with the current lender (subject to a fresh serviceability assessment), refinancing to a new lender who will write a new IO term, or converting to P&I and planning for the higher repayment. Each path has different costs and tax implications.
Possibly, but not automatically. When an IO period ends, you can apply to the lender to extend it - subject to a fresh serviceability assessment at the assessment rate, your current financial position, and the lender's current credit policy. Approval is not guaranteed. Some lenders will not extend IO for owner-occupiers at all. If your financial position has changed materially since the original loan was written, the extension may be declined.
If you intend to sell within a defined short period and the IO rate differential is modest, the cash flow benefit during that period may outweigh the absence of principal reduction - particularly if the property is appreciating. However, the IO rate is typically 0.1% to 0.4% higher than the equivalent P&I rate. Over 3 years, that additional interest cost should be weighed against the monthly cash flow saving. The decision is property and rate specific, not a general rule.
You have several options, none of them guaranteed. First, approach your current lender to negotiate an IO extension - they may agree if the loan is in good standing and you can demonstrate serviceability. Second, refinance to a new lender who will write the loan on IO terms from the start of a new IO period. Third, assess whether the property should be sold if holding it is not financially sustainable. A broker can run the numbers on all three paths and identify which lenders are currently accepting IO refinance applications with your LVR and income profile.
Whether you are approaching an IO reversion, considering IO for a new investment purchase, or wanting to understand whether your current loan structure is still the right one - we can run the comparison across our full lender panel. Our Oran Park team works with investors across the Macarthur corridor.
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