Interest-Only vs Principal and Interest Loans for Investors

01Two Ways to Structure an Investment Loan

Most Australian investment loans can be structured as either interest-only or principal and interest, and the choice affects your monthly cash flow, how quickly you build equity through repayments, and how a lender assesses how much you can borrow.

With a principal and interest loan, each repayment covers both the interest charged for the period and a portion of the original amount borrowed, so the loan balance steadily reduces over the life of the loan. With an interest-only loan, repayments cover only the interest charged, and the loan balance stays the same throughout the interest-only period, which is typically set for a fixed number of years (often somewhere in the vicinity of one to five years, depending on the lender and loan) before reverting to principal and interest.

02Why Investors Sometimes Choose Interest-Only

The most common reason investors choose interest-only, at least for an initial period, is cash flow management. Because interest-only repayments are lower than an equivalent principal and interest repayment on the same loan amount, choosing interest-only frees up cash each month, which can matter for a few reasons:

• Managing a negatively geared property. If a property is already running at a loss before considering loan repayments, minimising the cash outflow during the years you're most reliant on future growth can make the holding period more manageable. This connects directly to the broader negative gearing strategy many investors are pursuing.
• Serviceability for further purchases. Lower repayments on an existing property can, in some cases, leave more borrowing capacity available for a subsequent purchase, though lenders often factor in the eventual step-up to principal and interest when assessing this, which limits how much this actually helps.
• Short holding period strategies. An investor planning to sell within a few years, for example as part of a renovate-and-sell approach, may see less value in paying down principal on a loan they don't intend to hold long-term.

03The Repayment Shock Risk

The most significant risk with interest-only lending is what happens when the interest-only period ends. Repayments typically step up to cover both principal and interest, calculated over the remaining loan term, which is now shorter than the original term. Because the remaining term has shrunk but the loan balance hasn't reduced (since no principal was paid down), the new repayment can be a noticeably larger jump than investors sometimes expect, commonly referred to as repayment shock.

This risk is compounded if interest rates have also risen during the interest-only period, or if the investor's financial circumstances have changed. The practical takeaway is to know your interest-only end date well in advance, and to actively plan for the transition, reviewing your budget, considering whether to extend the interest-only period (not guaranteed and generally requires a fresh application), refinance, or simply prepare for the higher repayment, rather than treating the switch as a problem for future you.

Our mortgage repayment calculator can help you model what the principal and interest repayment will look like once an interest-only period ends, so you can budget for it well ahead of time rather than being surprised.

04How Lenders Assess Serviceability Differently

Lenders generally don't assess interest-only loans based on the low interest-only repayment alone. Because the loan will eventually step up to principal and interest, most lenders calculate serviceability using the higher repayment that will apply after the interest-only period ends, and over the shorter remaining term, essentially testing whether you could handle the eventual, larger repayment, not just the current one.

This means choosing interest-only doesn't necessarily increase how much you can borrow compared to principal and interest, and in some cases it can actually reduce it, since the assessed repayment is higher, not lower, than a standard principal and interest loan calculated over the full original term. This is a common misconception worth clearing up before assuming interest-only is a straightforward way to boost borrowing capacity.

05Which Structure Fits Your Situation

Neither structure is universally better. Interest-only can suit investors focused on near-term cash flow, particularly those managing a negatively geared property as part of a longer growth thesis, while principal and interest suits investors who want to steadily build equity and reduce debt over time, and who may prefer the certainty of knowing their repayment isn't going to step up later.

This decision connects closely to your broader lending setup, including LVR and whether LMI applies, both covered in our guide to LVR and lending for investors in Australia. As with most lending decisions, the right structure depends on your specific cash flow, goals and risk tolerance, and it's worth discussing with a mortgage broker who can model both options against your actual numbers.

06Reviewing the Decision Over Time

Choosing interest-only or principal and interest at settlement isn't necessarily a permanent, set-and-forget decision. Many investors revisit the structure periodically, particularly around the time an interest-only period is due to expire, or when their income, goals or the broader portfolio has changed enough to warrant a different approach. Refinancing to extend an interest-only arrangement, switching to principal and interest earlier than required to start building equity faster, or restructuring across multiple properties as a portfolio grows are all things worth discussing periodically with a mortgage broker rather than assuming the original loan structure should simply run its course untouched.

07The Bottom Line

Interest-only loans free up cash flow in the short term but don't reduce your loan balance and typically lead to a step-up in repayments once the interest-only period ends, an increase worth planning for well ahead of time. Principal and interest loans cost more per repayment but steadily build equity from day one. This article is general education about how the two structures work, not personalised financial or lending advice.