Every home loan comes down to the same choice: pay interest only for a while, or start chipping away at the principal from day one. Most first-time buyers assume principal and interest is the “normal” option and interest-only is just for investors – and most of the time that’s true. But not always, and getting it wrong costs real money.
Short answer: principal and interest suits most owner-occupiers because it builds equity and costs less over the life of the loan. Interest-only suits investors and borrowers managing short-term cash flow, because it frees up money now in exchange for a bigger repayment jump later. The right call depends on what you’re borrowing for, how long you plan to hold the property, and whether you can handle repayments rising once the interest-only period ends.
This guide breaks down how each repayment type actually works, what they cost, and which one fits different situations – based on what we see day to day arranging home loans for clients across Melbourne.
What Is a Principal and Interest Loan?
With a principal and interest (P&I) loan, every repayment covers two things: a slice of the amount you borrowed (the principal) and the interest charged on the outstanding balance. Early in the loan, most of each repayment goes toward interest. As the balance shrinks, more of each repayment starts paying down principal instead.
By the end of a standard 25 or 30-year term, the loan is fully repaid. This is the default structure most Australian lenders set up unless a borrower specifically requests interest-only, and it’s what roughly 90% of new residential loans are written as, according to APRA’s quarterly lending data.
What Is an Interest-Only Loan?
An interest-only (IO) loan means your repayments cover just the interest charged for a set period – typically one to five years for owner-occupiers, and sometimes up to ten years for investors, depending on the lender. During that period, the loan balance doesn’t move. You’re not building equity through repayments; any equity gain comes purely from the property’s value rising.
Once the interest-only period ends, the loan automatically switches to principal and interest. Because the full remaining balance now has to be repaid over a shorter timeframe, repayments jump – often by 25-35%. Lenders are required to reassess your ability to service that higher repayment before approving an interest-only term, and most banks maintain their own internal risk limits on interest-only lending in line with APRA’s prudential guidance, so it’s not something every applicant will be approved for automatically.
Interest-Only vs Principal and Interest: Key Differences
| Principal & Interest | Interest-Only | |
| Monthly repayment | Higher | Lower during IO period |
| Loan balance | Reduces over time | Stays the same during IO period |
| Total interest paid | Lower | Higher |
| Typical interest rate | Slightly lower | Often 0.3-0.5% higher |
| Equity built through repayments | Yes | No, until P&I resumes |
| Best suited to | Owner-occupiers | Investors, short-term cash flow needs |
| Repayment shock risk | None | Yes, when IO period ends |
The rate gap matters more than people expect. Lenders generally price interest-only loans higher because they carry more risk – the bank isn’t recovering any principal during that period. Over a full loan term, that difference compounds.
The Real Cost Difference: A Working Example
Take a $600,000 loan over 25 years. On principal and interest from day one, you’re steadily reducing the balance and paying interest on a shrinking amount. Take the same loan with five years interest-only first, and two things happen: you pay interest on the full $600,000 for those five years instead of a reducing balance, and you only have 20 years left to repay the principal once P&I kicks in – not 25.
The result is a noticeably higher monthly repayment for the remaining term, and tens of thousands more paid in interest over the life of the loan compared to starting P&I straight away. It’s not a small gap. This is why interest-only rarely makes sense as a “cheaper” option long-term – it’s a cash-flow tool for a specific window, not a way to save money overall.
Who Should Consider Interest-Only?
Interest-only tends to suit a narrower group of borrowers than people assume:
- Property investors who want to maximise cash flow during the loan term and use the interest as a tax deduction, particularly while a property is negatively geared
- Investors planning to sell within a few years rather than hold long-term, where paying down principal offers little benefit before the sale
- Borrowers with irregular or seasonal income – self-employed clients or those on commission, who need lower fixed repayments during leaner months
- Anyone temporarily reducing repayments during a life event, such as parental leave, provided the lender approves it and there’s a clear plan for when the IO period ends
What interest-only is not suited to is a first home buyer trying to “afford” a property they otherwise couldn’t. If the only way you qualify for a loan is by starting interest-only, that’s usually a sign the loan amount or the property needs rethinking, not the repayment structure.
Who Should Consider Principal and Interest?
For most owner-occupiers, P&I is the more sensible default, and it’s what we recommend to the large majority of clients buying a home to live in. Reasons it tends to win out:
- You start building real equity from the first repayment, not years later
- Lenders generally price it lower, so more of your repayment works for you
- There’s no repayment shock waiting at the end of a fixed period
- It forces disciplined debt reduction, which suits most household budgets better than an interest-only gap that gets filled with other spending
The trade-off is a higher repayment from day one. For some buyers stretching to get into the market, that’s a genuine constraint – which is exactly the kind of scenario worth working through with a broker before locking in a structure.
What Happens When the Interest-Only Period Ends
This is the part that catches people out. When an IO term expires, the loan reverts to principal and interest automatically, calculated over whatever term is left. If you took a 30-year loan with five years interest-only, you now have 25 years to repay the full balance – and repayments rise to reflect that.
Borrowers who haven’t planned for it can face real financial pressure at this point, especially if interest rates have also moved during the IO period. Before an interest-only term starts, it’s worth mapping out three things: what the repayment will look like once it converts, whether your income will support that increase, and whether refinancing, extending the IO period, or switching lenders might be an option closer to the deadline. None of those decisions should be made in the final few weeks – they need a plan well in advance.
How a Mortgage Broker Helps You Decide
This isn’t a decision with one right answer – it depends on your income pattern, whether the property is for living in or investing, how long you plan to hold it, and how much repayment flexibility you actually need versus think you need.
We walk clients through the numbers on both structures side by side, using their real income, existing debts and goals, rather than a generic rule of thumb. For investors, we also look at how the repayment structure interacts with negative gearing and portfolio growth plans; for owner-occupiers, the focus is usually on serviceability and getting into P&I as early as realistically possible.
If you’re weighing this up for an investment property specifically, our investment loans guide covers how lenders assess IO applications for investors in more detail, and our recent piece on interest-only home loans in Melbourne looks at whether the strategy still stacks up in the current rate environment.
Frequently Asked Questions
Is interest-only more expensive than principal and interest?
Over the life of the loan, yes. You pay interest on a higher balance for longer and typically face a slightly higher interest rate, so total interest paid ends up higher than starting P&I from day one.
Can I switch from interest-only to principal and interest early?
Usually yes. Most lenders allow you to move to P&I before the interest-only period ends, and doing so sooner reduces the total interest you’ll pay.
Do first home buyers ever get approved for interest-only loans?
It’s uncommon and generally not recommended. Most lenders and brokers steer first home buyers toward principal and interest, since building equity from the start better supports long-term serviceability.
How much do repayments increase when interest-only ends?
It varies by loan size, rate and remaining term, but a jump of 25-35% is typical, since the full balance now needs to be repaid over a shorter period.
Does interest-only affect how much I can borrow?
It can. Because lenders must assess your ability to service the higher post-IO repayment, some borrowers find their maximum loan amount is actually lower under an interest-only structure than under standard P&I.
Talk Through Your Options With Ace Finance Solutions
Choosing between interest-only and principal and interest isn’t something to decide from a blog post alone – it needs to be run against your actual income, goals and timeline. If you’d like that worked through properly, get in touch for a free consultation and we’ll map out what each option would realistically look like for you.
