Choosing how an investment loan is repaid is really three decisions in one: how much must leave your account each month, whether the balance shrinks while you hold the property, and how much your repayments change when a concession period runs out. The structures themselves are straightforward. The part that catches investors out is timing — especially the moment an interest-only period expires and the loan converts.
This guide compares principal and interest, interest-only and offset arrangements in property-investment terms. It draws on MoneySmart's consumer guidance on interest-only home loans, the Australian Government's money guidance website, and deliberately leaves tax out of scope. It is general information, not personalised advice.
What each structure does to the loan
Principal and interest. Each repayment covers the interest charged for the period plus a portion of the balance itself. Over time the balance falls, so a growing share of each repayment goes to principal. If every repayment is made as agreed, the loan is cleared by the end of the term. In one MoneySmart worked example, a borrower weighing an interest-only period of five years against principal and interest decides that principal and interest, with constant repayments of $2,875, works better for him. The useful part of that example is the pattern, not the figure: repayments stay broadly level while the balance declines.
Interest-only. For a defined period you pay the interest charged and the balance does not reduce through repayments. MoneySmart states clearly that at the end of the interest-only period, the loan will change to a "principal and interest" loan. MoneySmart also notes that the interest rate could be higher than on a principal and interest loan — a point worth pricing before you choose it rather than after.
Offset. MoneySmart's separate guidance explains how a mortgage offset account works, how it can reduce home loan interest, and whether it is worth having. In general terms, money held in an offset account reduces the portion of the loan that interest is calculated on, so less interest is charged while your cash stays accessible. Whether an offset is offered on a particular investment loan or product variant, and exactly how the lender calculates the offset benefit, are questions for the lender.
Cash flow now versus commitment later
Interest-only repayments are lower during the interest-only period, which frees cash in the early years of holding a property. The trade-off is that the balance does not fall, so the full amount still has to be repaid — just compressed into whatever term remains once the interest-only period ends.
Principal and interest costs more each month from the start, but the repayments do double duty: servicing the debt and reducing it. For an investor who wants equity to accumulate without having to decide to do anything, that forced reduction is the appeal.
Neither structure is automatically cheaper overall. Total cost depends on the rates that apply, how long you hold the property, the length of the interest-only period and what you do with any cash flow difference. Those inputs are lender-specific, so this guide does not put a number on the comparison — your lender can, for your actual loan.
The switch at the end of the interest-only period
This is the part that deserves the most attention before you sign, because it is predictable and yet frequently unplanned for. Per MoneySmart, the loan reverts to principal and interest at the end of the interest-only period. From that point, repayments must cover interest and clear the remaining balance over the remaining term — which means the monthly amount changes, and it changes regardless of whether your rental income has moved.
MoneySmart publishes tips to help borrowers manage the switch to principal and interest; it is worth reading that section before you commit to an interest-only period. Practical preparation looks like this:
- Diarise the expiry date well ahead of time, and ask the lender for the indicative repayment once the loan reverts, based on your current balance.
- Ask what rate applies after the revert, and compare it to the principal and interest rate you were offered at the start.
- Check whether you can make extra repayments during the interest-only period, and on what terms, if you want the balance lower before repayments step up.
- Do not build a plan that depends on refinancing before the switch. Refinance is an option you may or may not have when the time comes; the revertsion is a certainty written into the loan.
Where an offset fits
An offset is not a repayment type. It sits alongside either structure and changes the interest calculation. Because interest-only repayments reflect the interest charged, offsetting also reduces what you pay during the interest-only period; with principal and interest, the reduced interest means more of each level repayment goes to principal, so the balance falls faster.
Whether parking cash in an offset beats using that cash elsewhere depends on your circumstances, including your tax position. That comparison is outside this guide. Take it to a registered tax adviser and check the Australian Taxation Office's published guidance rather than relying on rules of thumb.
Comparing the three at a glance
| Principal and interest | Interest-only (during the period) | Offset account | |
|---|---|---|---|
| What repayments cover | Interest plus part of the balance | Interest charged over the period | No change to repayments; less interest is charged |
| Does the balance fall? | Yes, progressively | Not through repayments | Yes, when repayments stay level |
| Cash flow effect | Higher monthly commitment from the start | Lower commitment during the period | Depends on how much cash you keep there |
| What changes it | Falls to zero over the term if all repayments are made | Ends at the expiry of the period | Balance held, within product rules |
| Key thing to verify | Repayment amount and term | Expiry date, revert rate, post-revert repayment | Whether it is available on the loan, and how interest is calculated |
Questions to take to your lender
Bring these to the lender or broker and get the answers in writing before you commit:
- What interest rate applies during the interest-only period, and how does it compare with the principal and interest rate on the same loan?
- When exactly does the interest-only period end, and what will the repayment be at that point based on today's balance?
- Is an offset account available on this product, and is it available for the full term?
- Are extra repayments allowed during and after the interest-only period, and are there conditions attached?
- What fees or conditions apply to each option? Ask directly — do not assume they are the same across lenders.
Next steps
Start by deciding which of the three variables actually drives your decision: monthly cash flow, forced equity build, or flexibility around cash you intend to hold. Then get the lender's figures for both structures on your own numbers, including the post-revert repayment, and compare them side by side. If you want to read further on how loan structures and repayments are presented in the market, our home loan guides cover the mechanics in more detail at /money/home-loans/. If you would rather map your situation against lender criteria first, /match/ outlines how that works.
General information only
This article is general information about loan structures, not personalised legal, tax, credit or financial advice. Rates, fees, product features and eligibility differ between lenders and change over time; nothing here should be read as a recommendation of any provider or product, or as a prediction of any outcome, approval or saving. Tax treatment of investment loan interest and offset balances is not covered here — confirm it with a registered tax adviser and the Australian Taxation Office. Always read the credit guide, loan contract and product disclosure before committing, and seek independent advice about your own circumstances.