Interest Only vs Principal and Interest: Which Loan Is Right for Your Investment Property?
A man looking at a percentage symbol, choosing between interest only or principal and interest.
One of the most common questions we get from investors is about loan structure.
Should I go interest only or principal and interest?
Most people default to whatever their bank recommends. Most banks push principal and interest because it reduces their risk. But what reduces the bank's risk is not always what is best for your investment strategy.
Here is a clear breakdown of both options so you can make an informed decision.
What Is the Difference?
Every mortgage repayment has two components: the interest charged on the loan balance and the principal, which is the actual loan amount itself.
Principal and interest: You repay both components with every repayment. The loan balance reduces over time.
Interest only: You repay only the interest component for a defined period, typically one to five years. The principal balance stays the same during this time.
The practical difference is your monthly cashflow. On a $600,000 investment loan at 6%, the difference between the two structures is approximately $600 to $700 per month.
That is real money that either stays in your pocket or goes toward reducing the loan balance.
How Does This Affect Your Tax Position?
This is where most investors miss something important.
Interest on an investment loan is tax deductible. Principal repayments are not.
Under interest only, your entire repayment is interest and therefore your entire repayment is deductible. That deductible amount stays consistent throughout the interest only period.
Under principal and interest, only the interest portion is deductible. As the loan balance reduces, that deductible amount shrinks each year.
For a high-income earner at the top marginal tax rate of 47%, every dollar of deductible interest saves 47 cents in tax. Keeping that deduction as high as possible during the accumulation phase is a meaningful advantage.
The Argument for Interest Only
For investors building a portfolio across multiple properties, cashflow is everything.
Lower repayments under interest only free up money that can be directed toward your next deposit, your cash buffer, or your home loan. This keeps momentum in the portfolio-building phase without stretching your serviceability too thin.
There is also a common misconception worth clearing up.
Interest only does not mean you are not building equity. Capital growth continues regardless of your repayment structure. A $600,000 property growing at 7% per year adds $42,000 in equity through growth alone in year one. The market is doing most of the equity work.
The Argument for Principal and Interest
Principal and interest reduces your loan balance faster and builds equity through repayments rather than relying solely on capital growth.
For investors who want their portfolio fully unencumbered by retirement, P&I loans reduce the total interest paid over the life of the loan and bring the balance down steadily over time.
It is also worth noting that as the balance reduces, your minimum repayment decreases. This can improve your serviceability position when applying for future loans.
The Home Loan vs Investment Loan Distinction
This is where many investors make a costly mistake.
The interest on your home loan is not tax deductible. It is non-deductible debt that costs you every dollar of repayment with no tax offset.
The interest on your investment loan is fully deductible.
The most mathematically efficient structure for most investors who hold both is to direct surplus cashflow toward the non-deductible home loan while keeping the investment loan on interest only.
You are paying down your most expensive debt first while preserving the tax efficiency of your investment loan. Investors who structure both loans the same way without considering deductibility are leaving real money on the table every year.
So Which One Is Right for You?
Interest only tends to suit:
Investors in the accumulation phase building a portfolio across multiple properties
High-income earners who benefit significantly from deductible interest
Investors who also hold a non-deductible home loan and want to pay that down faster
Principal and interest tends to suit:
Investors who have paid off their home loan and have no non-deductible debt to prioritise
Investors in the later stages of their portfolio journey focused on reducing debt ahead of retirement
Those who prioritise the certainty of a reducing loan balance over maximising cashflow
Neither structure is universally right. The correct answer depends on where you are in your investment journey, your income, your tax position, and how your overall strategy is structured.
What Most Investors Get Wrong
Treating the investment loan the same as the home loan
These are fundamentally different products from a tax perspective. The instinct to pay everything down as quickly as possible is sensible for non-deductible debt and potentially counterproductive for deductible debt.
Choosing P&I to feel responsible
Reducing debt feels good. But directing cashflow toward investment loan principal during the accumulation phase can slow your portfolio-building process significantly.
Not reviewing the structure regularly
The right structure at the start of your journey may not be right five years in. As your situation changes, your loan structure should be reviewed alongside it.
The Bottom Line
Loan structure is not a detail. It is one of the most consequential finance decisions in your portfolio and one of the easiest to get wrong without realising it.
If you are unsure which structure suits your situation, the answer is not to guess. It is to sit down with a finance specialist who understands investment lending and who has looked at your full picture before making a recommendation.
Want to understand which loan structure is right for your portfolio? Talk to the Motivate Finance team today.