Changing Investment Loan Repayments: What Actually Changes For Tax

Changing your investment loan from interest‑only (IO) to principal‑and‑interest (P&I), or upping repayments, usually doesn’t change what’s deductible today.

For the ATO, the core rule is: interest is deductible to the extent the borrowed money is used to produce assessable income, not whether you pay IO vs P&I or how fast you pay it down.

Where people get hurt is when they change how they use the loan – redraws, offsets, and messy splits.

Keeping investment loans clean and using offsets avoids ATO headaches when you change repayments.

What the ATO actually cares about (not your repayment type)

From a tax perspective, three things matter:

1. Purpose of the borrowing – what the funds were used for.
2. Tracing – whether you can show that purpose clearly.
3. Changes of use – redraws, refinances, or mixed private/investment use.

Whether you pay IO or P&I is mostly irrelevant to deductibility.

If the entire loan funded an investment property deposit and costs, the interest on that balance is generally deductible. If part of it funded a car or holiday, that part is not.

This is why keeping separate loan splits for each purpose is so powerful. It aligns with the principle that purpose, not security, drives deductibility (see also /insights/using-equity-release-next-investment-without-breaking-ato-rules).

IO vs P&I: does switching change your deduction?

On its own, no.

• Interest portion: stays deductible to the extent the loan is investment‑purpose.
• Principal portion: never deductible – it’s just returning capital.

Change from IO to P&I and you usually:

• Pay less interest each year over time (so smaller deductions).
• Build equity faster.

That’s a cashflow and strategy decision, not a tax win or loss. If you’re weighing up timing, see how this article connects to /insights/refinance-investment-loan-interest-only-to-principal-and-interest.