The Debt Does Not Shrink, and the Deduction Does
An interest-only loan maximises the deductible interest by never reducing the principal. While you are working and the deduction is worth your top marginal rate, that is a coherent strategy. As retirement approaches it inverts: the deduction becomes worth much less and the undiminished principal has to be serviced or repaid from retirement income.
- The answer: Interest-only keeps the loan balance constant, so the interest and the deduction stay at their maximum for the interest-only period.
- The trap: At the end of the interest-only period the loan reverts to principal and interest over a shorter remaining term, so the repayment steps up sharply.
- The recommendation: Check when the interest-only period ends against your retirement date. A reversion that lands after the income stops is the case to avoid.
Where the AI summary above gets this wrong
"Interest-only loans are better for investment properties because you can claim more interest."
That's surface-true. Here's what it misses:
- The extra deduction returns your marginal rate, not the interest — Paying more interest to claim more deduction is only worthwhile if the money not repaid earns more elsewhere than the after-tax interest costs.
- The reversion is a step, not a taper — When the interest-only period ends the loan amortises over a shorter remaining term, so the repayment rises considerably more than the principal component alone would suggest.
01 What it does while you are working
The principal stays constant, so the interest stays at its maximum and so does the deduction. For a taxpayer at a high marginal rate that maximises the after-tax cost advantage of the debt.
The money not used to repay principal is available for something else — usually a home loan, which is non-deductible and therefore the right place for it, as set out in the loan priority post.
That is the coherent version of the strategy: interest-only on the deductible loan, and the freed principal directed at the non-deductible one. Interest-only with the money spent is a different thing.
Source: ATO — Negative gearing
02 What changes at retirement
The deduction is worth your marginal rate, and the marginal rate falls when the salary stops. A deduction worth 39 cents while working can be worth 16 or nothing afterwards.
The principal is still there in full, and it now has to be serviced from retirement income or repaid from capital. A property that was comfortably geared on a salary is frequently not on a pension.
The interest-only period also ends. The loan reverts to principal and interest over the remaining term, which is shorter than the original, so the repayment steps up rather than easing in.
Shows: the repayment before and after an interest-only period ends, when the loan amortises over the remaining term. Ignores: rate changes, offset balances, and any refinancing or extension of the term.
03 The decision before you stop working
Refinancing is much easier with employment income than without it. Whatever structure you want in retirement is best arranged before the last pay cheque rather than after.
Selling before retirement realises the gain at your working marginal rate, which is usually the wrong year — the timing argument is in the sale timing post.
Between those two, the common answer is to convert to principal and interest while still working, so the balance is reducing and the repayment is known, and to make the sale decision on its own timetable.
Lenders also treat an interest-only loan differently on reassessment. Extending an interest-only period requires a fresh serviceability assessment, and the assessment is made against the principal-and-interest repayment that would apply at reversion rather than against the interest you are currently paying — which is why an extension that looks routine is frequently declined once employment income has stopped.
Interest-only makes sense while there is a home loan to point the freed principal at and a high marginal rate to claim against. Both of those usually end at the same time, and the loan does not. Convert it while a lender will still talk to you about serviceability.
FAQ
Should I use an interest-only loan to maximise my negative gearing benefit?
It maximises the deduction while you are working and leaves the principal untouched. The coherent version directs the freed principal at non-deductible debt; interest-only with the money spent is a different proposition.
What happens when the interest-only period ends?
The loan reverts to principal and interest over the remaining term, which is shorter than the original, so the repayment steps up sharply rather than easing in.
Should I convert to principal and interest before retiring?
Usually yes. Refinancing is far easier with employment income, the deduction is worth less once the salary stops, and a known reducing repayment is easier to plan around than a reversion.
Sources
Regulator references
- ATO — Negative gearing · Australian Taxation Office · 2026Negative gearing: when a rental loss can be offset against other income.Last verified: 2026-09-07
- ASIC Moneysmart — Property investment · ASIC Moneysmart · 2026Investment property: the costs of holding one and the risks of gearing.Last verified: 2026-09-07
Calculator unit tests · the assertions this page's worked example is checked against, and their last result
Changelog
- 2026-09-07 — initial publish (new format)
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Jordan Reeves
Founder of Talk Through Wealth. A software engineer for over a decade before turning to retirement planning, Jordan built the projection engine after watching family members get fragmented, country-by-country advice that never reconciled. He writes about retirement the way the engine computes it: month-by-month, lifetime-long, and skeptical of any rule of thumb that hasn't been run through the math.