Prepay Investment Loan Interest Before 30 June 2026 — The 12-Month Rule (ATO)
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Primary tax-year context: 2025-26
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General information only. This is not tax or financial advice. Consult a licensed financial adviser or registered tax agent for advice specific to your situation.
With the RBA cash rate at 4.10% through April 2026 and most investor variable rates sitting between 6.3% and 6.9%, a single 12-month interest prepayment before 30 June is one of the largest legal deductions an individual property investor can pull forward into the 2025-26 income year. The rule that enables this is ITAA 1936 s 82KZM — the “12-month rule” for prepaid expenditure by non-business individuals — and it’s been stable for more than two decades.
This article walks through the eligibility test, a worked example on a $600,000 investment loan, the five scenarios where prepaying backfires, and what to do if the bank’s fixed-rate interest-in-advance product isn’t available on your loan.
What the 12-Month Rule Actually Says
Under ITAA 1936 s 82KZM, an individual (acting in a non-business capacity — this includes rental property investors and share investors using a margin loan) can claim an immediate deduction for a prepayment if both of these are true:
- The eligible service period is 12 months or less; and
- The service period ends no later than the last day of the income year following the one in which the payment was made.
For a payment made on 15 June 2026, the allowable service period can run up to 14 June 2027 (12 months) — well within the outer boundary of 30 June 2027. For a payment made on 1 April 2026, the service period can run up to 31 March 2027 — also within limits. The test is about the service period, not the calendar year.
If you prepay more than 12 months of interest in one hit — say 18 months — s 82KZMA requires you to apportion the excess over the full service period. Most lenders only offer 12-month prepayment anyway, so this rarely bites in practice, but don’t assume “I’ll just prepay 2 years and double the deduction.” The legislation specifically closed that loophole in 1999.
For business taxpayers (including property investors operating through a company, trust, or as a genuine business — which is rare for residential rental — separate rules apply under s 82KZMD and s 82KZMF. This article focuses on the individual investor case.)
The Mechanics at Your Lender
Most major lenders offer an “interest in advance” or “prepay interest” facility on fixed-rate investment loans. Variable-rate loans generally do not allow true prepayment — the best you can do is prepay on a fixed-rate product, which usually requires locking in the rate for the prepaid period.
Typical structure with the big four:
| Lender | Product | Minimum fixed term | Rate premium vs standard fixed |
|---|---|---|---|
| CBA | Fixed-rate Investor IO with prepayment | 1 year | ~0.10–0.20% discount (lender keeps interest) |
| Westpac | Fixed-rate Investor IO | 1 year | similar |
| ANZ | Fixed-rate Investor with interest in advance | 1 year | similar |
| NAB | Fixed-rate Investor IO annual prepayment | 1 year | similar |
Practical steps:
- Contact your lender at least 3–4 weeks before 30 June. Prepayment applications take time and the June queue is busy.
- Lender switches the loan to a 12-month fixed rate.
- You pay the full 12 months of interest up-front. The loan balance is not reduced — you’re paying interest only.
- Lender issues a statement showing the prepayment date, amount, and eligible service period.
- Keep that statement. You’ll need it at tax time and if the ATO queries the deduction.
Note that the prepaid amount must actually hit the lender’s account by 30 June 2026. BPAY and direct debit typically take 1–3 business days. Send the payment by 25 June to be safe.
Worked Example — Nadia’s $600,000 Investor Loan
Nadia owns a Melbourne investment unit with a $600,000 interest-only loan at 6.50% variable. On 1 June 2026 she contacts Westpac and asks to switch to a 12-month fixed-rate prepay product.
Westpac’s prepayment fixed rate is 6.40% for the year beginning 15 June 2026. Nadia pays the full 12 months of interest on that date.
- Interest prepaid: $600,000 × 6.40% = $38,400
- Eligible service period: 15 June 2026 to 14 June 2027
- Test: period ≤ 12 months ✓; ends before 30 June 2027 ✓ → fully deductible in 2025-26
Her 2025-26 rental property deductions look like this:
| Item | Amount |
|---|---|
| Interest (prepaid) | $38,400 |
| Council rates, insurance, agent fees | $6,200 |
| Depreciation and capital works | $8,000 |
| Total deductions | $52,600 |
| Rental income received | $32,000 |
| Net rental loss | $20,600 |
That $20,600 net loss offsets Nadia’s salary income. She earns $155,000 before the property loss, putting her in the 37% bracket + 2% Medicare levy = 39% effective marginal rate.
Tax benefit of the prepayment:
- Without prepayment (pay monthly): she’d deduct ~6.5 months of interest in 2025-26 (say $18,200, since she bought mid-year) — marginal saving $7,100.
- With 12-month prepayment: she deducts $38,400 in 2025-26 — marginal saving $14,980.
- Cash flow benefit this year: ~$7,880 extra refund.
Model your own numbers on the prepaid deductions calculator or the full investment property calculator.
Important next-year consequence: In 2026-27, Nadia has zero deductible interest on this loan for the first 11.5 months (she’s already claimed it). Her rental income that year is fully taxable until the June 2027 re-prepayment. If she doesn’t prepay again, 2026-27 looks very different from 2025-26 on paper — the ATO doesn’t care, but her tax agent needs to model the cliff.
Five Scenarios Where Prepaying Backfires
The 12-month rule is legal and clean — the traps are all about timing and forecasting.
Trap 1 — You expect income to fall next year.
If you’re planning parental leave, a sabbatical, retirement, or a step-down role for 2026-27, prepaying now pulls the deduction into a higher-marginal-rate year — which sounds good, until you realise you’re also giving up the deduction from a year where your marginal rate might already be lower. This is almost always still a win (tax paid sooner deducted sooner), but the marginal rate differential narrows the benefit.
Worked delta: If your rate is 37% this year and 32.5% next year, $38,400 × (37% – 32.5%) = $1,728 incremental benefit from the timing shift. Meaningful but not huge.
Trap 2 — You expect income to jump next year.
The mirror image. If you’re due a big promotion, a windfall (CGT event, ESS vesting, inheritance) in 2026-27, you’re shifting the deduction from a higher-rate year to a lower-rate year — the opposite of what you want. Run the numbers with next year’s expected marginal rate before committing.
Trap 3 — You might sell or refinance mid-period.
The eligible service period runs forward from the payment date. If you sell the property on 1 December 2026 — halfway through the service period — the remaining prepaid interest from 1 December to 14 June 2027 covers a period when you no longer own an income-producing asset. The ATO’s position is that the remaining prepayment is not deductible and may need to be written back into the 2025-26 claim (via an amendment) or, more commonly, included as a capital cost adjustment to the property’s cost base.
Refinancing is more forgiving — if you discharge the loan and replace it with another loan for the same property, the early-termination fee is deductible under ITAA 1997 s 25-30 (borrowing expenses) and the remaining prepayment is usually pro-rated against the termination settlement. But bank-by-bank practice varies.
Trap 4 — Cashflow consumed by the prepayment.
$38,400 out of your offset account on 15 June is $38,400 that stops earning offset-equivalent 6.40% for the next 12 months. The “lost offset interest” is roughly $1,200 (half-year average × rate). Small but not zero. If the cash came from a line of credit or redraw, you’re also paying interest on that money, which partially defeats the purpose.
Trap 5 — Missing the 30 June cut-off by settlement lag.
BPAY to the lender on 29 June 2026 at 4pm may settle on 2 July 2026. The ATO treats the payment as made when the lender actually receives it. If settlement slips into July, the entire deduction moves to 2026-27. Always pay by 25 June for BPAY and 28 June for direct bank transfer to be safe.
What You Can’t Prepay
The 12-month rule does not apply to everything. Specifically excluded:
- Principal repayments — these are never deductible; prepaying them just reduces your loan balance.
- Council rates, water, insurance prepaid for more than 12 months — same rule, same logic.
- Body corporate levies paid as a lump-sum capital contribution — capital, not deductible (though normal annual levies are deductible in the year incurred).
- Prepaid rent (if you’re a tenant, not the landlord) for a period > 12 months — beyond the scope of residential property investing.
- Tax agent fees prepaid — deductible, but only for the service period you’ve paid for (usually just the next return).
Frequently asked questions
Q: Can I prepay only 6 months of interest instead of 12?
Yes. The 12-month rule is a ceiling, not a floor. A 6-month prepayment is still fully deductible in the year of payment, provided the service period ends within the next income year. Some investors do this to smooth cashflow.
Q: What if my loan is a line of credit or offset account, not a traditional loan?
Interest on line-of-credit products is typically not prepayable because there’s no fixed period of advance — you’re charged interest on drawn balance as you draw it. You can’t prepay something that hasn’t been incurred yet. Offset accounts just reduce interest charged; there’s nothing to prepay there either.
Q: Does the 12-month rule apply to margin loan interest on shares?
Yes — the rule applies to any prepayment by an individual in a non-business capacity, including interest on margin loans, protected equity loans, and internally-geared share products. Check with the lender that the product allows prepayment.
Q: I prepaid interest last year and want to prepay again this year. Is there a risk?
No, prepaying in consecutive years is legal and common. The only risk is that you’ve now “used up” the timing benefit — each year’s prepayment merely replaces last year’s, giving you no net cashflow advantage after year one. The deduction pattern is level.
Q: What if my marginal rate changes between the payment date and 30 June?
The deduction is claimed in the income year of payment regardless of when in that year you paid. Your effective saving is based on your marginal rate for the full year, not the rate on the payment date.
Q: Can I prepay and then claim capital works (Division 43) on the same property in the same year?
Yes — Division 43 capital works deduction is separate from Division 8 general deduction (interest). Most investors claim both in the same year. They stack.
Sources
- ATO — Prepaid expenses
- ATO — Rental properties 2024-25 (Section 11: Prepaid expenses)
- Income Tax Assessment Act 1936, ss 82KZM (12-month rule), 82KZMA (apportionment)
- ATO — Guide to depreciating assets 2024-25
- RBA — Cash rate target (April 2026)
Ready to prepay? Model it first
Run your loan balance, fixed rate, and marginal tax rate through the prepaid deductions calculator to confirm the cash flow and tax impact. Then compare the lifetime outcome with the investment property calculator or the interest-only vs principal-and-interest scenario. Call your lender by 5 June to be certain the prepayment application clears before 30 June.
See how this lever ranks against your other 30-June moves: EOFY Action Plan.