Optimising Your Investment Loan and Portfolio Structure

When Loan Structure Matters More Than Rate

You can refinance for a lower rate and still come out behind if your loan structure doesn't support the portfolio you're building. Prosthodontists frequently move from a single property to multiple holdings, and the way you structure borrowing, offset accounts and repayment features determines how much equity you can access, how you manage cashflow across properties, and whether your lending supports the next purchase or constrains it.

Consider a prosthodontist who purchased an investment property on a principal-and-interest loan with all surplus income directed to additional repayments. Four years later, the property had appreciated and the balance had reduced by $80,000. When they applied to purchase a second property, the lender recalculated their servicing based on a new debt-to-income ratio above six, and the smaller portfolio balance meant less usable equity after the serviceability buffer was applied. The loan wasn't structured to preserve flexibility, and the lower balance created a borrowing constraint rather than an advantage.

Optimisation isn't about taking on more debt. It's about aligning loan features, repayment structure and equity access with the portfolio you're building and the income you're earning.

Interest-Only Periods and When They Work

Interest-only repayments reduce your monthly outgoing and increase borrowing capacity for additional properties. An interest-only period is typically available for one to five years on investment loans, with the ability to extend subject to lender approval and loan performance.

Interest-only works where you're actively building a portfolio and need maximum serviceability for the next purchase, or where rental income doesn't cover principal-and-interest repayments without regular top-ups. It also works where you're directing surplus income into offset accounts rather than reducing the loan balance, which preserves access to funds and maintains deductible debt.

Principal-and-interest repayments reduce your total debt and increase your equity position, but they also lock capital into the property. Once a repayment is made, you can't access those funds without refinancing or applying for a new facility. For a prosthodontist with variable income from both employment and private practice work, maintaining liquidity through offset rather than principal reduction provides flexibility during periods of lower billing or planned leave.

Offset Accounts Across Multiple Properties

An offset account linked to your investment loan reduces the interest charged each month without reducing your deductible debt. The balance in the offset account is subtracted from the loan balance when calculating interest, so a $500,000 loan with $50,000 in offset is charged interest on $450,000.

Where you hold multiple investment properties, you want separate loan accounts with separate offset facilities for each property. This allows you to direct rental income, surplus salary or practice distributions to specific offsets depending on which loan carries the highest rate or which property you intend to sell or refinance first.

A common setup involves an interest-only loan on each investment property with a linked offset, and rental income deposited directly into the offset account for that property. You pay interest only on the gap between the loan balance and the offset balance, and the full loan amount remains deductible. If you need funds for a deposit on another property, you can withdraw from the offset without triggering a redraw or affecting your deductibility.

Some lenders allow multiple offset accounts linked to a single loan split, which can be useful where you're managing funds across different purposes or separating rental income from operating income. Not all lenders offer this feature, and it's often only available on specific loan products, so it should be confirmed during the application.

Debt-to-Income Limits and Portfolio Lending

From February 2026, lenders can approve no more than 20 per cent of new investor loans to borrowers with a total debt-to-income ratio of six times or greater. This limit applies separately to each lender's investor lending book and is measured quarterly.

For a prosthodontist earning $250,000 annually, the threshold is $1.5 million in total debt across all home loans. Beyond that level, you're competing for a place within the lender's 20 per cent allocation, and approval depends on the lender's position within their quarterly limit at the time you apply.

Where your total borrowing approaches or exceeds six times income, loan structure becomes particularly relevant. Lenders assess serviceability at the loan product rate plus a 3 per cent buffer, so an interest-only loan at 6.3 per cent is assessed at 9.3 per cent. Offset balances reduce interest costs but don't reduce the assessed loan balance. Rental income is included in serviceability calculations, but most lenders apply a discount of 20 per cent to account for vacancy, management fees and maintenance.

If you're planning to hold multiple properties, structuring loans to maximise assessed income and minimise assessed expenses improves your serviceability position and keeps you within the debt-to-income threshold for longer. This might involve consolidating non-deductible debt, switching to interest-only on investment loans, or timing purchases to align with higher income years.

Splitting Loans Between Fixed and Variable

A split loan divides your borrowing into two or more accounts, each with separate terms. One split might be fixed for three years at a lower rate, while the other remains variable with full offset and redraw.

Splitting allows you to lock in a portion of your borrowing while retaining flexibility on the rest. Fixed-rate splits don't typically allow offset accounts or additional repayments beyond a small annual threshold, so the variable split carries the offset facility and absorbs any surplus cashflow.

For investment loans, a 50/50 split between fixed and variable is common, though the ratio depends on your cashflow, portfolio plans and view on rate movements. The fixed split provides certainty on a portion of your repayments, and the variable split allows you to pay down debt or build offset without penalty.

Break costs apply if you repay or refinance a fixed-rate loan before the fixed period ends. The break cost is calculated based on the difference between your fixed rate and the lender's current cost of funds for the remaining fixed period. Where you're planning to sell or refinance an investment loan within two to three years, a variable-only structure or a small fixed split reduces the risk of incurring break costs.

Equity Release and Cross-Collateralisation

Equity in an existing property can be used as security for a deposit on the next investment. Lenders will typically allow you to borrow up to 80 per cent of the property's value without paying Lenders Mortgage Insurance, so a property worth $800,000 with a $400,000 loan provides access to $240,000 in usable equity.

Cross-collateralisation occurs where a lender takes security over multiple properties under a single loan facility. This can simplify the application process and reduce legal costs, but it also means you can't sell or refinance one property without the lender's consent to release that security.

Where possible, you want each property held under a separate loan facility with separate security. This structure allows you to sell, refinance or restructure individual properties without affecting the others. Some lenders will only lend on a cross-collateralised basis, particularly where you're accessing equity from one property to fund another. In those cases, the trade-off is between accepting cross-collateralisation or moving to a different lender.

Tax Deductibility and Loan Purpose

Interest on an investment loan is deductible where the borrowing is used to purchase or hold an income-producing property. Interest on borrowing for private purposes, including your own home, is not deductible regardless of the security provided.

If you refinance an investment loan and increase the balance to fund renovations on that investment property, the additional interest remains deductible. If you increase the balance to fund a holiday, a car, or renovations on your own home, the interest on that additional amount is not deductible, even though the security is an investment property.

Where you're accessing equity from an investment property to fund a deposit on another investment property, the interest on the equity loan is deductible because the funds are being used for investment purposes. The key is maintaining a clear link between the borrowed funds and their use. Mixing purposes within a single loan account makes it difficult to separate deductible from non-deductible interest, so separate loan splits or separate facilities are preferable.

From the 2027-28 income year, losses on established residential investment properties acquired after 12 May 2026 can only be offset against income from other residential properties, not against salary or practice income. Properties acquired before that date, and new builds acquired after that date, remain fully deductible under the existing rules. This affects cashflow planning for future acquisitions but doesn't change the deductibility of interest itself.

Structuring for the Portfolio You're Building

A single investment property can sit comfortably on a standard loan with minimal optimisation. Once you're holding two or more properties, or planning to purchase additional properties over the next few years, loan structure determines how much you can borrow, how quickly you can access equity, and how you manage cashflow across the portfolio.

You want separate loan facilities for each property, offset accounts linked to each loan, and the ability to split between fixed and variable within each facility. You want interest-only repayments where serviceability is tight or where you're preserving equity for the next purchase. You want clear separation between deductible and non-deductible debt, and you want loan features that allow you to deposit and withdraw funds without affecting deductibility or triggering redraw restrictions.

Not all lenders offer all of these features, and the lenders who do often reserve them for specific loan products or borrower profiles. Prosthodontists with stable income and strong serviceability typically have access to a wider range of loan products, but that access depends on applying with the right lender and structuring the application correctly from the outset.

Call one of our team or book an appointment at a time that works for you.

Frequently Asked Questions