When to Use Interest Only vs Principal and Interest

Interest Only vs Principal and Interest: The Core Trade-Off

An interest-only loan lets your SMSF pay only the interest component each month, preserving capital but deferring equity build-up. A principal and interest loan amortises the debt over the term, building equity in the property but requiring larger repayments.

Consider a magistrate whose SMSF holds a warehouse leased back to their legal consultancy business. The SMSF entered into a limited recourse borrowing arrangement to acquire the property in March, and the trustee is deciding between a five-year interest-only period followed by principal and interest repayments, or principal and interest from day one. At current variable rates on a $600,000 SMSF commercial loan, the interest-only repayment might sit around $3,000 per month, while principal and interest over 25 years would be closer to $3,600. The $600-per-month difference accumulates: over five years, interest-only preserves roughly $36,000 in liquidity within the fund, which can be directed to contributions, other investments, or held as a buffer. The downside is that when the interest-only period expires, the principal and interest repayment increases sharply because the remaining loan term is shorter and the principal hasn't been reduced.

When Magistrates Choose Interest Only for SMSF Commercial Loans

Interest-only repayments suit SMSFs that prioritise liquidity or expect stronger investment returns outside the property itself.

In a scenario where a magistrate is five years from retirement and plans to wind down contributions while maintaining current pension reserves, an interest-only structure allows the SMSF to lease a commercial premises to a related party business while preserving cash flow for pension payments once the fund transitions to pension phase. Because the property is business real property and leased to a related party, the SMSF's interest in the holding trust is not an in-house asset. The interest-only loan allows the SMSF to meet minimum pension obligations without forced asset sales. Rental income covers the interest cost, and the SMSF trustee plans to sell the property or refinance to principal and interest once pension phase begins and the member's cash flow stabilises.

Interest-only loans also make sense where the SMSF is holding commercial property as a long-term accumulation asset and the member is still contributing at or near the concessional cap. The saved repayment amount can be allocated to other holdings or to bolster liquidity while the property appreciates. The catch is that you're not reducing the loan balance, so the outstanding debt remains constant and the loan term doesn't shorten unless you make voluntary principal repayments.

Principal and Interest Repayments: Building Equity in Accumulation Phase

A principal and interest loan reduces the balance each month, building unencumbered equity in the commercial premises.

For an SMSF that holds a medical consulting suite or office premises leased at arm's length to an unrelated tenant, principal and interest repayments over 20 to 25 years align with a long-term hold strategy. Each repayment increases the fund's equity, which can be realised on sale or refinanced later to fund other acquisitions. This structure reduces interest cost over the life of the loan because the principal balance falls steadily. It also removes refinancing risk: if the member plans to transition the SMSF to pension phase within ten years, paying down principal now means the loan balance is lower when that transition occurs, reducing the risk that pension-phase income won't cover repayments if rental income drops or the property is vacant.

Principal and interest loans suit SMSFs where the member has stable income, expects to retire with the property still held, and wants to minimise debt in pension phase. The higher repayment is a constraint, but it forces discipline and ensures the fund isn't carrying a large loan balance when the member's capacity to contribute winds down.

Tax Treatment of Interest Costs in Accumulation and Pension Phase

Interest on an SMSF commercial loan is deductible against the fund's assessable income in accumulation phase, and ignored under the exempt current pension income rules in pension phase.

When the SMSF is in accumulation phase, rental income and any net capital gain are taxed at 15 per cent, and interest expense is deductible. If the property generates $40,000 in annual rent and the interest cost is $30,000, the SMSF pays tax on $10,000 at 15 per cent, resulting in a $1,500 liability before any other deductions. Once the SMSF transitions to pension phase and the property supports a retirement phase income stream, income from that asset is exempt under the exempt current pension income rules, and the interest deduction is no longer relevant because there's no assessable income to offset. The repayment structure doesn't change the tax outcome in pension phase, but it does in accumulation: higher interest-only payments deliver a larger deduction, which reduces the fund's tax liability while the loan balance remains constant.

This is one reason magistrates with SMSFs in accumulation phase sometimes prefer interest-only structures in the early years: the full interest cost is deductible, and the fund retains liquidity to make further concessional contributions or rebalance the portfolio. Once pension phase begins, the interest deduction disappears, and the focus shifts to cash flow and debt reduction.

What Happens When the Interest-Only Period Ends

When an interest-only period expires, the loan reverts to principal and interest repayments over the remaining term, and the repayment amount increases.

If a magistrate's SMSF has a $500,000 loan with a five-year interest-only period and a 25-year total term, the principal and interest repayment after year five is calculated over the remaining 20 years, not 25. The monthly cost jumps because the principal hasn't been reduced and the amortisation window is shorter. At that point the SMSF trustee can refinance to extend the term, switch lenders, or accept the higher repayment. Refinancing an LRBA entered into before 10 August 2026 does not require the property to be business real property, but refinancing an LRBA entered into on or after that date does. If the property stops being business real property during the life of an LRBA entered into from 10 August 2026, the SMSF breaches the borrowing prohibition and compliance action may follow.

The risk with interest-only structures is that members underestimate the repayment increase when the interest-only period ends, or assume they'll refinance without considering whether the property still meets the business real property definition or whether the SMSF's circumstances have changed. Planning the exit from interest-only at the time you enter the loan avoids this.

Matching Loan Structure to Retirement Timeline

The right structure depends on how far the member is from pension phase, the stability of the rental income, and whether the SMSF will hold or sell the property in retirement.

A magistrate within five years of retirement might choose interest-only to preserve liquidity, knowing the SMSF will either sell the commercial premises when pension phase begins or refinance at that point if holding the asset suits the fund's long-term strategy. A magistrate with 15 years to retirement and stable rental income from a related party lease might choose principal and interest from the outset, building equity while contributions continue and ensuring the loan balance is manageable when contributions taper. There's no universal answer, but the structure should reflect the member's contribution capacity, the SMSF's income, and the intended hold period for the property. Misalignment between loan structure and retirement timeline creates liquidity pressure or leaves the fund holding more debt than it can service once pension payments begin.

Split Loans: Combining Both Structures

Some lenders allow the SMSF to split the loan into an interest-only portion and a principal and interest portion, giving partial flexibility without full exposure to either structure.

A $600,000 SMSF commercial loan might be split into $400,000 interest-only for five years and $200,000 principal and interest over 25 years. The SMSF pays down part of the debt immediately while retaining liquidity on the larger portion. This can suit magistrates who want to reduce the loan balance before pension phase but don't want the full repayment burden of a principal and interest loan across the entire debt. The mechanics depend on the lender: some treat the split as two separate facilities under the same LRBA, others structure it as a single facility with blended terms. Either way, the SMSF trustee must ensure the arrangement complies with the LRBA conditions, including the single-asset requirement and the limitation on drawdowns for capital improvements.

Fixed or Variable Rates on Interest-Only and Principal and Interest Loans

Whether the loan is interest-only or principal and interest, the SMSF trustee must also decide between fixed and variable rates.

Fixed rates lock the interest cost for a period, typically one to five years, which stabilises repayments and protects the SMSF from rate rises during that window. Variable rates move with the market, which can reduce the interest cost if rates fall but increases repayments if they rise. On an interest-only loan, a fixed rate removes repayment uncertainty during the interest-only period, but the SMSF still faces refinancing or reversion risk when the fixed term expires. On a principal and interest loan, fixing the rate provides repayment certainty and allows the trustee to model the fund's cash flow over the fixed period. Some lenders offer split rate structures, where part of the loan is fixed and part is variable, which balances certainty with flexibility. The trade-off is between control and cost: fixed rates tend to price in an expectation of future rate rises, while variable rates reflect the current market and allow the SMSF to make extra repayments without penalty. For more on how different loan structures interact with rate decisions, refer to our page on interest only loans for lawyers.

Refinancing Between Interest Only and Principal and Interest

An SMSF can refinance an existing LRBA to change the repayment structure, subject to lender appetite and the business real property requirement for LRBAs entered into from 10 August 2026.

A magistrate whose SMSF entered into an interest-only LRBA in June 2026 over a mixed-use property that included a small residential component may later want to refinance to principal and interest. Because that LRBA was entered into before 10 August 2026, the property does not need to be business real property when the SMSF refinances. However, if the SMSF entered into the LRBA in September 2026 over a property that was business real property at the time, any refinance must occur while the property still meets that definition. If the property stops being business real property, the SMSF cannot maintain or refinance the LRBA without breaching the borrowing prohibition. This is particularly relevant for magistrates whose SMSFs hold commercial premises that may later be converted to residential use or left vacant without active plans to re-lease. The refinancing decision should be made with advice from both a mortgage broker experienced in SMSF lending and the fund's accountant or administrator, to confirm the property still qualifies and the refinance terms comply with the LRBA conditions.

Related Party Loans and Arm's Length Terms

Where the SMSF borrows from a related party, the loan terms must be on arm's length conditions, regardless of whether the loan is interest-only or principal and interest.

Practical Compliance Guideline 2016/5 sets out the ATO's view on arm's length terms for related party LRBAs, including acceptable interest rates, security, and documentation. A related party lender must charge no more than an arm's length rate, and income derived from non-arm's length terms is taxed as non-arm's length income at 45 per cent. For magistrates whose SMSFs borrow from family members or entities they control, this means the loan must be documented with a written agreement, interest must be charged and paid, and repayments must be made on time. Interest-only terms are acceptable provided they reflect commercial lending standards, but indefinite interest-only periods or artificially low rates will attract scrutiny. Principal and interest loans from related parties must also meet the guideline's requirements. The risk of non-compliance is immediate and material: non-arm's length income is taxed at the top marginal rate, which erodes the tax benefit of holding the asset in the SMSF. For context on how SMSF structures fit within broader strategies, see our page on SMSF loans for lawyers.

Loan Structure and Capital Gains Tax on Sale

The loan structure does not directly affect the capital gains tax outcome, but it influences the SMSF's equity position and liquidity at the time of sale.

If a magistrate's SMSF sells a commercial property in accumulation phase after holding it for more than 12 months, the net capital gain is taxed at an effective rate of 10 per cent after applying the one-third CGT discount. If the property was held for less than 12 months, the full gain is taxed at 15 per cent. The loan structure affects how much net equity the SMSF realises: an interest-only loan means the full loan balance is still outstanding at sale, while a principal and interest loan over the same period means the balance has been reduced. On a $600,000 loan held for five years on an interest-only basis, the SMSF still owes $600,000 at sale. On a principal and interest basis over 25 years, the balance after five years might be around $530,000, giving the SMSF an extra $70,000 in net equity. If the property is a segregated current pension asset at the time of sale, the capital gain is exempt and the loan structure is irrelevant to the tax outcome, though it still affects the cash the SMSF receives. For magistrates planning to sell commercial premises within a defined timeframe, modelling the net equity outcome under each structure helps clarify whether the liquidity preserved by interest-only justifies the higher outstanding balance at sale.

Call one of our team or book an appointment at a time that works for you. We work with magistrates and judicial officers regularly and can compare SMSF commercial lenders, model repayment scenarios, and structure the loan to suit your fund's income, retirement timeline, and property strategy.

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