Key Takeaways
- Principal and interest (P&I) and interest-only (IO) are the two primary repayment structures for commercial loans in Australia, and they produce materially different outcomes across cash flow, total cost, equity, tax, and lender assessment.
- P&I produces higher regular repayments, lower total interest cost, steady equity build, and broader lender support; IO produces lower regular repayments during the IO period, higher total interest over the loan’s life, deferred equity build, and tighter lender restrictions.
- Tax treatment can differ between the two: for investment property, interest is deductible under both structures, but the proportion of each repayment that is deductible differs significantly.
- Neither structure is universally better; the right choice depends on the borrower’s cash flow priorities, equity-building goals, holding period, and the lender’s current appetite for IO lending.
Two Structures, Five Comparison Dimensions
Commercial borrowers in Australia choose between two primary repayment structures: principal and interest (P&I), where each repayment reduces both the interest charge and the loan balance, or interest-only (IO), where the borrower pays only the interest charge during an agreed period while the principal stays constant. The choice between them shapes the loan’s behaviour across the borrower’s holding period in ways that go well beyond the headline repayment number.
This article compares the two structures across five dimensions that matter to commercial borrowers: cash flow, risk, tax treatment, equity-building, and lender approval. The aim is a clear side-by-side reference, not a recommendation in either direction. Hence, both structures are presented under each heading with their respective trade-offs, and the worked example numbers below show the same loan modelled under each scenario.
This guide sets out the practical differences between P&I and IO commercial loans for borrowers comparing the two structures on a specific deal. If you want to model both options against your actual situation, the Loanworx commercial broking team can run the numbers alongside current lender appetite for IO availability.
The Worked Example Both Structures Are Compared Against
To anchor the comparison in concrete numbers, the figures below use a $750,000 commercial property loan at 6.5% over 20 years. This is a reasonably typical commercial property scenario, large enough to show meaningful differences and structured to keep the arithmetic readable.
Under Principal and Interest
On full P&I from the start, the loan repays $750,000 of principal and the associated interest evenly across 240 monthly repayments. The regular monthly repayment is approximately $5,594. Over the full 20-year term, the borrower pays approximately $1,343,000 in total, of which $593,000 is interest. The loan balance reduces from $750,000 to zero across the term.
Under Interest-Only (Followed by P&I)
On a 5-year IO period followed by P&I over the remaining 15 years, the IO monthly repayment is approximately $4,063 (interest only on $750,000 at 6.5%). After year 5, the loan reverts to P&I over 15 years on the unchanged $750,000 balance, producing monthly repayments of approximately $6,535. Total repayments across the 20-year term are approximately $1,420,000, of which $670,000 is interest.
The Headline Difference
The IO structure produces a monthly cash flow saving of approximately $1,531 during the 5-year IO period (around $91,860 across the IO years). However, total interest paid across the full 20 years is approximately $77,000 higher under IO than under P&I, and the post-IO repayment jumps to roughly $6,535, which is $941 per month higher than the original P&I repayment would have been. The structural trade-off is visible in both directions.
Comparison 1: Cash Flow
Cash flow is the dimension where P&I and IO differ most visibly. Both structures involve the same interest rate on the same loan balance, but how that translates into regular repayments diverges meaningfully.
P&I Cash Flow Profile
P&I produces a constant repayment for the full term of the loan (assuming the rate stays constant). On the worked example, this is $5,594 a month for 240 months. The borrower has predictability across the full term and faces no scheduled step-up in repayments. Cash flow planning is simpler under P&I because the repayment does not change structurally over the loan’s life.
IO Cash Flow Profile
IO produces two distinct phases: a lower repayment during the IO period ($4,063 in the worked example) followed by a higher P&I repayment after IO ends ($6,535 in the worked example). The cash flow profile is uneven: substantial savings during the IO period, followed by a step-up that the borrower needs to fund from improved income or a refinance.
The Practical Cash Flow Implications
IO suits borrowers prioritising cash flow during a defined period: investors building portfolios, businesses managing growth phases, or borrowers planning to refinance or exit before the IO ends. P&I suits borrowers prioritising predictability across the full term and steady commitment to clearing the loan. Both involve the same total cost over time; IO simply shifts the timing of the principal repayment.
Stress-Testing Both Cash Flow Profiles
Borrowers should stress-test both structures at higher rates before choosing. The P&I scenario stress-tests as a steady increase across the full term. The IO scenario stress-tests two ways: a rate increase during the IO period (increasing the IO repayment) and a rate environment at the end of the IO period that compounds the step-up. The post-IO repayment in the worked example at 8.5% (a 2% rate increase) would be approximately $7,381 a month, around $2,300 higher than the original IO repayment.
Comparison 2: Risk
Both structures expose borrowers to interest rate risk over the loan’s life, but the specific risks differ. Understanding which structure carries which risks helps borrowers choose with their eyes open.
P&I Risk Profile
P&I exposes the borrower to interest rate risk evenly across the loan term. Rate changes affect the variable rate component of the repayment, but the loan amortises predictably regardless. There is no scheduled step-up in repayments, no balloon balance falling due, and no refinancing event built into the structure (although refinancing can still happen at the borrower’s choice). The main risks are rate movement and any covenant tests imposed at annual reviews.
IO Risk Profile
IO carries the same rate risk as P&I during the loan’s life, plus three additional risks specific to the structure. First, the post-IO step-up risk: repayments increase materially when the IO period ends, by 30% to 60% depending on the rate environment. Second, the refinancing risk: many borrowers plan to refinance at IO maturity rather than absorb the step-up, but the refinancing pathway depends on lender appetite at that time. Third, the lender policy risk: IO renewals are not guaranteed, and prudential standards on IO lending have tightened over time.
Renewal and Refinancing Risk Specifically
Renewal risk is the most underestimated IO-specific risk. APRA’s prudential settings have restricted IO lending in residential mortgages, and similar tightening has flowed into some commercial lending policies. A borrower expecting to roll IO continuously through the loan’s life may find lender appetite has changed by the time the renewal is needed. P&I does not carry this risk because there is no renewal event built into the structure.
Equity Buffer as a Risk Mitigant
P&I builds equity steadily across the loan’s life, which gives the borrower a growing buffer against property value declines. Under the worked example, P&I builds approximately $86,000 of equity in the first 5 years (the principal repaid during that period). IO builds zero equity through principal repayment during the IO period; any equity build under IO comes purely from capital growth in the property. In a flat or declining market, this difference is significant.
Comparison 3: Tax Treatment
Tax treatment differs between P&I and IO in ways that matter for some borrowers but not others. The differences depend on whether the loan funds an investment property or owner-occupier business premises, and on the borrower’s broader tax position.
Interest Deductibility for Investment Property
For commercial property held as investment, interest paid on the loan is generally tax-deductible against the rental income. Under both P&I and IO, the interest portion of each repayment is deductible. The difference is how much of each repayment is interest. Under IO, every dollar of the IO repayment is interest, so 100% is deductible. Under P&I, the interest portion decreases over time as the principal reduces, so the proportion of each repayment that is deductible falls.
Tax Deductibility in the Worked Example
In year 1 of the worked example under P&I, the borrower pays approximately $48,000 in interest (deductible) and $19,000 in principal (not deductible). Under IO, the same year produces approximately $48,750 in interest, all of which is deductible. The deductibility position is similar in year 1 but diverges over time as the P&I balance reduces. By year 10 under P&I, the interest portion has fallen to approximately $33,000, with principal repayment having risen accordingly. Under IO during the same year (if still in IO), interest remains at approximately $48,750.
Owner-Occupier Tax Treatment
For owner-occupier commercial property, interest is generally deductible against the occupying business’s income. The same dynamics apply: IO maximises the deductible portion of each repayment, while P&I shifts more of each repayment into the non-deductible principal category over time. Owner-occupiers building equity in their premises long-term often accept this trade-off because the equity build delivers other benefits, while investors may prefer to maximise deductibility under IO.
Asset Depreciation and Other Tax Effects
Beyond interest deductibility, commercial property generates depreciation deductions on building costs and fixtures, which are independent of the loan structure. SMSF commercial property under a limited recourse borrowing arrangement (LRBA) has its own tax treatment that interacts with both P&I and IO differently. Tax considerations should always be discussed with an accountant familiar with the borrower’s broader position before the structural choice is finalised.
Comparison 4: Equity Building
The two structures differ fundamentally in how the borrower builds equity in the underlying asset. The difference matters more for some borrowing strategies than others.
How P&I Builds Equity
Under P&I, every repayment reduces the loan balance, which directly increases the borrower’s equity in the asset. The pace of equity build is slow at first (early repayments are mostly interest) and accelerates over time. Under the worked example, principal reduction in year 1 is approximately $19,000; by year 10 it is approximately $34,000 per year; by year 19 it is approximately $61,000. Total equity built through principal repayment over 20 years is the full $750,000 balance.
How IO Builds (or Does Not Build) Equity
Under IO, principal does not reduce during the IO period, so the borrower builds no equity through loan repayment. Any equity build during this period must come from capital appreciation in the underlying asset. After IO ends, the loan transitions to P&I (over the remaining shorter term), and equity build accelerates compared with a standard P&I loan because the principal is being repaid over fewer years.
Equity Build in Combination with Capital Growth
In rising markets, both structures build equity, but P&I builds equity through both loan reduction and capital appreciation, while IO builds equity through capital appreciation alone (during the IO period). In flat markets, P&I continues to build equity through loan reduction; IO does not. In declining markets, P&I provides a buffer through accumulated principal repayment; IO offers no such buffer until the IO period ends.
Strategic Implications
Borrowers building long-term wealth in a single owner-occupier property typically benefit from P&I’s steady equity build, particularly if capital growth is uncertain. Investors building portfolios and intending to leverage equity into additional properties often prefer IO because the cash flow saved can fund other deposits, with capital growth in the existing properties handling the equity build. Both strategies work; they suit different goals.
Comparison 5: Lender Approval
The final dimension is how lenders treat each structure during the assessment process. Approval criteria differ between P&I and IO in ways that affect both initial approval and ongoing access.
Lender Approval for P&I
P&I is the default structure most lenders prefer and approve most readily. The loan amortises predictably to zero, the lender’s exposure reduces over time, and there is no renewal event introducing structural risk. Lenders typically apply standard serviceability assessment against the P&I repayment, with the borrower needing to demonstrate cash flow comfortably covers the obligation.
Lender Approval for IO
IO faces tighter approval criteria. Lenders typically require stronger borrower profiles, lower LVRs, and assess serviceability against both the IO repayment and the eventual post-IO P&I repayment. Some lenders apply additional buffers when assessing IO applications, reflecting the structural risk that the borrower may not be able to afford the step-up when IO ends.
Serviceability Buffers and Structural Tests
Australian Prudential Regulation Authority (APRA) requires authorised deposit-taking institutions to apply a 3% buffer above the loan rate when assessing residential serviceability. Commercial lenders are not bound by the same formal requirement, but many apply similar internal buffers to commercial assessments, particularly for IO structures where the post-IO step-up is a known future risk. The buffer effectively requires the borrower to demonstrate they can service the loan at higher rates as well as the agreed rate.
Industry and Asset Class Differences
Lender approval criteria for both structures also vary by industry and asset class. Specialised property and certain industries face tighter terms under both P&I and IO, with IO often being unavailable on the most specialised assets. How lenders view different loan structures explores how lender assessment varies across specialist deals, with the framework applying to the P&I vs IO decision as well as broader pricing decisions.
Renewal and Restructure Approvals
Beyond initial approval, both structures involve ongoing lender engagement at annual reviews. P&I reviews are typically routine monitoring exercises. IO reviews can be more substantial, particularly as IO maturity approaches, because the lender is assessing whether to extend IO, transition to P&I, or restructure the deal. Borrowers approaching IO maturity benefit from engaging with the lender 6 to 12 months in advance rather than waiting for the deadline.
Side-by-Side Summary
Drawing the five dimensions together produces a clear comparison reference. Both structures have their place, and the right choice depends on which trade-offs fit the borrower’s situation.
Cash Flow
P&I: Higher constant repayment across full term, predictable, no step-up. IO: Lower repayment during IO period, materially higher repayment afterwards, predictable within each phase but with a clear shift between them.
Risk
P&I: Rate risk only, no structural step-up, no refinancing event built in. IO: Rate risk plus step-up risk plus refinancing risk plus lender policy risk on IO renewals.
Tax
P&I: Interest portion of each repayment is deductible, but the deductible proportion falls over time. IO: 100% of IO repayment is deductible during the IO period; deductibility reduces after transition to P&I.
Equity
P&I: Steady equity build through principal repayment from day one, accelerating over time. IO: No equity build through repayments during IO period; relies on capital growth in the asset.
Lender Approval
P&I: Default structure, broader lender support, standard serviceability assessment. IO: Tighter approval criteria, additional buffers often applied, narrower lender pool, renewal not guaranteed.
When Each Structure Typically Fits
Although the comparison above maps the trade-offs, a brief summary of when each structure typically fits helps borrowers position their own situation.
P&I Typically Suits
Owner-occupier commercial property buyers building long-term equity in their premises. Borrowers prioritising predictability across the loan’s life. Borrowers without a clear refinancing pathway at any defined future point. Borrowers operating in industries or asset classes where lender appetite for IO is tighter.
IO Typically Suits
Commercial property investors managing portfolio cash flow during the early years of ownership. Borrowers funding premises purchases during defined business growth phases where revenue is expected to rise. Borrowers using bridging or transitional finance with a clear short-term exit. SMSF commercial property purchases where tax structuring and the LRBA framework align with IO mechanics.
Where the Choice Is Less Obvious
Owner-occupier deals where the business cash flow is comfortable but cash reserves are wanted for other purposes can go either way. Investor deals where capital growth expectations are modest also blur the distinction, since the equity build advantage of P&I becomes relatively more important. Talking through the specific situation with a specialist broker usually clarifies which structure delivers better outcomes given the borrower’s actual goals.
Practical Pointers for Choosing Between Them
A few practical habits help borrowers make the P&I vs IO choice deliberately rather than by default.
Model Both Structures Side by Side
Before agreeing to either structure, run the comparison: regular repayments under each, total cost across the loan’s life, the post-IO step-up if applicable, and the equity build profile over the planned holding period. The decision is easier when both options are visible together.
Stress-Test Both Structures at Higher Rates
Run both scenarios at 2% to 3% above the current rate. P&I stress-tests as a higher repayment across the full term; IO stress-tests as both a higher IO repayment and a meaningfully larger post-IO step-up. Whichever structure still fits comfortably under stress has more resilience.
Discuss Tax Treatment with an Accountant
The interest deductibility differences are real but specific to the borrower’s tax position. An accountant familiar with the wider picture (income, deductions, depreciation, entity structure) can model the after-tax cost of each structure, which often differs from the headline pre-tax cost comparison.
Check Lender Policy Before Committing to IO
If IO is being considered, confirm the specific lender’s policy on IO availability, IO period length, and IO renewals. Lender appetite shifts over time, and the IO option that was available a year ago may have tightened. Knowing what the lender will actually approve avoids structuring expectations around assumptions that turn out not to hold.
Plan the Exit If Choosing IO
If IO is the chosen structure, define the exit at the start: how the post-IO repayment will be funded, what refinancing options will be sought, what happens if refinancing is not available on similar terms. The choice between P&I and IO is meaningfully different when each is treated as a fully planned structure rather than a default.
Where to Read About Lender Serviceability Approaches
Lender approval criteria for both P&I and IO loans are shaped by the prudential framework that governs Australian banks. While the specific rules apply most directly to residential lending, the underlying principles around stress-testing repayments and applying buffers translate into commercial lender policy across both structures.
The Australian Prudential Regulation Authority’s overview of macroprudential policy settings and the serviceability buffer at apra.gov.au explains how the regulator sets serviceability buffer expectations for authorised deposit-taking institutions and what role the buffer plays in protecting borrowers against rate movements and unforeseen changes in income or expenses. The framework directly influences how commercial lenders structure their own assessment of P&I and IO loan applications.
Frequently Asked Questions (FAQs)
1. Which is cheaper overall, P&I or IO?
P&I is usually cheaper over the loan’s full life because the principal balance reduces from day one, meaning interest accrues on a smaller balance each month. IO keeps the balance constant during the IO period, so interest continues accruing on the full original balance for longer. In the worked example, IO produces approximately $77,000 more total interest over the 20-year term than P&I. The headline savings during the IO period come at the cost of higher total interest.
2. Can I switch from IO to P&I mid-loan?
Usually yes, often at no cost. Most commercial lenders allow borrowers to switch from IO to P&I before the IO period ends if cash flow allows the higher repayment. The switch typically requires a formal request to the lender and may involve updated paperwork, but it is generally straightforward. The reverse switch (P&I to IO) is less common and usually requires a full reassessment under the lender’s current IO policy.
3. Does P&I get cheaper interest rates than IO?
Generally yes, by 0.10% to 0.30%. Lenders typically price IO slightly higher than comparable P&I because the lender’s exposure stays constant during the IO period rather than reducing through principal repayment. The pricing premium is modest on a per-payment basis but adds up over the loan’s life. Combined with the higher total interest from the structure itself, this is part of why IO costs more overall than P&I.
4. Is IO better for tax than P&I?
It depends on the borrower’s situation. For investment property where interest is tax-deductible, IO maximises the deductible portion of each repayment (since 100% of the IO repayment is interest). Under P&I, the deductible proportion falls over time as principal repayment grows. However, P&I builds equity that is not tax-deductible but creates wealth, while IO builds no equity through repayment. The after-tax comparison depends on the borrower’s marginal tax rate, broader investment strategy, and planning horizon.
5. Why do lenders restrict IO more than P&I?
IO carries structural risks that P&I does not. The borrower’s loan balance does not reduce during the IO period, the post-IO repayment step-up creates an affordability test the lender wants to be confident about, and refinancing at IO maturity depends on conditions at that time. Regulators have also tightened standards on IO lending periodically, which feeds through into commercial lender policy. The combined effect is tighter approval criteria for IO than for comparable P&I deals.
6. Can a commercial property loan combine P&I and IO?
Yes, in two common ways. First, a loan can have an IO period followed by a P&I revert, which is the standard IO structure. Second, a borrower can split a single loan into two facilities, one P&I and one IO, structured to balance cash flow against equity build. The split structure suits borrowers wanting some predictability and some flexibility. Specialist commercial brokers can usually structure these splits across most lenders.
7. What happens to my equity if I choose IO and the property value falls?
Under IO, the borrower has no buffer from principal repayment during the IO period. If the property’s value falls, the LVR rises, and any subsequent refinancing event (including IO renewal or transition to P&I) may face tighter LVR limits than the original loan. P&I provides a steady buffer of accumulated principal repayment that protects against value declines. This is one of the more underappreciated risks of IO in markets where capital growth is uncertain.
The Bottom Line
Principal and interest and interest-only commercial loans produce materially different outcomes across cash flow, risk, tax, equity-building, and lender approval. P&I produces higher constant repayments, lower total interest, steady equity build, and broader lender support. IO produces lower repayments during the IO period, higher total interest over the loan’s life, deferred equity build, and tighter lender restrictions. Neither structure is universally better; each suits different borrower situations and goals.
For most borrowers, the smartest approach is to model both structures side by side against the actual deal, stress-test each at higher rates, and choose deliberately based on which trade-offs match the borrower’s cash flow priorities, equity-building goals, and intended holding period. A specialist commercial broker can usually run the comparison efficiently and identify which structure the available lenders will actually approve. The choice between P&I and IO is one of the higher-impact structural decisions in commercial lending; making it with the comparison clearly in front of the borrower produces better outcomes than defaulting in either direction.
