Bridging Loan Peak Debt Interest Calculation: How Lenders Work Out What You Actually Pay

A bridging loan peak debt interest calculation determines the interest charged during the overlap period when you simultaneously hold debt on both your existing property and the new one you’re purchasing. According to APRA’s latest quarterly property exposure statistics for Q1 2026, bridging finance accounts for approximately 2.3% of the total $2.1 trillion Australian residential mortgage book, representing roughly $48 billion in outstanding bridging debt. I’ve walked through this calculation with hundreds of clients over the past decade, and the mechanics are surprisingly consistent across lenders—once you understand the three components driving the number.

What Exactly Is Peak Debt in a Bridging Loan?

Peak debt is the maximum combined loan balance you carry during the bridging period. It’s not a separate loan product—it’s a calculation point that determines your interest cost. When I structure a bridging facility for a client, the peak debt figure typically includes three elements.

First, you have the outstanding balance on your existing property’s mortgage. Second, you add the full purchase price of the new property plus stamp duty and acquisition costs. Third, you subtract any cash deposit you’re contributing from savings. The resulting figure is the gross peak debt—the total amount the lender is funding before you sell your existing home.

For example, if you owe $380,000 on your current mortgage and you’re buying a $920,000 property with $48,000 in stamp duty, your total outlay is $1,348,000. If you have $120,000 in cash savings going toward the purchase, your peak debt sits at $1,228,000. That’s the balance on which interest accrues until settlement of your existing property sale.

Most lenders express this as a single loan facility with a limit equal to the peak debt. You draw down what you need at settlement of the new purchase, and the limit reduces as you pay down the old loan from sale proceeds. The key point I emphasise to clients is that you only pay interest on the drawn balance, not the limit—but during the overlap, the drawn balance equals the peak debt.

How Lenders Determine the Peak Debt Figure

The calculation methodology is remarkably standardised across the major banks. CBA, Westpac, NAB, and ANZ all use a variation of the same formula, though the specific treatment of costs and credits differs slightly. Based on my analysis of current product disclosure statements as of May 2026, here’s the standard framework.

The lender starts with the new property purchase price. They add estimated stamp duty, which varies by state—in NSW, that’s $40,457 for an $920,000 owner-occupied purchase under current FY25-26 rates. They add legal costs, typically $2,000 to $3,500 for a standard conveyance. They add any loan establishment fees, which range from $0 to $600 depending on the lender and product. Then they subtract your available cash contribution.

The existing loan balance gets added to this figure, creating the total peak debt. Some lenders also capitalise the first month’s interest and any LMI premium into the peak debt calculation, which pushes the number higher. I’ve seen cases where capitalised costs add $15,000 to $25,000 to the peak debt figure, which directly increases the interest you’ll pay during the bridge.

The Interest Calculation Mechanics: Three Variables That Drive Your Cost

The bridging loan peak debt interest calculation comes down to three variables: the peak debt balance, the interest rate, and the duration of the bridging period. Multiply these together, adjust for daily accrual, and you have your interest cost. The formula is straightforward, but the assumptions behind each variable are where clients often misunderstand the true cost.

Interest on a bridging loan accrues daily on the outstanding balance. Most Australian lenders calculate this as (peak debt × annual interest rate ÷ 365) × number of days in the bridging period. Some use 366 days in leap years, but the difference is immaterial for a typical 90 to 180-day bridge.

The interest rate applied is typically the lender’s standard variable rate plus a margin. As of May 2026, with the RBA cash rate at 4.10%, major bank standard variable rates for owner-occupiers sit around 6.60% to 6.90% p.a. Bridging loans often carry an additional 0.50% to 1.00% margin, pushing the effective rate to 7.10% to 7.90% p.a. I’ve seen some second-tier lenders offer bridging rates as low as 6.85% p.a., but these typically come with stricter servicing requirements.

Worked Example: A 120-Day Bridge

Let’s run the numbers on a realistic scenario. Assume peak debt of $1,224,000 at an interest rate of 7.50% p.a. over a 120-day bridging period.

Daily interest = $1,224,000 × 7.50% ÷ 365 = $251.51 per day.

Total interest for 120 days = $251.51 × 120 = $30,181.

That’s the interest cost you’ll pay for the bridging period. It’s not a separate fee—it’s simply the interest that accrues on your loan balance during the overlap. If your existing property sells in 60 days instead of 120, the interest drops to approximately $15,090. The duration variable is the one you have the most control over, which is why I always recommend aggressive pricing and marketing of the existing property before committing to a bridge.

Capitalised vs. Monthly Repayments

Most bridging loans in Australia are structured with capitalised interest—meaning the interest accrues and gets added to the loan balance rather than requiring monthly repayments during the bridge. This is both a convenience feature and a cost amplifier.

When interest is capitalised, you’re effectively paying interest on the interest. Using the 120-day example above, if the $30,181 in interest is capitalised monthly, the second month’s interest calculation includes the first month’s accrued interest in the balance. This compounding effect adds approximately $300 to $500 to the total cost over a four-month bridge. It’s not a deal-breaker, but it’s a detail worth understanding.

Some lenders offer a monthly repayment option where you service the interest as it accrues. This avoids the compounding effect but requires cash flow during a period when you’re already stretched. For most owner-occupiers, the capitalised structure is the default and the pragmatic choice—just factor the compounding into your cost estimate.

End Debt Calculation: What Happens After the Bridge

The end debt is what remains after you sell your existing property and apply the sale proceeds to the bridging loan. This is the permanent loan you’ll carry forward, and it’s the figure lenders use for servicing assessment under APRA’s current 3.0% serviceability buffer.

The end debt calculation follows a simple logic: peak debt minus net sale proceeds from your existing property. Net sale proceeds means the sale price minus agent commission, marketing costs, legal fees for the sale, and the discharge of the existing mortgage.

If your existing property sells for $750,000, with agent commission of 2.2% ($16,500), marketing costs of $4,000, and legal fees of $1,500, your gross proceeds are $728,000. After discharging the $380,000 mortgage, net proceeds are $348,000.

End debt = $1,224,000 (peak debt) - $348,000 (net proceeds) + $30,181 (capitalised interest) = $906,181.

This $906,181 becomes your ongoing home loan. The lender assessed your ability to service this end debt when you applied for the bridging loan—not the peak debt. This is a critical distinction. APRA’s servicing guidelines require lenders to assess the end debt at the actual interest rate plus a 3.0% buffer, which as of May 2026 means assessing at approximately 9.50% to 10.00% p.a. for most borrowers.

LVR Considerations on End Debt

The loan-to-value ratio on the end debt determines whether you’ll pay Lenders Mortgage Insurance. Using the example above, the end debt of $906,181 against a new property valued at $920,000 gives an LVR of 98.5%—well into LMI territory.

However, most lenders assess the LVR on the combined security position during the bridging period. If your existing property is worth $750,000 and the new property is worth $920,000, the total security value is $1,670,000 against a peak debt of $1,224,000—an LVR of 73.3%. This is below the 80% LMI threshold, which means LMI may not apply even though the end debt LVR is high.

This is one of the structural advantages of bridging finance. The lender takes a combined view of the securities during the bridge, which often results in a more favourable LMI outcome than if you sold first and then bought with a smaller deposit. I’ve structured bridges where clients avoided $15,000 to $25,000 in LMI premiums purely because the combined security LVR stayed under 80%.

Lender-Specific Approaches: How the Major Banks Calculate Peak Debt Interest

While the formula is standardised, the application of it varies enough between lenders that the difference in total interest cost can be $2,000 to $5,000 on a typical bridge. Here’s what I’m seeing across the major banks as of May 2026.

CBA Bridging Loan Structure

Commonwealth Bank offers bridging finance under their standard variable rate home loan product with a bridging period of up to 12 months. Their peak debt calculation includes the full purchase price, stamp duty, and legal costs, but they exclude LMI from the peak debt if it’s payable—instead adding it to the end debt. This slightly reduces the interest cost during the bridge compared to lenders who capitalise LMI into the peak debt.

CBA’s current standard variable rate for owner-occupiers with principal and interest repayments is 6.64% p.a. (comparison rate 6.67% p.a. as of May 2026). Their bridging margin is typically 0.50%, taking the effective bridging rate to 7.14% p.a. Interest is calculated daily and capitalised monthly.

Westpac Bridging Loan Structure

Westpac structures their bridging facility with a 6-month standard term, extendable to 12 months by application. Their peak debt calculation is more conservative—they include a buffer for cost overruns and typically add 5% to the estimated stamp duty and legal costs. This results in a slightly higher peak debt figure than CBA for the same transaction.

Westpac’s standard variable rate sits at 6.79% p.a. for owner-occupiers as of May 2026, with a bridging margin of 0.75%, taking the effective rate to 7.54% p.a. They offer both capitalised and monthly repayment options.

NAB and ANZ Approaches

NAB’s bridging product uses their base variable rate of 6.69% p.a. with a 0.60% bridging margin (7.29% p.a. effective). They’re notable for offering a 12-month bridging period as standard, which provides more flexibility if the sale of your existing property takes longer than expected.

ANZ applies their standard variable rate of 6.72% p.a. with a 0.70% margin (7.42% p.a. effective) and offers bridging terms of up to 12 months. ANZ’s peak debt calculation is the most transparent of the major banks—they provide a detailed breakdown in their loan offer document that itemises every component of the peak debt figure.

The Real Cost Drivers: What Actually Moves the Needle

After structuring bridging finance for over a decade, I’ve identified five factors that genuinely move the total interest cost. These are what I focus on when advising clients, because they’re the levers you can pull.

1. The Speed of Your Existing Property Sale

This is the single biggest cost driver. Every additional week your existing property sits on the market adds approximately $1,760 in interest on a $1.22 million peak debt at 7.50% p.a. Over a month, that’s $7,545. The difference between selling in 4 weeks versus 12 weeks is roughly $15,000 in additional interest.

I recommend clients have their existing property listed and under contract before committing to a bridge, or at minimum have it on the market with a realistic price expectation. The bridging loan works best when the existing property is already in the sales pipeline, not when you’re starting the sales process from scratch after purchasing the new home.

2. The Interest Rate Margin

The 0.50% to 1.00% margin above standard variable rates might not sound significant, but on a $1.22 million peak debt over 120 days, a 0.50% difference in the margin equals approximately $2,000 in additional interest. Across the major banks, the margin spread is 0.50% to 0.75%, which translates to a $1,000 to $1,500 difference in total interest cost for a typical bridge.

3. Capitalised Costs

Every dollar of cost that gets capitalised into the peak debt accrues interest for the duration of the bridge. If you can pay stamp duty and legal costs from cash reserves rather than capitalising them, you reduce the peak debt and the associated interest. On a $48,000 stamp duty bill, paying it from cash rather than capitalising it saves approximately $1,180 in interest over a 120-day bridge at 7.50% p.a.

4. The End Debt Servicing Assessment

While not a direct interest cost, the end debt servicing assessment determines whether you qualify for the bridging loan at all. Under APRA’s 3.0% buffer, lenders assess your ability to service the end debt at the product rate plus 3.0%. For a $906,000 end debt, that means assessing at roughly 10.50% p.a., which requires a gross annual income of approximately $150,000 to $170,000 for a single borrower depending on the lender’s specific servicing calculator.

5. Contingency for Extended Bridge Periods

If your existing property doesn’t sell within the bridging term, the lender may require you to switch to a standard variable rate loan on the full peak debt—without the bridging structure. This is a worst-case scenario that I’ve seen happen perhaps 5% of the time, usually when the property market softens unexpectedly. Having a contingency plan—whether it’s rental income from the existing property or a backup sale price floor—is essential.

Common Mistakes in Peak Debt Interest Calculations

Over the years, I’ve seen clients and even some brokers make consistent errors when estimating bridging loan costs. Here are the five most common mistakes and how to avoid them.

Mistake 1: Forgetting to include stamp duty in the peak debt. Stamp duty is a material cost. In NSW, stamp duty on a $920,000 owner-occupied purchase is $40,457 as of FY25-26. Omitting this from the peak debt calculation understates the interest cost by approximately $1,000 over a 120-day bridge.

Mistake 2: Assuming the bridging rate equals the standard variable rate. The margin matters. At 7.50% p.a. effective versus 6.70% p.a. SVR, the difference on a $1.22 million peak debt over 120 days is roughly $3,200. Always use the effective bridging rate, not the advertised SVR.

Mistake 3: Ignoring the compounding effect of capitalised interest. If interest is capitalised monthly, the second month’s interest calculation includes the first month’s accrued interest. This adds approximately 0.5% to 1.0% to the total interest cost over a four-month bridge. It’s not huge, but it’s real.

Mistake 4: Overestimating net sale proceeds. Agent commission, marketing, and legal fees for the sale typically consume 2.5% to 3.5% of the sale price. On a $750,000 sale, that’s $18,750 to $26,250. If you overestimate net proceeds, you underestimate end debt, which affects both your cost estimate and your servicing assessment.

Mistake 5: Not stress-testing the end debt servicing. Even if you qualify for the bridging loan today, changes in your income, expenses, or the lender’s servicing calculator can affect approval. I always recommend running the servicing numbers with a 10% buffer on the end debt to account for rate movements and cost overruns.

How to Minimise Your Bridging Loan Interest Cost

Based on the deals I’ve structured, here are the practical steps that reduce the peak debt interest calculation outcome.

Get your existing property under contract before you bid on the new one. This is the single most effective strategy. If your existing property is sold subject to a settlement date that aligns with your new purchase, you may not need a bridging loan at all. If you do need one, the bridging period is minimised.

Negotiate the bridging margin. Some lenders will reduce or waive the bridging margin if you have a strong overall application—high income, low LVR on the end debt, and a property in a high-demand suburb. A 0.25% margin reduction on a $1.22 million peak debt over 120 days saves approximately $1,000.

Pay costs from cash where possible. Every dollar of stamp duty, legal fees, and establishment costs you pay from cash reduces the peak debt and the associated interest. If you have the savings, use them.

Choose a lender with a longer standard bridging term. A 12-month term gives you breathing room if the sale takes longer than expected. The interest cost is higher if you use the full term, but the alternative—having the lender demand repayment or switch you to a higher rate—can be far more expensive.

Run the numbers on both capitalised and monthly repayment options. If you have the cash flow to make monthly interest payments during the bridge, you avoid the compounding effect and reduce the total interest cost by approximately $300 to $500 on a typical bridge. It’s not a huge saving, but it’s worth considering if cash flow allows.

Frequently Asked Questions

Q: Is the interest on a bridging loan tax-deductible?

A: It depends on the purpose of the new property. If the new property is your primary residence, the bridging loan interest is generally not tax-deductible. If the new property is an investment property, the interest on the portion of the loan attributable to the investment property may be deductible. However, the ATO’s treatment of bridging loan interest is complex, and I strongly recommend getting specific advice from a registered tax agent. The deductibility hinges on the purpose of the borrowings at the time the interest is incurred, and the mixed-use nature of bridging finance makes this a grey area.

Q: What happens if my existing property doesn’t sell within the bridging period?

A: Most lenders will assess the situation at the end of the bridging term. If the property is on the market and receiving interest, they’ll typically extend the bridging period by 3 to 6 months. If the property isn’t selling, they may require you to switch to a standard variable rate loan on the full peak debt, which increases your monthly repayments significantly. In the worst case, they may require you to rent out the existing property and use the rental income to service the debt. This is why I always recommend having a realistic sale price and a backup plan before committing to a bridge.

Q: Can I make extra repayments during the bridging period to reduce interest?

A: Yes, most bridging loans allow extra repayments without penalty, especially if the loan is on a variable rate. Any extra repayment reduces the outstanding balance and the daily interest accrual. If you have surplus cash flow during the bridge, making extra repayments is an effective way to reduce the total interest cost. However, check the specific product terms—some fixed-rate bridging products may have restrictions on extra repayments.

Q: How does the peak debt interest calculation differ for investment properties?

A: The calculation mechanics are identical, but the interest rate is typically higher. Investment property bridging loans carry an additional margin of 0.20% to 0.50% above owner-occupied rates. As of May 2026, investment bridging rates range from 7.30% to 8.30% p.a. depending on the lender. The peak debt calculation also includes any capitalised LMI, which is more common on investment loans due to typically higher LVRs.

Q: Is a bridging loan more expensive than selling first and renting?

A: It depends on the numbers. A 120-day bridge on $1.22 million at 7.50% p.a. costs approximately $30,000 in interest. Selling first and renting for 4 months might cost $12,000 to $16,000 in rent, plus $3,000 to $5,000 in moving costs, storage, and double-handling. The bridging loan is more expensive in pure dollar terms, but it avoids the disruption of moving twice and the risk of being priced out of the market while you’re renting. The decision is as much about lifestyle and market timing as it is about cost.

Q: Do all lenders offer bridging loans?

A: Most major banks and many second-tier lenders offer bridging finance, but not all. The major four (CBA, Westpac, NAB, ANZ) all have bridging products. Among second-tier lenders, Bankwest, Suncorp, and ING offer bridging loans, while some online lenders like Athena and loans.com.au do not. Non-bank lenders like Pepper Money and La Trobe Financial offer bridging finance but typically at higher rates and with stricter terms. Availability also depends on the specific transaction structure—some lenders only offer bridging loans for purchases where the existing property is already on the market.

If you’re weighing up whether a bridging loan makes sense for your situation, the peak debt interest calculation is the starting point—but it’s only one piece of the puzzle. The full picture includes your sale timeline, your servicing capacity, and your appetite for the financial overlap. Feel free to reach out to my team if you’d like a tailored calculation based on your specific numbers.

Data note: Interest rates and product features in this article are as of May 2026, sourced from each lender’s official product disclosure statements and rate sheets. Stamp duty calculations reflect FY25-26 NSW Revenue rates for owner-occupied purchases. Property market data is based on CoreLogic Q1 2026 reporting and APRA quarterly ADI property exposure statistics. Rates and policies change frequently; consult a licensed professional before making decisions.

Disclaimer: This article is general information only and does not constitute personal financial, tax, legal, or credit advice. Interest rates and loan product terms are sourced from each lender’s official product pages as of May 2026. Tax treatment of bridging loan interest depends on individual circumstances—consult a registered tax agent. Arrivau Pty Ltd (ABN 81 643 901 599) provides credit assistance as an ASIC Credit Representative (CRN 530978) under its licensee’s Australian Credit Licence. Speak to a licensed professional before acting on any information in this article.