How much can I borrow on a second mortgage? The arithmetic, step by step

Most owners who ask this are holding a rough number: “the place is worth about this, I owe about that.” The real answer is a short piece of arithmetic, and it is more sensitive to two inputs than people expect: the valuation and the first loan’s limit. Here is the calculation in order.

What is the formula for a second mortgage amount?

Second mortgage = valuation × combined LVR − first mortgage limit

Combined LVR counts every loan secured on the property against its value. A second lender ranks behind the first, so it only gets paid after the bank is cleared. That is why it works from a ceiling on total debt and then subtracts what is already there.

Use these as planning bands, not lender policy:

Combined LVR	Comfortable	Workable	Stretch
Residential	up to 65%	65% to 75%	75% to 80%
Commercial	up to 55%	55% to 65%	65% to 70%

The combined LVR page explains the buffer logic behind them. For the idea of paper versus lendable equity, see usable equity vs paper equity.

How do you work it out, step by step?

1. Get a realistic value. Use recent sales of similar properties, or an agent’s appraisal, then treat it as a guess. The lender’s valuer will set the real figure.
2. Pick a band. Choose the comfortable band to plan, then see what the workable band adds.
3. Multiply. Value × band = maximum total secured debt.
4. Subtract the first mortgage limit. Not today’s balance. If there is redraw or a line of credit, use the limit.
5. Subtract costs you’ll fund from the loan. Fees and set-aside interest sit inside the gross amount. What is left is your usable cash.

Step 4 is the one people skip, so it gets its own section below.

Worked example 1: a house (illustrative)

A home is worth $1,200,000. The first mortgage has a balance of $500,000 but a limit of $560,000 because of redraw.

Combined LVR	Maximum total debt	Less $560,000 limit	Second mortgage
65%	$780,000	$560,000	$220,000
75%	$900,000	$560,000	$340,000
80%	$960,000	$560,000	$400,000

The comfortable answer is $220,000, and the stretch answer is $400,000. If you had used the $500,000 balance instead of the $560,000 limit, you would have expected $280,000 at the comfortable band, which is $60,000 more than a lender will count. Check your loan statement for the limit and the redraw available.

Worked example 2: commercial property (illustrative)

A warehouse is valued at $1,800,000 with a bank first mortgage of $700,000.

Combined LVR	Maximum total debt	Less $700,000	Second mortgage
55%	$990,000	$700,000	$290,000
65%	$1,170,000	$700,000	$470,000
70%	$1,260,000	$700,000	$560,000

The commercial bands run about ten points lower at each step, because commercial property is slower to sell and its value moves more. Commercial second mortgages covers how income and vacancy change the valuation.

What happens if the valuation comes in 10% lower?

This is the step most calculators leave out. The first mortgage doesn’t shrink when the value does, so the whole fall comes out of the second mortgage.

	House at $1,200,000	House at $1,080,000 (−10%)
65% band	$220,000	$142,000
75% band	$340,000	$250,000
80% band	$400,000	$304,000

At the comfortable band, a 10% valuation fall cuts the loan by about 35%. The commercial warehouse falls from $290,000 to $191,000 at 55% if it is valued 10% lower at $1,620,000, a drop of about a third.

That leverage works in your favour when values rise, and against you when they dip. The Reserve Bank’s October 2026 Financial Stability Review notes that housing prices “have fallen recently”, though it adds that most borrowers would still hold “positive equity buffers” even in a further 20 per cent fall. Both statements are true at once: a household can be comfortably in positive equity and still have a lower lendable figure than last year. So run your own plan at 10% below your estimate, and see how it feels. Our valuations page covers desktop estimates versus full inspections.

Which valuation will the lender use?

It depends on the amount, the combined LVR and the property. A desktop valuation reviews recent sales and automated data without a visit, so it is quick. A full valuation sends a valuer to inspect the property, which takes longer but can lift or lower the figure. The higher the combined LVR you ask for, the more likely a lender is to want the full inspection. If your plan only works at the stretch band, ask early which type will be ordered and who pays for it.

Is the ceiling the same as the right amount?

No. The ceiling is the most the security can support. The right amount is the smallest sum that does the job, and it should line up with a way out. Ask three questions:

• What is the money for? A defined purpose, such as stock for a confirmed order or a supplier deadline, is easier to size than a vague buffer.
• How does it get repaid? A sale, a refinance, a contract payment or trading cash flow are the usual routes. See exit plans.
• What does a lower amount do to the buffer? Borrowing less than the maximum keeps the combined LVR in the comfortable band, which tends to make the approval smoother and the refinance later easier.

If you want your own numbers rather than these round ones, the equity and LVR calculator runs the formula for each band, and see if you qualify once you have a figure in mind. A specialist can then test it against the actual title.

What else can cap the amount below the formula?

The formula gives a ceiling for the security. Several other things can pull the real answer lower:

• First mortgagee consent. The bank’s loan terms often restrict further security, and some banks consent only up to a stated total. See first mortgagee consent.
• Ownership. Co-owners, trusts and companies mean extra signatories, and an SMSF-owned property generally can’t be offered for a business loan. Co-owned property as security explains who signs.
• Title problems. An old undischarged mortgage, a caveat or an unpaid rates notice can reduce or delay what’s offered. A title search shows these in advance.
• Fees. Government registration charges and legal costs add up. What every state charges lists the registry figures.
• Purpose. This is business lending only. Describing the purpose accurately is part of getting an offer that settles.

How do you lift the number before you apply?

• Pay down the first loan or cancel unused redraw, which lowers the deducted limit dollar for dollar.
• Fix visible condition issues before the valuer arrives, and have recent comparable sales and improvement receipts ready.
• Clear title issues in advance so they don’t surface late.
• Combine two titles, where ownership allows, so the usable equity adds up. See two properties.
• Plan the exit first, so the lender sees a repayment route and not just a loan.

These moves are slow and cheap. They also pay off if you borrow later, since the arithmetic is the same each time. Planning around property equity is part of running a business with a reserve, as the business.gov.au guidance on cash flow suggests.

Ready to see what your equity supports?

You now have the formula. The next step is a person checking it against your actual title, valuation and first loan. The enquiry takes about 60 seconds, and there’s no credit check when you first enquire, so asking won’t touch your credit file. Your details don’t go out to a pile of lenders. They go to one specialist, and a real person works through your figures and calls you. Please fill the form in accurately, with the property value, what’s owed, the amount you want and who owns the property, so the first structure we discuss is the one that can settle. Property-secured funds from $20k to $250k are possible the same day, and up to $5m within 24 to 48 hours.

See what my equity supports →