Investment property calculator: the five numbers to run before you buy
There are five numbers to run before you buy an investment property, in this order: what you can borrow, the monthly repayment, the stamp duty, lenders mortgage insurance if your deposit is under 20%, and land tax. On a $750,000 home in New South Wales with a 10% deposit, you need about $118,900 in cash and face repayments near $4,227 a month.
People search for one calculator that tells them whether to buy. It does not exist, because the question has five parts and each one can stop the purchase on its own.
We will run all five on one example so you can see how they fit: a $750,000 established home in New South Wales, bought as an investment, with a 10% deposit.
The example, as at 18 August 2026
- Price: $750,000. Deposit: $75,000. Loan: $675,000
- Loan rate: 6.41%, the average for new investor loans in July 2026
- Bank test rate on that figure: 9.41%
- Stamp duty in New South Wales: $27,937
- Lenders mortgage insurance at 90%: about $15,977
Sources: Reserve Bank of Australia, Presm calculators
1. What can you borrow?
Start here, because it rules properties in or out before you fall for one.
The bank will not test you at 6.41%. It adds a 3 point buffer and tests you at 9.41%. On a $675,000 loan, that means showing you could pay about $5,631 a month, after your living costs and other debts.
There is a second check. Banks are limited in how many loans they can write where total debt is six times income or more. If this were your only debt, $675,000 is six times an income of $112,500. If you already have a home loan, add it in.
Run it: Borrowing Power.
2. What is the repayment?
This is what you really pay each month.
| Loan of $675,000, 30 years | Monthly repayment |
|---|---|
| At 6.41% | $4,227 |
| At the bank's 9.41% test rate | $5,631 |
Many investors choose interest only, which lowers the payment and leaves the debt untouched. At 6.41% the interest on $675,000 is about $3,606 a month.
Run it: Loan Repayment Calculator.
3. What is the stamp duty?
Duty is paid in cash, usually at or before settlement, and it varies a great deal by state.
On $750,000, an investor pays $27,937 in New South Wales, $26,775 in Queensland and $40,070 in Victoria.
Run it: Stamp Duty Calculator.
4. Will you pay lenders mortgage insurance?
If your deposit is under 20%, the lender takes out insurance that protects the lender, and you pay the premium.
| Premium | |
|---|---|
| 10% deposit | $15,977 |
| 15% deposit | $8,498 |
| 20% deposit | $0 |
Source: Presm LMI Calculator, New South Wales, August 2026. An estimate: each lender sets its own premium.
Going from a 10% deposit to 15% nearly halves the premium. At 20% it disappears.
The premium can usually be added to the loan, so it need not come from savings. You then pay interest on it for years.
Run it: LMI Calculator.
5. What land tax will you pay each year?
The first four numbers decide whether you can buy. This one is a cost of holding, and it arrives every year.
Land tax is charged on the value of the land, not the building. Each state sets its own threshold and rates, and your own home is normally exempt. Two properties at the same price in different states can have very different bills, and owning through a trust or company changes the answer again.
Run it: Land Tax Calculator. For trusts and companies, use the Entity Land Tax Simulator.
Putting it together
| Cash needed up front | 10% deposit | 20% deposit |
|---|---|---|
| Deposit | $75,000 | $150,000 |
| Stamp duty | $27,937 | $27,937 |
| Lenders mortgage insurance | $15,977 | nil |
| Total | $118,914 | $177,937 |
That leaves out legal fees, inspections and lender fees, which vary too much to put one figure on.
What we would add
The five numbers tell you whether you can buy. They do not tell you whether you should.
For that, look at what the property costs you each week after rent. Since the tax rules changed in June, check which side of them your purchase falls on: negative gearing is now law.
Frequently asked questions
What should an investment property calculator include?
Five things: how much you can borrow, the monthly repayment, the stamp duty, lenders mortgage insurance if your deposit is under 20%, and land tax. The first four decide whether you can buy. The fifth is a cost of holding.
How much deposit do I need for a $750,000 investment property?
With a 10% deposit in New South Wales you need about $118,900 up front: $75,000 deposit, $27,937 stamp duty and about $15,977 of lenders mortgage insurance, though the insurance can usually be added to the loan. With 20% you need about $177,900 and pay no insurance.
What is the repayment on a $675,000 investment loan?
About $4,227 a month at 6.41% on a 30 year principal and interest loan. That was the average rate for new investor loans in July 2026.
Do I pay land tax on an investment property?
It depends on the state and the value of the land. Each state has its own threshold, and your main home is normally exempt. Check your state with the land tax calculator before you buy, because the gap between states is large.
Sources
- Reserve Bank of Australia, lenders' interest rates, July 2026
- APRA, limit on high debt to income home loans
- Stamp duty and insurance figures are from the Presm Stamp Duty Calculator and LMI Calculator, August 2026
Repayments are our own arithmetic. This is general information, not financial or credit advice.