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Property investment calculators
New Zealand's most comprehensive suite of investment property calculators
Property investment calculator
Figure out whether a property is worth investing in or not
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Figure out whether a property is worth investing in or not
Successful investors know buying an investment property isn’t just about finding a nice house ... it’s about understanding the numbers.
Our Property Investment Calculator, shown above, helps you calculate the potential returns on an investment property.
But remember: the numbers you see are projections, not guarantees.
Property values, rents, interest rates, vacancy and expenses don’t move in a straight line. The actual numbers you experience will vary from year to year.
The calculator is designed to help you understand the potential long-term picture as well as compare different investment opportunities.
This article was last updated in August, 2026. We will continue to update the assumptions in this calculator as interest rates change.
There are 4 inputs for this calculator:
Let’s look at what each of these inputs means.
Purchase price – This is the price you expect to pay for the property.
The calculator uses this figure when working out the size of the investment. Together with your deposit and other inputs, it works out how much you need to borrow.
Property type – Here you can select whether the property is a New Build or an existing property.
Different types of property can have different costs and investment characteristics.
For instance, New Build properties generally need a 20% deposit; existing properties typically need a 30% deposit.
Deposit – This is the amount of cash you plan to contribute towards the purchase.
The larger your deposit, the less you generally need to borrow.
Purchase costs – These are the additional costs associated with buying the property, such as legal fees and other expenses.
These costs are important because they form part of the cash you need to put into the investment.
Is the deposit borrowed? This tells the calculator whether the deposit is coming from your own cash or whether you are borrowing it.
For example, if you use the No Cash Needed method, you’ll use equity in another property for the deposit.
This matters because borrowing money means more interest costs, which means cashflow will be lower.
Rent – This is the amount of rent you expect the property to receive.
The property investment calculator uses this to work out your rental income and the property's cashflow.
Vacancy – This is how much time you expect the property to be vacant per year. During these weeks the property is assumed not to be producing rental income.
A property won’t necessarily be rented every week of the year, so allowing for vacancy gives you a more realistic estimate of the rental income you may actually receive.
Show figures in today’s dollars – If selected, the calculator adjusts future figures to show their equivalent value in today’s dollars.
This can make it easier to understand what future income and expenses are really worth after accounting for inflation.
The property investment calculator also asks you to enter the ongoing costs of owning the property. These include:
Rates – These are the council rates you expect to pay on the property each year.
Insurance – This is the annual cost of insuring the property.
Maintenance – This is an allowance for repairs and maintenance you expect to have to pay for over time.
The amount can vary significantly between properties. This is why it’s useful to enter an estimate specific to the property you’re analysing.
For instance, a New Build house may only need $750 of maintenance per year, but an older house may need $3,000 in maintenance per year.
Other – This is where you can include other ongoing costs that aren’t covered by the other categories.
Property management – If you use a property manager, enter their fee as a percentage of the rent collected, excluding GST.
This allows the calculator to account for the cost of having someone manage the property for you.
The mortgage is one of the biggest factors affecting a property’s cashflow. These are the factors to consider when calculating your potential returns:
Interest rate – This is the interest rate you expect to pay on the mortgage.
Interest rates will change, so you can adjust this figure to see how sensitive the investment is to different interest-rate scenarios.
Loan term – This is the length of the mortgage. This is only needed if you use a Principal and Interest mortgage.
Repayment type – You can choose between principal and interest (P&I) and interest only.
With a principal-and-interest mortgage part of each repayment goes towards paying down the loan.
With an interest-only mortgage your repayments initially cover the interest without reducing the principal.
This can make a significant difference to the property’s cashflow and the amount of debt remaining over time.
The calculator starts with some default assumptions about how the investment might perform in the future.
Important: These are not predictions. They’re simply the starting figures used when you first open the calculator.
You can change these assumptions to test different scenarios.
These are our assumptions as of August 2026:
The important thing to remember is that you can change any of these figures to test different scenarios.
For example, you might want to see what happens if property prices grow 3% rather than 5%, or if rents increase by only 2% a year. You could also increase the interest rate to see how the investment performs if borrowing costs are higher.
The most important thing to understand about a property investment calculator is that it doesn’t predict the future.
It takes the information you give it and calculates what would happen if those assumptions played out.
That’s useful because it lets you ask questions like:
This is why you shouldn’t just enter your numbers once and look at the final return.
Try different scenarios.
However, economist Ed McKnight warns about being overly optimistic.
He says: “I get it’s tempting to assume interest rates will fall quickly or property prices will keep growing strongly. But a realistic interest-rate assumption matters because you’ll have to pay the mortgage whether or not your property grows in value. I’d rather see investors use a realistic rate and conservative growth assumption … that way you can be pleasantly surprised if things turn out better.
“However, you also need to make sure you are not too pessimistic. If you are overly conservative, then you can needlessly scare yourself off investing. The only guarantee in investing is that if you do nothing, you get nothing.
“That’s why I encourage investors to be realistic. Sure, stress test a downside scenario, but also consider an upside scenario too.”
Once you’ve entered your numbers and assumptions, here’s what the calculator shows you.
This tells you whether the property is expected to get enough rent to cover its ongoing costs and mortgage repayments in the first year.
If the number is negative, you’ll need to contribute money to the investment.
For example, if the calculator shows -$56 per week, that means you’d need to top up the property by about $56 a week (approximately $2,917 over the year).
This is sometimes known as negative gearing.
This shows how the property’s value and the amount you owe on the mortgage are expected to change over time.
The property’s value is based on the property growth rate you’ve entered.
The mortgage figure shows how much you are expected to owe at each point in time. With a principal-and-interest loan, the mortgage balance should reduce as you pay off the principal.
With an interest-only loan, the balance generally won’t go down during the interest-only period.
The difference between the property’s value and the mortgage is your equity in the property.
The calculator also shows the potential return over the timeframe you’ve selected.
The multiple shows how much your investment has grown relative to the cash you’ve put into it.
The percentage shows the return you’ve made relative to the cash you’ve invested.
So, if the calculator shows 4.0x and +295% on cash in, it means the modelled outcome is four times the amount of cash you’ve put into the investment. That represents a 295% return on that cash.
It’s important to remember this is a projection based on the assumptions you’ve entered. Change any of these assumptions and the result will change too.
The figures produced by this Property Investment Calculator are estimates. They are based on the information and assumptions you enter.
The actual performance of an investment property will vary.
Your property might grow by more than your assumed growth rate one year and less the next. You might have a period without a tenant or your insurance bill could increase unexpectedly.
The point of the calculator isn’t to tell you exactly what will happen.
It’s to help you understand the relationship between the purchase price, deposit, mortgage, rental income, expenses and long-term growth.
Once you understand those numbers you can make a much more informed decision about whether an investment makes sense for you.
This calculator is for general information only. It’s not financial advice. See here for details about our Financial Advice Provider Disclosure. So Opes isn’t telling you what to do with your own money.
We’ve made every effort to make sure the calculator and its assumptions are reasonable and accurate. But calculators rely on estimates and inputs you provide, and the results won’t be right for everyone. Make sure you do your own research or talk to a financial adviser before making any investment decisions.
You might like to use us or another financial adviser.
