Take a $650,000 home, 20% down ($130,000), and a $520,000 loan on a variable rate of roughly 6.19% (RBA cash rate context plus a typical lender margin) over 25 years — the monthly payment lands around $3,413. What matters more than that single number is what happens to it every time the Reserve Bank of Australia moves the cash rate, because most Australian mortgages are variable, not fixed — a genuinely different default to the fixed-rate norm in the US and UK.
Variable is the Default, Not the Exception
The large majority of Australian home loans are on variable rates, meaning the interest rate — and therefore the monthly payment — moves whenever the lender adjusts pricing, which usually tracks RBA cash rate decisions fairly closely, though not always exactly in lockstep. Fixed-rate options exist, typically for 1-5 year terms, but even those eventually revert to a variable rate once the fixed period ends — there's no long-term fixed product equivalent to a US 30-year fixed.
The Math
Standard Australian mortgage repayments use monthly compounding:
Where P is the loan amount, r is the monthly interest rate (annual ÷ 12), and n is the number of monthly payments — but unlike a fixed-rate loan elsewhere, r itself can change at any point during the loan if the lender reprices.
Worked Example
| Input | Value |
|---|---|
| Property price | $650,000 |
| Deposit (20%) | $130,000 |
| Loan amount | $520,000 |
| Rate | ~6.19% variable |
| Term | 25 years (300 payments) |
| Monthly Payment | ≈ $3,413 |
Common Mistakes
Borrowers frequently budget to their current payment without stress-testing it against a rate rise — since the loan is variable by default, today's number isn't a reliable long-term figure the way a US 30-year fixed payment is.
Borrowers also assume a fixed-rate period behaves like the US model — locking a rate for 1-3 years feels similar, but the loan reverts to variable afterward, often onto a less competitive rate than what's available to new customers, which is worth actively managing rather than letting happen automatically.
A third mistake: not accounting for lender-specific rate movements. RBA cash rate changes don't always translate one-for-one into a lender's variable rate — lenders can (and sometimes do) move independently of the RBA, in either direction.
Where This Calculator Has Limits
It uses a single point-in-time rate — since the loan is variable, the true lifetime cost depends on a rate path that's impossible to predict with certainty. It also doesn't include Lenders Mortgage Insurance, which applies for this buyer only if the deposit were under 20% (see our LMI Calculator for that scenario).
Frequently Asked Questions
Are fixed-rate mortgages common in Australia?
They exist, typically for 1-5 year terms, but the market default is variable — most borrowers hold a variable-rate loan for the majority of their mortgage's life.
Does the RBA directly set my mortgage rate?
No — the RBA sets the cash rate, a wholesale benchmark. Lenders set their own variable rates, which usually track the cash rate closely but aren't legally required to move by the same amount.
What happens when my fixed-rate period ends?
The loan reverts to a variable rate, often the lender's standard variable rate, unless you actively negotiate, refinance, or lock in a new fixed term beforehand.
Does a bigger deposit still help on a variable-rate loan?
Yes — it reduces the loan amount and can avoid Lenders Mortgage Insurance above 20% down, independent of whether the rate itself is fixed or variable.
Can I switch between fixed and variable during my loan?
Usually yes, though switching typically involves refinancing internally with your lender or externally, and may carry fees or, if breaking a fixed term early, break costs.
Related Tools
LMI Calculator · Offset Account Calculator · Affordability Calculator
Educational content, not financial advice. Rates and figures are illustrative and change regularly with RBA decisions and lender pricing — confirm current numbers with a licensed Australian mortgage broker or lender. Written by the MortgagePro Global team.