Home Loan Repayments in Australia: What the Calculators Don't Show You
LMI, stamp duty by state, offset accounts, and how rate rises actually hit your repayments — what the standard mortgage calculators leave out, with worked examples.
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Try Finance Calculator →I bought my first property in Adelaide in 2022, right as the rate cycle turned. Between signing contracts and settlement, the RBA had already made two moves. I spent a lot of time with calculators that told me my repayments would be $X — and then reality was more complicated.
The standard online calculators give you a good approximation of monthly repayments. What they don't show you is the full picture of what homeownership costs, how repayments respond to rate changes, and which strategies actually reduce what you pay over the life of the loan. This post covers the gaps.
What the calculators typically show
Most mortgage calculators take three inputs — loan amount, interest rate, and loan term — and return a monthly repayment figure using the standard EMI formula. That number is accurate for what it represents: the regular principal-and-interest payment required to repay the loan at the stated rate over the stated term.
What it doesn't show: the cost to get to that repayment (stamp duty, LMI, legal fees), how the repayment changes when rates move, the effective rate reduction from an offset account, or the total interest cost over 30 years.
Let me work through each of these.
The upfront costs most calculators ignore
Stamp duty by state
Stamp duty (now called "transfer duty" in some states) is calculated on the purchase price and varies significantly by state. On a $600,000 purchase in 2026, the approximate duty payable is:
| State | Duty (approx.) | First home buyer concession |
|---|---|---|
| NSW | $22,490 | Full exemption ≤ $800K |
| Victoria | $31,070 | 50% concession ≤ $600K |
| Queensland | $12,850 | Full exemption ≤ $550K |
| South Australia | $26,830 | No general concession |
| Western Australia | $22,190 | Full exemption ≤ $430K |
| ACT | $23,280 | Concession schemes available |
These figures change with state budgets. Always verify with your state's revenue office — for SA that's the RevenueSA website{:target="_blank"}, for NSW the Revenue NSW portal{:target="_blank"}.
In South Australia, first home buyers get a $15,000 First Home Owner Grant on new homes rather than a stamp duty concession — which is less valuable than the exemptions available in other states, a point I wish I'd understood better before signing.
Lenders Mortgage Insurance (LMI)
LMI applies when your deposit is below 20% of the property value. It's a one-off premium that protects the lender (not you) if you default — but you pay it.
On a $500,000 purchase with a 10% deposit:
- Loan amount: $450,000 (90% LVR)
- Approximate LMI premium: $8,500–$12,000 depending on the insurer and lender
Most lenders allow you to capitalise LMI into the loan rather than paying upfront, which is convenient but expensive — you pay interest on the LMI premium for the entire loan term.
The calculation that matters: at 6.2% over 30 years, $10,000 of capitalised LMI costs approximately $21,000 in total (principal + interest). That $10,000 "free" capitalisation is actually $21,000 over the life of the loan.
How rate rises actually hit repayments
This is the worked example I wish I'd had when the RBA started hiking.
Scenario: $500,000 loan, 30-year term, principal and interest
At 6.20% annual rate:
- Monthly repayment: $3,067
After a 0.25% rise to 6.45%:
- Monthly repayment: $3,133
- Increase: $66/month, $792/year
After a second 0.25% rise to 6.70%:
- Monthly repayment: $3,200
- Total increase from start: $133/month, $1,596/year
At a $750,000 loan, scale those numbers by 1.5. A single 0.25% rise adds approximately $99/month; three rises add $299/month.
The RBA moved the cash rate 13 times in 2022–2023, from 0.10% to 4.35%. A $500,000 variable loan that started at approximately $2,000/month ended at approximately $3,000/month. That's a $1,000/month increase that no standard calculator prepared borrowers for.
You can run rate-rise scenarios yourself with the home loan calculator — enter your loan amount and try different rates to see exactly what each 0.25% movement does to your monthly repayment.
Offset accounts: the calculator rarely includes this
An offset account is a transaction account linked to your mortgage. Every dollar in the offset reduces the balance on which interest is charged.
$600,000 loan at 6.2% — effect of offset account:
| Offset balance | Effective loan | Annual interest saving |
|---|---|---|
| $0 | $600,000 | — |
| $20,000 | $580,000 | $1,240/year |
| $50,000 | $550,000 | $3,100/year |
| $100,000 | $500,000 | $6,200/year |
The offset isn't magic — it's just your savings doing double duty. But the effective return is your mortgage rate (6.2% in this example), risk-free, tax-free. Compared to a savings account earning 4–5% gross (taxed), the offset is meaningfully better for most borrowers.
The catch: offset accounts are predominantly available on variable rate loans. Most fixed rate products either don't offer an offset or limit it to partial offset on a portion of the loan. If you're considering fixing your rate, calculate what you'd lose in offset benefit before committing.
For the mechanics of compound interest underlying all of this, how to calculate compound interest by hand walks through the formulas with worked examples.
Principal and interest versus interest-only
Interest-only loans are common for investment properties and are worth understanding even if you're buying a home to live in.
$500,000 loan at 6.2%:
| Repayment type | Monthly repayment | Loan balance after 5 years |
|---|---|---|
| Principal + interest (30yr) | $3,067 | $455,000 |
| Interest-only (5yr then P+I) | $2,583 | $500,000 |
| P+I after IO period ends | $3,264 | — |
During the interest-only period, repayments are lower ($484/month lower in this example). After 5 years, you've paid $29,040 less in repayments — but you still owe the full $500,000.
When the IO period ends, your loan reverts to P+I with only 25 years remaining instead of 30. The monthly repayment jumps from $2,583 to $3,264 — $681 higher than if you'd been on P+I from the start.
Over the full life of the loan, the IO borrower pays approximately $38,000 more in total interest than the P+I borrower, despite the lower early repayments.
Interest-only is a cash-flow tool for investors who want to maximise rental yield and deductibility in the early years. For owner-occupiers, it's almost always more expensive than it first appears.
What the RBA's cash rate changes actually filter through
One thing that confuses people: the RBA cash rate and your mortgage rate aren't the same number.
The cash rate is the overnight interbank lending rate — the rate at which banks lend to each other. Your mortgage rate is the cash rate plus a margin the bank sets. When the RBA moves the cash rate by 0.25%, lenders typically (but don't always) pass the full change on within a few days.
The actual mortgage rate you pay is: cash rate + bank margin + any risk premium for your LVR and credit profile. The margin varies by lender and product. At the peak of the 2022–2023 cycle, the cash rate was 4.35% and typical variable mortgage rates were 6.0–7.0% — a margin of 1.65–2.65%.
Understanding this means you can monitor the RBA's Board decisions{:target="_blank"} and estimate your rate change before your lender sends you a letter.
The strategy that actually reduces total interest paid
The most effective lever most borrowers have is extra repayments on a variable rate loan.
On a $600,000 loan at 6.2% over 30 years:
- Standard repayments: total interest of approximately $390,000
- Extra $300/month: saves approximately $97,000 in interest and 7 years off the loan
- Extra $500/month: saves approximately $142,000 in interest and 10 years off the loan
These aren't marginal differences. But they require a variable rate loan with no restrictions on extra repayments, and enough income buffer to sustain the extra payments through rate rises.
For the fixed versus variable decision, fixed vs variable home loans in Australia 2026 covers the trade-offs in detail.
- Stamp duty and LMI can add $20,000–$50,000 to the upfront cost of buying, which most repayment calculators don't include
- A single 0.25% rate rise adds approximately $66/month on a $500,000 loan — multiple rises compound quickly
- An offset account earns your mortgage rate as a risk-free, tax-free return on your savings; this is hard to beat
- Interest-only repayments look cheaper short-term but typically cost $30,000–$50,000 more in total interest over the loan's life
- Extra repayments of $300–$500/month on a $600,000 loan can save six figures in interest over 30 years
FAQ
What is LMI and when does it apply in Australia?
Lenders Mortgage Insurance (LMI) is a one-off premium paid by the borrower that protects the lender if you default. It applies when your deposit is less than 20% of the property's value. On a $500,000 purchase with a 10% deposit, LMI is typically $8,000–$12,000. You can pay it upfront or capitalise it into the loan, though capitalising increases your total interest paid significantly — a $10,000 LMI premium costs approximately $21,000 in total interest at 6.2% over 30 years.
How much does stamp duty cost in each Australian state?
On a $600,000 purchase in 2026: NSW approximately $22,490; Victoria approximately $31,070; Queensland approximately $12,850; South Australia approximately $26,830; Western Australia approximately $22,190. First home buyer exemptions and concessions vary significantly by state — NSW fully exempts first home buyers on properties up to $800,000. Always verify current figures with your state's revenue office before making financial decisions.
How does a 0.25% rate rise actually affect monthly repayments?
On a $500,000 loan at 6.20% over 30 years, the monthly repayment is approximately $3,067. After a 0.25% rise to 6.45%, it becomes approximately $3,133 — an increase of about $66 per month. On a $750,000 loan the same rise adds approximately $99 per month. Multiple rises compound: two 0.25% rises on a $500,000 loan add approximately $133 per month compared to the starting rate.
Does an offset account really make a meaningful difference?
Yes, for borrowers who maintain a consistent balance. On a $600,000 loan at 6.2%, $50,000 in an offset account saves approximately $3,100 in the first year. The offset works like a guaranteed, tax-free return equal to your mortgage rate — which is difficult to beat with any comparable savings product. The catch: offset accounts are predominantly available on variable rate loans, which is a key consideration when comparing fixed versus variable products.
What's the difference between principal and interest vs interest-only repayments?
Principal and interest repayments reduce your loan balance with every payment, so you build equity and the loan ends at the agreed term. Interest-only repayments pay only the interest charge — your balance doesn't decrease during the IO period. When the IO period ends, repayments jump significantly (typically 15–25% higher than standard P+I), and you'll pay significantly more total interest over the loan's life. Interest-only is primarily a cash-flow management tool for investors, not a cost-reduction strategy.