What will this loan actually cost you?
Most online repayment calculators get the maths wrong by thousands. They miss daily interest, offset savings, and the gap between true fortnightly payments and the version banks use. This one works through every day of your loan and shows you the real total.
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Your headline numbers
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How we got this
Working out the math…
Why other repayment calculators are wrong
It's not a small problem. The repayment calculator is the most-used finance tool on the internet — and almost every consumer-facing version of it gets the maths wrong by thousands of dollars over the life of a 30-year loan. Three sources of error account for most of the gap:
- Monthly interest shorthand. Most calculators compute interest as balance × (annual_rate ÷ 12) per month. The accurate calculation is daily: interest accrues on the actual outstanding balance (less offset) every calendar day at annual_rate ÷ 365, and only capitalises at month-end. Across a 30-year loan the day-count difference is real — months are not equal-length, and the timing of repayments within a month moves the daily-balance trajectory.
- Offset modelled as a flat balance reduction. When calculators bother to handle offset at all, most subtract the offset balance from the loan balance and apply the same monthly-shorthand interest formula. The accurate version applies offset against the daily balance — which is what your lender's actual loan ledger does. The differences compound across 30 years.
- Bank-fortnightly = "save four years." The marketing claim is technically correct but for the wrong reason. Bank-style fortnightly = monthly payment ÷ 2, paid every 14 days. That's 26 payments × half-monthly = 13 monthly equivalents per year. You're not benefiting from compounding magic — you're making an extra month of payments per year. True fortnightly (monthly × 12 ÷ 26) doesn't shave years off the loan; bank-style does, but only because you're paying more.
The calculator above runs your specific numbers through a day-by-day simulation. The "what other calcs miss" callout below the result tells you exactly how much the typical bank tool is overstating or understating against the accurate run.
What this calculator does NOT model (yet)
- Rate changes mid-loan. Fixed periods that revert to variable, RBA cuts, refinances. v1 holds rate constant; v2 will accept a schedule.
- Fluctuating offset balances. v1 uses the constant balance you input. Real offsets move with pay cycles, big purchases, savings sweeps. The constant-balance model is conservative if you'd otherwise spike the balance during high-balance periods of the loan.
- Lender fees. Annual package fees ($395 typical), monthly account fees, valuation fees. None modeled. The loan-level number above is interest only.
- Redraw events. If you make extras and pull them back, you've effectively changed your offset balance retroactively. v1 assumes extras stay paid.
- Tax effects. Investment loan interest deductibility, debt recycling, negative gearing. We surface these on file rather than as headline calculator output.
For a deal-binding number with all these effects layered in — your actual lender's pricing, your actual fees, your actual offset behaviour — the calculator output is the start of the conversation, not the end.
Bottom line
Three minutes of accurate maths is worth more than ten minutes of sloppy maths plus a confident-sounding rule of thumb. The calculator above does the accurate version. The rest is your specific lender, your specific structure, and your specific cash-flow rhythm — which is what the broker conversation is for.