Work out your home-loan repayments, total interest and payoff time — then see how extra repayments, an offset account and a rate change move the numbers.
This tool estimates the regular repayment on an Australian home loan and shows the bigger picture most lenders bury: the total interest you’ll pay, the total cost of the loan, and how long it actually takes to clear. It then lets you stress-test the loan against the three levers that matter most in real life — extra repayments, an offset account, and a change in interest rates. Everything recalculates the instant you change an input, and you can save a shareable link so you don’t lose your scenario.
For a principal-and-interest loan, the repayment comes from the standard amortisation formula used by every Australian lender:
M = P × r × (1 + r)ⁿ ÷ ((1 + r)ⁿ − 1)
Here P is the loan balance, r is the periodic interest rate (your annual rate divided by the number of payments a year — 12 for monthly, 26 for fortnightly, 52 for weekly), and n is the total number of repayments (years × payments per year). If the rate is 0%, the formula simplifies to M = P ÷ n. Each period the lender charges interest of balance × r; the rest of your repayment (M − interest) reduces the principal. As the balance shrinks, the interest portion falls and the principal portion grows — that’s why early repayments are mostly interest and late repayments are mostly principal.
Interest only (IO): the repayment is simply balance × r — you pay the interest and nothing else, so the balance never moves. Repayments are lower, but you pay more interest overall and the debt is still there at the end of the IO period.
Extra repayments are added to every scheduled payment and applied entirely to principal. We then re-run the loan period by period until the balance hits zero, which gives you the new (shorter) payoff time and the interest you’ve saved versus the standard schedule.
Offset: a 100% offset account reduces the balance interest is charged on. We treat the offset as a constant amount subtracted from your balance each period (interest = max(balance − offset, 0) × r), while keeping your repayment the same — so the freed-up money attacks the principal faster. Real offsets fluctuate daily with your spending, so treat this as the “if the balance stays put” case.
The rate-change slider recomputes the scheduled P&I repayment at −0.50%, −0.25%, your rate, +0.25% and +0.50%, and shows the dollar difference per period — handy for sizing up an RBA move or a lender’s out-of-cycle change before it lands.
This is an estimate, not a quote. It assumes a single fixed rate for the whole term, even though most Australian loans are variable and will move many times over 25–30 years. It ignores establishment fees, ongoing or monthly account fees, lenders mortgage insurance (LMI), redraw rules, and the rate “revert” jump that hits when a fixed or interest-only period ends. It also assumes every repayment is made in full and on time, and that the calendar is regular (lenders calculate daily interest on the actual number of days, so your statements will differ by a few dollars). For fixed loans, check your extra-repayment cap — many limit you to a few thousand dollars a year before break costs apply.
A few things are distinctly local. Offset accounts are nearly universal here and are one of the most tax-effective ways to get ahead, because the “return” (interest saved) isn’t taxable income the way savings-account interest is. Fortnightly repayments are a quiet accelerator: because there are 26 fortnights but only 12 months, paying half the monthly figure each fortnight squeezes in the equivalent of 13 monthly payments a year — one extra month, every year, straight off your principal. Watch the framing, though: if a repayment is calculated as the true fortnightly equivalent (monthly ÷ 2.17), that bonus disappears. Finally, your loan rate is not the RBA cash rate. The cash rate sat at 4.35% in June 2026; actual owner-occupier variable rates were roughly 5.9%–6.9%, because lenders add a margin. Always model your real contract rate, and stress-test a rise — the slider above is built for exactly that.
General information only — an estimate, not financial, tax, credit or legal advice. Figures current as at FY2025-26, reviewed June 2026. Confirm with the ATO / your lender / the relevant state revenue office.
Sources: Reserve Bank of Australia — Cash Rate Target (4.35%, June 2026) and Lenders’ Interest Rates (average owner-occupier variable rate); Canstar interest-rate outlook 2026. Repayment formula: standard loan amortisation.