Skip to content

Mortgage Repayment Calculator

Calculate home loan repayments weekly, fortnightly or monthly, with a full amortisation schedule, total interest, payoff date and every assumption on show.

AustraliaScheduled modelClass B · rule-based estimateNo statutory rules requiredMethodology
AUD

Repay interest only for the first years, then principal and interest.

Enter the loan amount, rate and term to see the repayment, total interest and the full schedule.

Summary

The repayment comes from the §13.5 closed form, then every period is written out as a ledger row so the interest total, the payoff date and the schedule all come from the same run.

Working

  1. §13.5 payment: the scheduled repayment solves P = B·i ÷ (1 − (1 + i)^−n) from the balance B, the periodic rate i and the remaining periods n.
  2. §13.7 recurrence: each period: interest = accruing balance × i, then closing = opening + interest + fees − payment − extra repayment.
  3. §13.9 offset: interest accrues on max(0, balance − offset × effectiveness), floored at zero; offset cash is never a principal repayment.
  4. §12.5.8 reconciliation: the ledger identity is checked on every period. A reconciliation failure invalidates the result rather than warning about it.

Assumptions

  • Interest accrues once per repayment period on the payment-period ledger. Daily accrual is not modelled at P0.
  • The first repayment falls on 1 October 2026; every date in the schedule follows from that and the repayment frequency.
  • The rate is held constant except where a dated rate-change event moves it.
  • Weekly, fortnightly and monthly frequencies use 52, 26 and 12 periods per year.

Limitations

  • Lender daily accrual, transaction timing, fee timing and rounding can differ from this model; compare the settings with your loan contract and statements.
  • Redraw availability, offset eligibility conditions, break costs and any lender fee that was not entered are not modelled.
  • Amounts beyond the entered term are not projected; a balance left unpaid at term is reported rather than extended.

Common questions

How are mortgage repayments calculated in Australia?

The level repayment is solved from the loan amount, the periodic interest rate and the number of repayments left in the term, then this calculator builds the whole schedule repayment by repayment rather than stopping at the formula. Each period charges interest on the balance carried into it, subtracts the repayment, rounds to the cent and carries the remainder forward, so the interest and payoff figures come from the ledger itself. The methodology page sets out the formulas and the working panel shows every assumption.

Does paying fortnightly instead of monthly reduce interest?

Changing the repayment frequency changes the schedule, and the calculator recomputes it from scratch at weekly, fortnightly or monthly rather than scaling one answer into another. Two effects are mixed together: interest is charged over shorter periods, and a repayment set at half the monthly amount every fortnight pays more per year than twelve monthly repayments. Switch the frequency field to see both the repayment and the lifetime interest recalculated on the new schedule.

What is the total cost of a mortgage?

Total paid is every scheduled repayment added up plus any fees you enter, and total interest is that figure less the amount borrowed. The calculator reports both alongside the payoff date and the number of repayments, so the headline repayment is never the only number on screen. An annual package fee, if you enter one, is added to the schedule rather than quoted separately.

Why is the final mortgage repayment a different amount?

Rounding each repayment to the cent leaves a small residue that accumulates over hundreds of periods, so the last repayment is adjusted to close the balance at exactly zero. The calculator makes that adjustment explicitly and caps it, rather than letting a rounding drift accumulate into the totals. You can see the closing balance move to zero in the schedule.

Does the calculator model rate changes, offsets or extra repayments?

This calculator holds the rate constant for the whole term so the schedule is comparable end to end. Dated rate changes, offset balances, extra repayments and fee events are modelled on the full scheduled ledger in the mortgage simulator, which reconciles the balance on every period. Use this page for a clean baseline and the simulator when events land on specific dates.

Related calculators

All Property and mortgage calculatorsHow the Mortgage Repayment Calculator worksAll calculators