Property & Home · Comprehensive loan plan

Mortgage Optimiser Calculator — Pay less. Finish sooner.

Combine offset savings, regular extra repayments, a one-off lump sum and an interest-only period. See exactly how each lever cuts interest and shortens the loan against the do-nothing baseline.

What you enter

  • Loan amount
  • Interest rate
  • Loan term
  • Repayment frequency
  • Interest-only period
  • Offset balance today
  • Add to offset each month
  • Extra per repayment
  • One-off lump sum
  • Lump sum in year

How this is calculated

This is a full loan simulation, period by period. Interest is charged each period on the loan balance minus your offset balance; your contracted repayment stays fixed, so everything the offset saves in interest goes to principal instead. On top we layer recurring extra repayments, monthly offset growth, an optional one-off lump sum in the year you choose, and an optional interest-only period — then compare against the do-nothing baseline.

Common questions

How does an offset account actually save interest?

Interest is calculated daily on (loan balance − offset balance). Money in offset works exactly like money paid off the loan — but stays accessible. $40,000 in offset against a 6% loan saves $2,400 a year in interest, tax-free, which beats most savings accounts after tax.

Should I use a lump sum for the loan or invest it?

Paying down a 6% loan is a guaranteed, tax-free 6% return. Investing might beat that, but with risk and tax on gains. The honest answer depends on your rate, tax bracket and risk tolerance — this calculator shows the loan side of the comparison precisely.

Why does an interest-only period cost so much?

During interest-only years the principal doesn't move, so you pay interest on the full balance for longer, and the remaining principal must then amortise over a shorter time — raising later repayments. It buys cash-flow now at a significant lifetime cost, which the comparison quantifies.

How does it rank?

Once you have your result, see how your number compares against your demographic with our full money rank — by age, sex, state and household composition.

Methodology & data

PRINCIPAL & INTEREST · INDICATIVE. Australian context, FY 2026–27 tax brackets by default (15% lowest marginal rate from 1 July 2026) with a financial-year selector on tax calculators. Calculations are indicative and based on simplified public models — not personal financial, tax or legal advice. See the full disclaimer.

Primary data sources

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