Mortgage repayment calculator

This works out what a home loan really costs per month, fortnight or week, and the total interest over the life of the loan. It is the same amortisation maths any bank’s home loan repayment calculator runs, with the working shown. The rate starts at the Reserve Bank’s average for new owner-occupier variable loans in August 2026 (6.2%), so the first figure you see is a realistic one; put in the rate your lender quotes and everything below the form follows it.

Repayments across a range of rates

Monthly repayment and lifetime interest on a $600,000 loan over 30 years — and if your current rate sits at the top of this table, the refinance calculator prices the switch:

Repayments by loan size

A quick loan repayment calculator table — 6.2% over 30 years, from the same tested engine:

Wondering what a lender would actually let you borrow? That's a different question — the borrowing power calculator answers it with the 3% APRA buffer applied.

Where the money goes — the shape of amortisation

The repayment never changes, but what it buys does. The very first $3,674.81 on the $600,000 example is $3,100 of interest and only $574.81 of actual debt reduction — the bank gets paid first, and the loan barely moves. Each month the balance shrinks a little, so a little less interest accrues, so a little more of the same repayment lands on principal. The compounding of that tiny shift is the whole story of a mortgage: on this loan it takes until month 227 — 18 yrs 11 mos in — before even half your repayment is paying off the house rather than renting the money.

This is also why anything extra you pay early punches so far above its weight. A dollar of principal killed in year two stops compounding against you for nearly three decades — the extra repayment calculator and the offset calculator both run on exactly this mechanism.

Interest-only, quantified

Interest-only looks cheaper because it is — for a while. On the $600,000 example the IO repayment is just $3,100 a month ($575 less than principal-and-interest). But after a 5-year IO period you still owe the entire $600,000, now amortising over the remaining 25 years at $3,939.49 a month — $265 more than if you'd paid principal from day one. Total interest over the loan's life: about $767,848 against $722,933 — roughly $45,000 for the privilege of five cheap years. Investors do it anyway for tax and cash-flow reasons (interest is deductible on a rental, principal never is — see the negative gearing calculator); owner-occupiers rarely should.

The fortnightly trick, quantified

Genuine fortnightly amortisation saves almost nothing — the famous saving comes from a sleight of hand. Pay half your monthly repayment every fortnight and, because the year holds 26 fortnights but only 12 months, you quietly make thirteen months of repayments a year. On the $600,000 example that's equivalent to about $306 extra a month, which cuts 5 yrs 7 mos off the term and about $158,000 off the interest — from a change most budgets never feel. Any lender that lets you set your own repayment schedule lets you do this on day one.