Question 1

How are mortgage repayments calculated in Australia?

Accepted Answer

Australian mortgage repayments are calculated using the standard amortisation formula: M = P × [r(1+r)^n] / [(1+r)^n − 1], where P is the principal, r is the periodic interest rate, and n is the total number of periods. Most lenders charge interest daily using the ACT/365 day-count convention, though this calculator uses monthly periods in estimate mode for simplicity. The difference is typically less than $50 per year on a standard home loan.

Question 2

What is the difference between P&I and interest-only repayments?

Accepted Answer

Principal and interest (P&I) repayments pay down both the loan balance and the interest each period, so your debt reduces over time. Interest-only (IO) repayments cover only the interest — your balance stays the same. IO loans have lower repayments initially, but you pay more interest over the life of the loan and face a 'payment shock' when the IO period ends and you switch to P&I repayments on the remaining balance over a shorter term.

Question 3

How do weekly or fortnightly repayments save me money?

Accepted Answer

Using the divide-monthly method (the Australian bank standard), your monthly repayment is divided by 2 for fortnightly or by 4 for weekly payments. Because there are 26 fortnights (not 24) and 52 weeks (not 48) in a year, you effectively make the equivalent of 13 monthly payments instead of 12. This extra payment goes directly to reducing your principal, saving you interest and shortening your loan term.

Question 4

What is the divide-monthly method vs true-period?

Accepted Answer

The divide-monthly method takes your monthly repayment and divides it by 2 (fortnightly) or approximately 4.33 (weekly). This is the standard method used by Australian banks. The true-period method recalculates the repayment using the actual number of periods per year (26 for fortnightly, 52 for weekly) in the amortisation formula. True-period results in a slightly lower per-period payment but does not produce the same accelerated payoff effect as divide-monthly.

Question 5

How much deposit do I need to avoid LMI?

Accepted Answer

You generally need a deposit of at least 20% of the property value (i.e., a loan-to-value ratio of 80% or less) to avoid Lenders Mortgage Insurance (LMI). LMI protects the lender — not you — if you default. With less than 20% deposit, LMI can add thousands to your upfront costs. Some government schemes like the Home Guarantee Scheme allow eligible first home buyers to purchase with as little as 5% deposit without paying LMI.

Question 6

What is the APRA serviceability buffer?

Accepted Answer

The Australian Prudential Regulation Authority (APRA) requires banks to assess your ability to repay at an interest rate at least 3 percentage points above the loan product rate. For example, if your loan rate is 6.30%, the bank must check you can afford repayments at 9.30%. This buffer protects borrowers against rate rises and is a key factor in how much you can borrow.

Question 7

How does an offset account reduce my interest?

Accepted Answer

An offset account is a transaction account linked to your home loan. The balance in the offset account is deducted from your loan balance before interest is calculated. For example, if you owe $500,000 and have $50,000 in your offset account, you only pay interest on $450,000. This reduces your total interest and can shorten your loan term — while keeping your funds accessible.

Question 8

Can I make extra repayments on a fixed-rate loan?

Accepted Answer

Most fixed-rate loans in Australia allow limited extra repayments — typically up to $10,000 to $30,000 per year without incurring break costs. Exceeding this limit or paying off the loan entirely during the fixed period may trigger early repayment fees (break costs), which can be substantial. Variable-rate loans generally allow unlimited extra repayments without penalty.

Question 9

What happens when my fixed rate expires?

Accepted Answer

When your fixed-rate period ends, your loan typically reverts to the lender's standard variable rate, which is usually higher than your fixed rate. This can cause a noticeable increase in repayments. Before your fixed period expires, you can negotiate a new rate with your current lender or refinance to another lender offering a more competitive rate.

Question 10

How accurate is this calculator?

Accepted Answer

This calculator uses the standard amortisation formula with monthly periods (estimate mode). It provides a close approximation of your actual repayments. Australian lenders typically calculate interest daily using the ACT/365 convention, which can produce slightly different results — usually within $10–$50 per year of the estimate. This calculator is designed for planning and comparison purposes and should not be relied upon as a substitute for a formal loan offer from a lender.

Frequency	Method	Payment	Annual Total	Extra / Year	Time Saved
Monthly	—	$3,706	$44,472	—	—
Fortnightly	Divide-monthly	$1,853	$48,178	$3,706	~4 years
Fortnightly	True-period	$1,712	$44,512	$40	~1 month
Weekly	Divide-monthly	$927	$48,204	$3,732	~4 years
Weekly	True-period	$856	$44,512	$40	~1 month

Mortgage Repayment Calculator Australia

How Mortgage Repayments Are Calculated

Full methodology

Why Daily Interest Accrual Matters

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Weekly vs Fortnightly vs Monthly Repayments

Offset Accounts vs Redraw Facilities

Offset Account

Redraw Facility

Deposit Size and Lenders Mortgage Insurance (LMI)

Mortgage Repayment Calculator FAQ

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