Weekly vs Fortnightly vs Monthly Mortgage Repayments

Short answer

Switching from monthly to fortnightly or weekly repayments, on its own, saves only a small amount of interest, because Australian home loans charge interest daily on the balance no matter how often you pay. The large savings people quote come from one specific method: when your lender sets each fortnightly repayment at half your monthly amount, you make the equivalent of 13 monthly payments a year instead of 12, which is really an extra repayment in disguise. So frequency matters far less than how much you pay each year.

How repayment frequency actually works

Most Australian lenders calculate interest daily on your outstanding balance and charge it monthly. Paying more often nudges your balance down a few days sooner each cycle, so there is a genuine but tiny interest saving from weekly over fortnightly over monthly. It usually comes to only a few hundred dollars over a 30-year loan.

The headline "pay fortnightly and save tens of thousands" claim relies on a different mechanism. There are 12 months but 26 fortnights (and 52 weeks) in a year. If your lender simply halves your monthly repayment and charges it every fortnight, you pay 26 × half = 13 monthly payments' worth each year, an extra month's repayment annually. That extra money goes straight to principal, which is what shortens the loan and slashes interest.

The catch is that it only works if the per-payment amount is half the monthly figure, not a smaller "true fortnightly" amount recalculated to fit 26 payments. Moneysmart frames this as paying off your loan faster by making extra repayments, which is exactly what the half-monthly trick is.

Worked example: a $600,000 loan at 6% over 30 years

True Loan uses true-periodic maths. It re-amortises each frequency over its own number of periods (annual rate ÷ periods per period, 30 × periods total). On that like-for-like basis:

Frequency	Per payment	Payments/yr	Total interest	Saving vs monthly
Monthly	$3,597.30	12	~$695,029	—
Fortnightly	$1,659.50	26	~$694,408	~$621
Weekly	$829.58	52	~$694,142	~$887

So a like-for-like frequency change saves under $1,000 over 30 years. The monthly repayment of $3,597.30 matches True Loan's standard figure.

Now apply the half-monthly trick. Pay $1,798.65 per fortnight (half of $3,597.30) instead of the "true" $1,659.50:

• 26 × $1,798.65 = $46,765 a year vs $43,168 for monthly, about one extra monthly repayment.
• The loan clears in roughly 24.5 years instead of 30.
• Total interest drops to about $546,000, a saving of roughly $149,000.

The savings come from the extra $3,600 a year ($300/month), not from the calendar. You could get the same result by keeping monthly repayments and adding ~$300/month.

Model this in True Loan

Open the True Loan calculator and enter the loan amount, rate and term, then change the Repayment frequency between monthly, fortnightly and weekly to see the true-periodic difference for yourself.

To model the half-monthly "13th payment" effect honestly, keep frequency on monthly and use the Extra repayment ($/month) input; set it to around $300 to replicate paying half the monthly amount fortnightly. Watch the total interest and the payoff date in the timeline. (Extra repayments and the Offset balance input are separate fields. An offset account works differently but reduces interest in a similar way.)

To compare two strategies side by side, say "monthly, no extra" against "monthly + $300 extra", use the comparison tool; every scenario is shareable via URL.

Common questions and mistakes

Does paying weekly beat fortnightly? Only marginally on a like-for-like basis (see the table). The frequency itself is a rounding error; what you pay per year is what counts.

Will my lender automatically use the half-monthly method? Not always. Some set "true" fortnightly/weekly amounts that don't add up to a 13th payment. Ask your lender how the amount is calculated; if it isn't exactly half the monthly figure, you won't get the big saving without adding extra repayments.

Does more frequent paying lower my repayment? No. In True Loan, extra payments shorten the term, not the scheduled repayment. See the falling total interest on a $600k loan.

Is fortnightly always better than an offset? They're different tools. The half-monthly trick is essentially forced extra repayments; an offset keeps your money accessible while still reducing interest. Model both before deciding.

These figures are estimates generated by True Loan's calculator. Check your loan contract and official sources such as moneysmart.gov.au; this is general information, not financial advice.