By Catherine Mulholland, Otivo
There are 12 months in a year and 26 fortnights. That small arithmetic mismatch is the entire basis of one of the most repeated pieces of mortgage advice in Australia — switch to fortnightly repayments and you'll make an extra month's worth of payments each year without noticing. On a $600,000 loan at 6%, that quietly removes about five and a half years and roughly $149,000 in interest. The part almost nobody mentions is that it only works if your lender sets the payment up one particular way, and plenty don't. Here's the mechanic, and the question to ask before you switch.
Switching from monthly to fortnightly repayments works because 26 fortnightly payments at half the monthly amount equals 13 monthly payments a year instead of 12. On a $600,000 loan at 6% over 30 years, that cuts the term to about 24 years and six months and saves around $149,000 in interest. The benefit only applies if the fortnightly payment is set at half the monthly figure.
Why does paying fortnightly make a difference at all?
A monthly repayment schedule produces 12 payments a year. A fortnightly schedule produces 26.
If the fortnightly payment is set at exactly half the monthly one, the yearly total goes up. On a $600,000 loan at 6% over 30 years, the monthly repayment is about $3,598, so the fortnightly equivalent is about $1,799.
- Paid monthly: $3,598 × 12 = $43,176 a year.
- Paid fortnightly at half: $1,799 × 26 = $46,774 a year.
The difference is $3,598 — one extra monthly repayment, appearing each year without any change to the household budget beyond the timing of the transfers. Every dollar of that extra payment goes straight to principal, which reduces the balance interest is charged on for the remainder of the loan.
There's a smaller secondary effect too. Paying more frequently means the balance drops slightly sooner within each month, so a little less interest accrues along the way. It's real but modest — the thirteenth payment does most of the work.
What the extra payment actually buys
Run the same loan both ways and the gap is larger than most people expect.
- Monthly: 30 years, total interest about $695,000.
- Fortnightly at half the monthly amount: about 24 years and six months, total interest about $546,000.
That's roughly five and a half years and about $149,000, from a change that doesn't require earning more, spending less, or making any decision more difficult than filling in a form.
The effect is larger on bigger loans and longer terms, and larger again at higher interest rates, because there's more interest available to avoid.
The catch — how your lender calculates the fortnightly amount
Here's where the advice quietly fails for a lot of people.
Lenders set fortnightly repayments in one of two ways, and they produce completely different outcomes.
- Half the monthly repayment. 26 payments of $1,799, totalling $46,774 a year. This is the version that works.
- The annual total divided by 26. 26 payments of about $1,661, totalling $43,176 a year. Identical to paying monthly, in a different rhythm.
The second version isn't a trick, and it isn't hidden. It's simply a repayment frequency change with no extra payment attached, which is exactly what some borrowers want. But it delivers none of the benefit described above, and a borrower who switched believing they were shaving years off the loan would have no way of knowing from the repayment schedule alone.
The question worth asking a lender is direct: is the fortnightly repayment half the monthly repayment, or the annual amount divided by 26? The answer decides whether any of this applies.
Three things to check before switching
Most of the friction with this strategy is administrative rather than financial.
- Confirm how the lender calculates the fortnightly amount. Half the monthly figure, or annual divided by 26.
- Check whether extra repayments are allowed. Variable loans generally permit them. Fixed loans commonly cap extra repayments, and exceeding a cap can trigger a break cost — which means the fortnightly strategy may not be available on a fixed portion.
- Check the pay cycle lines up. Someone paid monthly who switches to fortnightly repayments will hit two months a year with three repayments falling in them. Worth knowing before it happens rather than after.
It's also worth noting the mechanic doesn't transfer to credit cards. Revolving credit doesn't have a fixed term to shorten, so paying more often changes the interest charged only slightly. What changes credit card interest is paying more in total.
Does the same logic apply to weekly repayments?
Yes, with the same condition attached and slightly less effect.
There are 52 weeks in a year, so a weekly payment set at a quarter of the monthly repayment produces the same thirteenth-month result — 52 × 25% of monthly equals 13 monthly payments. The additional benefit over fortnightly comes only from the marginally faster balance reduction within each month, which is small.
For most households the choice between weekly and fortnightly comes down to which one matches the pay cycle, since the point is to make the payment invisible.
Frequently asked questions
How much time does switching to fortnightly repayments save?
On a $600,000 loan at 6% over 30 years, about five and a half years, provided the fortnightly payment is half the monthly amount. The saving is proportionally similar on other loan sizes at the same rate and term.
Why doesn't fortnightly always work?
Because some lenders calculate the fortnightly repayment as the annual total divided by 26 rather than half the monthly figure. That version pays the same amount each year as monthly repayments and produces no reduction in the loan term.
Can I make fortnightly repayments on a fixed rate loan?
It depends on the loan. Fixed loans often limit extra repayments during the fixed period, and exceeding the limit can trigger break costs. Where a loan is split between fixed and variable, the strategy may still be available on the variable portion.
Is it better to pay fortnightly or make one lump sum extra payment a year?
Financially they're close, since both add roughly one extra monthly payment. Many Australians find the fortnightly version easier to sustain because it doesn't require finding a lump sum, though it also can't be paused as easily if money gets tight.
Does this work on personal loans and car loans?
The same arithmetic applies to any amortising loan with a fixed term, though the shorter terms mean the absolute saving is smaller. The same lender question applies.
Small structural changes tend to outperform good intentions, which is what makes this one worth ten minutes on the phone to a lender. Otivo provides regulated digital financial advice under AFSL and Australian Credit Licence No. 485665, and customers who follow its advice in full could be better off by $52,030 on average through faster debt repayment. Its debt advice looks at repayment options against household income and expenses, and the budget planner is a good place to see what's actually available before committing to a higher fortnightly figure. It's also worth reading alongside what a rate rise does to repayments, since both change the same number.
Sources
- ASIC MoneySmart, Pay off your mortgage faster
- Repayment, term and interest figures calculated on a $600,000 loan at 6%, 30-year original term, principal and interest, owner-occupier, fees excluded.
Disclaimer
The information in this communication is current as at August 2026 and has been prepared by Otivo Pty Ltd ABN 47 602 457 732, AFSL and Australian Credit Licence No. 485665. This content is general information only and has been prepared without taking into account your objectives, financial situation or needs. It is not personal financial or taxation advice and should not be relied on as such. Before acting on any information, you should consider its appropriateness having regard to your personal circumstances. This material must not be reproduced in whole or in part, or posted on any social media platform, without the prior written consent of Otivo Pty Ltd.