You've probably heard the advice: "Switch to fortnightly repayments and you'll knock years off your mortgage." It's one of the most repeated pieces of personal finance wisdom in Australia. It's also true at some banks and false at others — and the difference comes down to one line of arithmetic the bank chooses when setting up your repayment schedule. This article shows the maths, names which Australian lenders do which, and gives you the simpler alternative that works at any bank.
You can model your own loan side-by-side in the Calcula mortgage calculator — the rest of this article is the why behind the numbers it shows you.
The trick, in one paragraph
There are 12 months in a year but 26 fortnights. If your lender takes your monthly repayment and halves it, you pay that amount 26 times a year. Half a monthly payment paid 26 times is the equivalent of 13 monthly payments per year, not 12. That extra payment — one full month's worth, every year — is what reduces the principal faster and shaves years off the loan.
The catch is in the words "if your lender halves it." Many Australian lenders don't. They take the monthly figure, multiply by 12, and divide by 26 — which gives you exactly the same annual total as paying monthly. Same money out the door each year, just split into smaller chunks. The "trick" only works at lenders who use the divide-by-2 method.
The three definitions you'll see
| Definition | Formula | Annual total | Loan term effect |
|---|---|---|---|
| True fortnightly | Monthly ÷ 2, paid 26 times | 13 × monthly (one extra payment per year) | Significant — years off the loan |
| Equivalent fortnightly | (Monthly × 12) ÷ 26, paid 26 times | Exactly equal to 12 monthly | Essentially zero |
| True weekly | Monthly ÷ 4, paid 52 times | 13 × monthly (same as true fortnightly) | Marginally better than true fortnightly |
There is also "equivalent weekly" — (monthly × 12) ÷ 52 — which, like equivalent fortnightly, produces zero saving. The naming the banks use rarely makes this distinction obvious. You generally have to look at the calculator assumptions page or product disclosure to find out which method applies.
The maths on a $500,000 loan
A $500,000 P&I loan over 30 years at 5.66% has a monthly repayment of $2,889.34 (Calcula mortgage calculator for the working). At that loan, here's what each method produces:
| Scenario | Payment | Annual total | Loan term | Total interest | Saving vs monthly |
|---|---|---|---|---|---|
| Monthly | $2,889.34 | $34,672 | 30 years 0 months | $540,163 | — |
| Equivalent fortnightly | $1,333.54 | $34,672 | 30 years 0 months | ~$540,163 | nil |
| True fortnightly | $1,444.67 | $37,561 | 24 years 10 months | $431,350 | $108,812 |
| True weekly | $722.34 | $37,561 | ~24 years 10 months | ~$431,350 | ~$108,812 |
The true fortnightly column saves a hair under $109,000 in interest and trims 5 years 2 months off the loan. The equivalent fortnightly column saves nothing. Same loan, same rate — different bank method, six-figure difference over the life of the mortgage.
On a $750,000 loan the same logic produces about $163,000 of saving and the same 5-year-2-month reduction in term — the percentages scale roughly linearly.
Which Australian lenders use which method (as at May 2026)
This is the table that tells you whether your bank is doing you a favour or just rearranging the payment dates. The information comes from each lender's published calculator assumptions pages and from RateCity research (PropertyUpdate / RateCity, October 2023), cross-checked against current lender pages in May 2026.
| Bank | Method | True or equivalent? |
|---|---|---|
| Westpac | Divide by 2 | True fortnightly — saves interest |
| St.George (Westpac group) | Divide by 2 | True fortnightly — saves interest |
| Bank of Melbourne (Westpac group) | Divide by 2 | True fortnightly — saves interest |
| Bank of Queensland | Divide by 2 | True fortnightly — saves interest |
| HSBC | Divide by 2 | True fortnightly — saves interest |
| CBA | Multiply by 12, divide by 26 | Equivalent — no saving |
| NAB | Multiply by 12, divide by 26 | Equivalent — no saving |
| ANZ | Multiply by 12, divide by 26 | Equivalent — no saving |
| ING | Multiply by 12, divide by 26 | Equivalent — no saving |
| ubank | Multiply by 12, divide by 26 | Equivalent — no saving |
| Suncorp | Multiply by 12, divide by 26 | Equivalent — no saving |
| Bendigo and Adelaide | Multiply by 12, divide by 26 | Equivalent — no saving |
| Macquarie | Monthly only on direct debit | N/A — offset workaround available |
Westpac states the divide-by-2 method explicitly in its mortgage calculator assumptions: "if your monthly repayments are $1,000, fortnightly repayments are calculated by dividing $1,000 by 2 ($1,000 ÷ 2 = $500)." ubank's repayment calculator page is equally explicit about the opposite method: "we convert the monthly amount by multiplying it by 12 and then dividing it by 26 for a fortnightly figure." The other lenders fall on one side or the other but rarely advertise it.
Sally Tindall of RateCity put it neatly: "Westpac, Bank of Queensland and other lenders have purposely kept the formula this way to help their customers get ahead — something these banks should be congratulated for." (PropertyUpdate)
Macquarie is a special case. Its direct debit is monthly only and the frequency cannot be changed (Macquarie repayment frequency). The workaround Macquarie itself recommends is to credit salary into your offset account more frequently — variable loans only, not fixed. Because interest accrues daily on the loan balance net of offset, paying salary into a Macquarie offset fortnightly delivers a similar effect to true fortnightly elsewhere, without changing the direct debit at all.
The simpler alternative that works at any bank
The maths underneath all of this is straightforward:
True fortnightly = monthly ÷ 2 × 26 = monthly × 13 Monthly + 1/12 extra = (monthly + monthly/12) × 12 = monthly × 13
Those are the same number. Paying monthly and adding one-twelfth of your monthly repayment as an extra payment each month produces an identical saving to true fortnightly. No need to switch frequencies. No need to change banks. No need to argue with your lender about which method they use.
On the $500,000 example above, adding $240.78 per month to the $2,889.34 monthly repayment — total $3,130.12 per month — produces the same 24-year-10-month payoff and the same $109,000 interest saving as true fortnightly at Westpac.
For most Australians, this is the cleanest answer. It works at any lender, it survives a refinance, and it's easier to explain to your future self.
Why pay cycle alignment still matters
There's a separate reason fortnightly is popular in Australia: most workers are paid fortnightly. Aligning your largest single bill — the mortgage — with your pay cycle removes a chunk of cashflow stress. Money comes in, money goes out, the gap doesn't have to stretch across an awkward five-week period.
Even at lenders that use the equivalent method (CBA, NAB, ANZ, ING, ubank, Suncorp, Bendigo), switching to fortnightly for cashflow alignment is a perfectly reasonable thing to do. You just need to understand you're getting a cashflow benefit, not an interest saving. ANZ is unusually honest about this in its ANZ Plus repayment FAQ: the page frames fortnightly entirely as a cashflow management feature, not an interest-saving one.
If you want both — cashflow alignment and the interest saving — there are two ways:
- Stay monthly and add one-twelfth extra each month. Set up an automatic transfer of the extra straight after payday. Simpler at most lenders.
- Switch to a lender that uses true fortnightly if you're refinancing anyway. The interest saving is large enough on its own to be a tie-breaker.
A note on daily compounding
Australian home loans almost universally accrue interest daily and charge it monthly. That mechanic means more frequent payments do, technically, reduce interest by a tiny margin even at the equivalent method — because the principal is slightly lower for a few days each month. On a $500,000 loan, the saving from this effect alone is typically under $200 per year — real, but not what's worth getting excited about. RateCity's own modelling of a $500,000 loan with 25 years remaining put the equivalent-fortnightly saving versus monthly at $8,143 over 25 years (about $326 per year), with true fortnightly at the same lender saving $97,583 (PropertyUpdate / RateCity).
So the order of magnitude is clear: the big saving is from the extra payment, not from the compounding. Don't let a salesperson sell you the compounding line as the headline.
What about fixed-rate loans?
Most fixed-rate loans in Australia cap extra repayments — typically $10,000 to $30,000 over the entire fixed term, depending on lender. NAB allows $20,000 total during a fixed period (NAB fixed loan FAQ); Westpac caps at $30,000 total (Westpac). True fortnightly on a fixed loan — paying 13 monthly equivalents per year — adds one whole monthly repayment of "extra" each year, which can breach those caps over a multi-year fixed term and trigger break costs.
If you're fixed, the safer path is to stay monthly and either use the cap in lump sums close to the limit or split the loan — fix half for budget certainty and keep half variable for flexibility, with the variable portion on true fortnightly or monthly-plus-extra.
A short checklist before you change anything
- Find out which method your bank uses. Ask in writing, or look up the assumptions page on your bank's mortgage calculator. The wording you're looking for is either "divide by 2" (good) or "multiply by 12, divide by 26" (no saving).
- If your bank uses the equivalent method, either set up monthly-plus-extra at one-twelfth, or refinance to a true-fortnightly lender if the rate is competitive.
- Check fixed-rate caps before increasing payment frequency if you're on a fixed loan.
- Don't switch to weekly thinking it's much better than fortnightly. It isn't — the extra saving is real but small.
- Run the numbers in the Calcula mortgage calculator with your own loan size, rate and term. Side-by-side, the difference between true fortnightly, equivalent fortnightly and monthly is much easier to see than read about.
A short reminder on advice
This article describes how Australian lenders generally handle repayment frequency in 2026 and the maths of the resulting interest saving. It is not personal financial or credit advice. Lender methods can change without warning and your individual loan terms — especially on fixed-rate products — can affect whether more frequent or larger repayments suit your situation. Speak to a licensed mortgage broker before making a structural change to your loan.
For the source pages on each major lender's method, see Westpac's mortgage calculator assumptions and ubank's repayment calculator assumptions for the two opposite ends of the spectrum.