Fortnightly repayments only shorten your loan if you pay exactly half your monthly repayment every fortnight. Because there are 26 fortnights but only 12 months in a year, that produces the equivalent of 13 monthly payments instead of 12. If your lender instead divides your annual repayment into 26 equal instalments, you pay the same amount each year and the benefit is negligible.
This is the most repeated piece of mortgage advice in Australia, and it is usually explained wrongly. The benefit is real but it is not magic, and whether you get it depends entirely on how your lender configures the arrangement.
Where the benefit really comes from
A year contains 12 months. It also contains 26 fortnights, which is 13 lots of two fortnights — not 12.
So if you take your monthly repayment, halve it, and pay that half every fortnight, over a year you pay 26 half-payments, which equals 13 monthly payments. You have made one extra monthly repayment without deciding to.
That extra payment is the entire benefit. It is not that paying more often reduces interest in some structural way — interest is calculated daily on the outstanding balance, so paying a fortnight earlier helps marginally, but the effect is small. The thirteenth payment is what shortens the loan, and it does so meaningfully because it goes almost entirely to principal.
The two arrangements, and why the difference is everything
| Arrangement | What you pay a year | Effect |
|---|---|---|
| Half the monthly amount, every fortnight | 13 monthly equivalents | Genuine, worth having |
| Annual repayment divided by 26 | 12 monthly equivalents | Almost nothing |
Both are called fortnightly repayments. Only the first does anything.
Some lenders default to the second, because it keeps your annual outgoing identical and is therefore an easier conversation. If you asked for fortnightly repayments expecting to pay your loan off years early and your annual total did not change, this is why.
Ask your lender one question: “Is my fortnightly repayment exactly half of what my monthly repayment would be?” If the answer is no, you are on the arrangement that does nothing, and you can usually ask to change it.
Weekly repayments
The same logic extends. There are 52 weeks in a year, so paying a quarter of the monthly repayment each week gives you the equivalent of 13 monthly payments again. Weekly is not better than fortnightly done properly — it produces the same thirteenth payment, just in smaller slices.
The real argument for weekly is behavioural. If you are paid weekly, matching your repayment to your pay cycle makes budgeting easier and reduces the chance of a missed payment. That is a decent reason on its own.
When it will not work for you
- Fixed loans. Many restrict repayment frequency, and the extra amount may count towards a capped annual extra repayment allowance.
- Interest only loans. There is no principal being reduced, so the thirteenth payment has nothing to shorten. It simply sits in redraw or reduces the next charge.
- If your lender recalculates the minimum. Some reduce your required repayment once you are ahead, which quietly cancels the benefit. Check whether being ahead reduces future obligations.
- If the cash flow does not fit. Paying 13 months of mortgage in 12 means finding an extra month over the year. If that is a stretch, a smaller sustainable increase is better than a plan that fails in March.
The simpler alternative
If your lender will not configure fortnightly repayments usefully, you can get the identical result on a monthly schedule: increase your monthly repayment by one twelfth. Over the year you pay the same thirteen months’ worth.
This is often easier to arrange, easier to understand, and easier to reverse if money gets tight. It also avoids the ambiguity about which arrangement you are on, because you can see the higher number on your statement.
Whichever route you take, the fortnightly repayment calculator shows what the thirteenth payment does to your term and total interest. For most balances the result is years, not months — which is why the advice persists despite usually being explained badly.
Where it sits among the other levers
Worth keeping in proportion. Getting your interest rate right is generally a larger and more certain gain, and it costs nothing. Maintaining your repayment when rates fall is similarly free. Fortnightly repayments are a good habit, not the main event.
The full ranking is in how to pay off your home loan faster.
Common questions
Compare your fortnightly repayment to your monthly one. If the fortnightly figure is exactly half the monthly figure, you are on the useful arrangement. If it is roughly 46% of it, your annual repayment has simply been divided by 26.
Not financially, if both are set up as a proper fraction of the monthly repayment. Both produce the equivalent of thirteen monthly payments a year. Weekly can be better behaviourally if you are paid weekly.
Sometimes, but many fixed loans restrict frequency and cap extra repayments. Check whether the additional annual amount would breach your cap before changing.
No. It does not change your rate. It changes how much principal you repay in a year, which is what shortens the loan.
Financially they are equivalent if the amounts match. Fortnightly tends to work better in practice because it is automatic and spread out, rather than requiring you to find a lump sum.