Almost every question about home loans — why offset works, whether paying early helps, why two months differ — comes back to a single mechanic that lenders rarely explain clearly.
Interest accrues daily. It is charged monthly.
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The daily calculation
Each day, your lender takes your closing balance and multiplies it by your annual interest rate divided by the number of days in the year. That day’s interest is recorded but not yet charged. At the end of the month, the daily amounts are added together and debited.
On a $600,000 balance at 6.5%, one day of interest is about $106.85. Nothing is charged that day — it accumulates quietly until the monthly debit.
Why this explains offset accounts
Because the calculation runs on your daily balance, an offset account reduces the figure being multiplied every single day it holds money.
Hold $50,000 in offset against that same loan and the daily interest falls from about $106.85 to about $97.95 — roughly $8.90 a day, or about $3,250 over a year. That is simply 6.5% of $50,000, which is the point: an offset balance earns your loan rate rather than a savings rate.
It also explains why having your salary paid into the offset account helps even if you spend it before month end. Every day it sits there is a day of reduced interest.
Why your months differ
A 31-day month accrues more interest than a 28-day month at the same balance and rate, because there are more days to multiply. Borrowers occasionally query a February statement that looks unusually low. Nothing is wrong.
Lenders also differ in whether they divide the annual rate by 365 or 366 in a leap year, which produces small variations between institutions on otherwise identical loans.
This daily-accrual, monthly-charge structure is why a calculator can only ever approximate your statement. The model assumes clean periods; your lender counts actual days.
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Does paying a few days early help?
Slightly, and less than people hope. Paying five days before the due date means five days at a marginally lower balance, which on a typical loan amounts to a few dollars.
The effect is real but small. It is not a strategy — the amount you repay matters vastly more than the day you repay it. Where timing does matter is the offset account, because that balance can be large and can sit there continuously.
Why the first repayment is often unusual
Your first repayment frequently differs from every one after it. If your loan settles mid-month, the first period may cover more or fewer days than a standard month, so the interest component is calculated over that odd stretch.
Some lenders charge an interest-only amount for the partial first period, then begin normal principal and interest repayments. Your amortisation schedule may therefore be a period longer than the arithmetic suggests.
Key takeaways
- —Interest accrues daily on your balance and is charged monthly.
- —One day on $600,000 at 6.5% is roughly $107.
- —Offset works because it reduces the daily balance being multiplied.
- —Longer months cost more interest than shorter ones at the same balance.
General information only. This guide explains how these products generally work. It does not take account of your objectives, financial situation or needs, and is not financial product advice under the Corporations Act 2001 (Cth). Figures are illustrative. Speak to a licensed financial adviser before acting.