The short, honest answer: it's savings. The money never goes into the loan, never becomes "capital," and stays fully yours to spend. What it does is change the number your interest is calculated on - and that turns out to be surprisingly powerful.
Each period, your lender charges interest on (loan balance − offset balance) instead of the full loan balance. That's the entire mechanism. Your loan balance doesn't change any faster because money sits in offset - what changes is that less of your unchanged repayment goes to interest, so more of it reduces the principal. The repayment does the paying-off; the offset just stops interest eating it.
The Reserve Bank of Australia describes it precisely: money in an offset account effectively earns your mortgage interest rate, because that's the rate of interest you stop paying - and unlike a savings account, that benefit isn't taxable income, because saving interest isn't earning interest. Six percent, tax-free, on money you can still access - a savings account would need to pay well above 8% before tax to match it for most taxpayers. That framing comes from the RBA's own research on the Australian mortgage market, not from a bank's marketing page.
| Money in offset | Extra repayment | |
|---|---|---|
| Interest effect | Identical - interest charged on net balance | Identical - interest charged on lower balance |
| Access | Fully accessible, like any account | Depends on redraw - lender-controlled, can be restricted |
| Loan balance | Unchanged | Actually reduced |
| Discipline | Easy to spend - it's right there | Psychologically "locked away" |
Mathematically, a dollar in offset and a dollar of extra repayment save identical interest. The difference is everything else: offset money stays yours unconditionally, while redraw access to extra repayments sits at the lender's discretion. The honest trade: offset buys flexibility, extra repayments buy commitment. Try both in the loan calculator - it models offset balances, monthly offset contributions, and extra repayments side by side, month by month.
Offset accounts usually come packaged with annual fees or a slightly higher rate - commonly a few hundred dollars a year. The benefit only outruns the cost if your average balance is high enough: at 6%, a $400/year package fee needs about $6,700 sitting in offset year-round just to break even. A small or occasional balance can genuinely make an offset package worse than a basic loan. Average balance is what matters, not the peak after payday.
Offset accounts are mainstream in Australia - used on roughly 40% of mortgages, with balances the RBA measured in the tens of billions - real but less common in the UK and New Zealand, and generally not offered in the United States. If you're comparing tools or advice written for the US market, this is why offset never comes up.