What is a high-interest savings account?
A high-interest savings account (HISA) is a deposit account that pays a competitive interest rate on your balance. In Australia, most HISAs are offered by banks and credit unions and are protected by the government's Financial Claims Scheme up to $250,000 per account holder per institution.
Interest is typically calculated daily and paid monthly. Many accounts require conditions to be met to earn the advertised "bonus" rate, such as making a minimum number of deposits per month, not making any withdrawals, or maintaining a minimum balance. The base rate without the bonus is usually significantly lower.
The critical point for tax: interest earned in a HISA is ordinary income. It is added to your taxable income in the year it is received and taxed at your marginal rate.
What is a mortgage offset account?
A mortgage offset account is a transaction account linked directly to your home loan. Each day, your lender calculates mortgage interest on the difference between your loan balance and your offset account balance, not on the full loan.
If you have a $500,000 loan and $60,000 sitting in your offset account, interest is charged on $440,000 rather than $500,000. The loan repayment amount typically stays the same, but because less of each payment covers interest, more goes toward reducing the principal, which shortens the loan term.
An offset account functions like an ordinary transaction account. You can have your salary deposited into it, pay bills from it, and access funds at any time. The offset effect applies to whatever balance is in the account each day.
How the interest saving works, a concrete example
Consider a $500,000 mortgage at 6.20% interest, with $50,000 available to park somewhere.
- In an offset account: interest is charged on $450,000 instead of $500,000. Annual interest saving: $50,000 × 6.20% = $3,100. This saving is not taxable income.
- In a HISA at 5.20%: annual interest earned = $2,600. At a 37% marginal rate, tax takes $962, leaving $1,638 after tax.
- Difference: the offset delivers $3,100 in effective benefit vs $1,638 from the HISA, nearly double, purely from the tax treatment.
The effective return on money in an offset account is identical to your mortgage interest rate, completely tax-free. No savings account can match this unless it pays a rate higher than your mortgage rate, which is extremely rare.
Tax treatment: the decisive difference
The fundamental advantage of an offset account over a savings account is tax. The benefit you receive from an offset is not classified as income, it is simply interest that was never charged. You pay no tax on it, ever.
Interest earned in a HISA is added to your taxable income and taxed at your marginal rate. At a 37% rate, only 63 cents of every dollar of HISA interest reaches you; at 45%, only 55 cents does.
This means the higher your income, the larger the advantage of an offset. For someone on the 45% marginal rate, a HISA would need to pay roughly 11.27% to match a 6.2% offset account. For the 30% rate, the break-even is around 8.86%. Neither figure is achievable with current deposit rates, so the offset wins for most mortgage holders at most income levels.
When a HISA makes more sense
There are situations where a HISA is the right choice:
- You do not have a mortgage: an offset account only makes sense if there is a loan to offset it against. If you are saving for a deposit, building an emergency fund, or have paid off your home, a HISA is the natural choice.
- Your mortgage is small relative to your savings: once the offset balance equals the loan balance, the interest reduction is capped (you cannot reduce interest below zero). Extra funds above the loan balance earn nothing in the offset and belong in a HISA or investments.
- Your loan does not offer an offset: fixed-rate loans and some basic variable products do not include an offset. In this case, a HISA is the next best option for accessible savings.
- Your tax rate is very low: at the 0% or 15% rate (income below $18,200 or in super accumulation phase), the tax drag on HISA interest is minimal and the offset advantage shrinks.
Emergency funds: which account?
An emergency fund should be liquid, accessible within a day without penalty. Both a HISA and an offset account satisfy this requirement.
If you have a mortgage, keeping your emergency fund in an offset account is almost always the better choice. The money remains fully accessible (it is just a transaction account), and every dollar earns the same effective return as the mortgage rate, tax-free. There is no lock-up and no conditions to satisfy.
If you do not yet have a mortgage (for example, you are still renting while building your emergency fund), a high-interest savings account is appropriate. Look for a HISA with no minimum withdrawal amount, no notice period, and a competitive rate without onerous bonus conditions.
The standard recommendation is 3–6 months of essential expenses. Use the Emergency Fund Calculator to calculate the right target for your situation.
Mortgage optimisation with an offset
Mortgage interest in Australia is calculated daily. This means the balance in your offset account on any given day directly reduces that day's interest accrual. Keeping as much cash as possible in the offset for as many days as possible minimises total interest paid.
Receive your salary into the offset
Having your salary paid directly into your offset account means your full take-home pay reduces the effective loan balance from the day it arrives. Even if you spend it over the following weeks, the daily average balance in the offset is higher than if you transferred money in only occasionally.
Pay expenses at end of the month
Some mortgage holders pay regular bills by credit card and settle the card at the end of the statement period rather than immediately. This keeps more cash in the offset for longer, reducing daily interest. This only works effectively if the credit card has no annual fee and is paid in full each month, carrying a balance on a credit card at 20%+ interest eliminates any offset benefit many times over.
Offset vs redraw
An offset account and a redraw facility both reduce the interest you pay, but they work differently and have different tax implications if the property ever becomes an investment. For a detailed comparison, see the Mortgage Offset vs Redraw guide.
Pros and cons at a glance
High-interest savings account
- Pro: Works for anyone, with or without a mortgage
- Pro: Easy to open, widely available
- Con: Interest is taxable income at your marginal rate
- Con: Bonus rate conditions can be restrictive or difficult to maintain
- Con: Rate is usually lower than a mortgage rate, so the after-tax return is substantially lower than what an offset would save
Mortgage offset account
- Pro: Benefit is equivalent to the mortgage rate, tax-free, typically the highest after-tax return available for liquid cash
- Pro: No conditions, the benefit applies to every dollar, every day
- Pro: Shortens loan term and reduces total interest paid over the life of the loan
- Con: Requires a mortgage, not useful without a loan to offset
- Con: Not available on all loan types, less common on fixed-rate loans
- Con: Some lenders charge a higher rate or annual fee for offset-enabled loans
Common mistakes
Keeping savings in a HISA while carrying a mortgage
This is the most common and costly mistake. Even the best HISA rate, after tax at a typical marginal rate, falls well short of the tax-free return that the same funds would generate sitting in a mortgage offset. If you have a mortgage and accessible savings, the offset almost always wins.
Leaving savings in redraw instead of offset
Both reduce your effective loan balance and save interest, but redraw funds are legally part of the loan, the lender can restrict access in certain circumstances. Offset funds are in a separate deposit account and are always accessible. See the Offset vs Redraw guide for the full comparison, including the tax implications for future investment property owners.
Letting the offset balance creep down through discretionary spending
An offset account doubles as your everyday transaction account, which means discretionary spending directly erodes the balance and the interest saving. Spending $10,000 on a holiday from your offset costs you the interest saving on $10,000 for the remainder of the loan, not just the cash itself. Being deliberate about maintaining the offset balance matters.
Ignoring the loan product comparison
Some lenders charge more for a loan with an offset feature than for a basic variable loan without one. If the additional cost of the offset loan exceeds the interest saving the offset would generate, the feature is not worthwhile. Run the numbers based on your likely offset balance and mortgage rate before choosing a product.
Frequently asked questions
Can I have both a high-interest savings account and an offset account?
Yes. Many Australians hold both: the offset account linked to their mortgage maximises interest savings on the home loan, while a separate HISA might hold funds earmarked for a goal without a mortgage (a car, holiday, or future deposit). The key is to put the bulk of your available cash in the offset first if you have a mortgage, since that return is almost always superior after tax.
Is the money in my offset account protected by the government guarantee?
Yes. The Financial Claims Scheme protects deposits of up to $250,000 per account holder per authorised deposit-taking institution (ADI). An offset account is a deposit account at a bank or credit union, so it qualifies. If your offset balance exceeds $250,000 at one institution, the excess is not guaranteed.
Does every mortgage come with an offset account?
No. Offset accounts are a feature that varies by lender and loan product. They are most common on variable-rate home loans and some split loans. Basic variable or fixed-rate loans often do not include an offset. Lenders that do offer offset accounts sometimes charge a higher annual fee or a slightly higher interest rate for that feature, factor this into your comparison.
Can I use an offset account if I have a fixed rate mortgage?
Fixed rate loans generally do not offer a true offset account. Some lenders offer a partial offset on fixed loans, but the mechanics differ. The main use case for an offset account is a variable rate loan where interest is calculated daily on the reduced balance.
Is the benefit I get from an offset account taxable?
No. The interest you save by having funds in an offset account is not income, it is simply interest that was never charged. You do not report it anywhere on your tax return. This is the key tax advantage of the offset over a savings account, where the interest earned must be declared as taxable income.
What is the break-even HISA rate that beats an offset?
The break-even point depends on your marginal tax rate and mortgage interest rate. For an offset at 6.2% with a 37% marginal rate, a HISA would need to pay more than 9.84% (6.2% ÷ 0.63) to be equivalent after tax. For a 30% rate, the break-even is about 8.86%. These thresholds are well above current savings account rates, so for most Australian mortgage holders the offset wins on every dollar.
Calculate your emergency fund target
Whether your emergency fund goes into an offset or a HISA, the Emergency Fund Calculator can help you work out the right target based on your expenses and employment type. Use the Mortgage Repayment Calculator to model how extra funds in an offset shorten your loan term.