Knowing how savings account interest actually works helps you make smarter decisions about where to keep your money. This guide covers the mechanics of interest calculation in Australia, from daily accrual to compounding.
How Banks Calculate Interest
Australian banks calculate interest on savings accounts on a daily basis using your end-of-day balance. The formula is straightforward:
Daily interest = (Annual rate / 365) x Account balance
On a $50,000 balance earning 5.00% p.a.:
- Daily interest = (0.05 / 365) x $50,000 = $6.85 per day
- Monthly total = roughly $205 (for a 30-day month)
- Annual total = $2,500
Interest is typically credited monthly, usually on the last business day. This is when the earned interest gets added to your balance and starts earning interest itself - that's compounding.
Annual Percentage Rate (p.a.) Explained
When a bank advertises a rate like 5.00% p.a., the "p.a." means per annum (per year). This is the standard way Australian banks express rates, regulated by ASIC.
Because interest is calculated daily and credited monthly, the effective annual rate is slightly higher than the advertised rate due to compounding:
| Advertised Rate | Effective Rate (monthly compounding) |
|---|---|
| 4.00% p.a. | 4.07% |
| 4.50% p.a. | 4.59% |
| 5.00% p.a. | 5.12% |
| 5.50% p.a. | 5.64% |
The difference is small but real, especially on larger balances over longer periods.
How Bonus Interest Works
Most high-rate savings accounts in Australia split their interest into a base rate and a bonus rate. This split determines what you actually earn.
Take UBank's Save Account as an example:
- Total rate: up to 5.35% p.a. (new customers, first 4 months) / 4.60% p.a. (ongoing)
- Base rate: 0.00% (applied when conditions are not met)
- Bonus conditions: Grow balance by $1/month
If you meet the condition, interest is calculated at your applicable bonus rate for every day of that month. Miss it, and you earn 0.00% for the entire month.
The calculation happens retrospectively at month-end. The bank checks whether you met the conditions, then applies either the full rate or just the base rate to every day of that month.
Balance Tiers and Caps
Many banks apply different rates depending on your balance. This is called tiered interest or stepped rates.
ING Savings Accelerator Tiers
ING's Savings Accelerator uses a tiered structure where the rate applies to your whole balance (not just the portion in each tier):
- Balances up to $500,000 earn the top rate of 5.40% p.a. (new customers, first 4 months)
- Above $500,000, a lower rate applies
Stepped vs Whole-Balance Rates
There are two types of tiered rates:
- Whole-balance: The rate applies to your entire balance (ING model). If you exceed the cap, a different rate applies to everything.
- Stepped: Different rates apply to different portions of your balance simultaneously. For instance, 5.00% on the first $50,000, then 2.00% on the next $50,000.
Always check which model your bank uses - it significantly affects what you earn on larger balances.
Interest Credit Timing Matters
When your interest is credited (added to your balance) affects compounding:
- Monthly crediting (most common): Interest earned in January is added to your balance on ~31 January, then earns interest itself from February
- Quarterly crediting: Less common for savings accounts, means you compound less frequently
For a $100,000 balance at 5.00% p.a., the compounding benefit of monthly vs quarterly crediting is roughly $12-15 per year. Small, but free money.
Tax on Savings Interest
Interest earned on savings accounts is taxable income in Australia. Your bank will report interest payments to the ATO automatically.
Key points:
- Provide your Tax File Number (TFN) to your bank, otherwise they'll withhold tax at the highest marginal rate (currently 47%)
- Interest appears on your pre-filled tax return
- The tax you pay depends on your total annual income and marginal tax rate
For someone earning $80,000 per year (30% marginal rate + 2% Medicare levy), earning $2,500 in savings interest would result in roughly $750 in tax.
How to Maximise Your Interest
- Keep funds in the highest-rate account for as many days as possible - interest is calculated daily
- Avoid withdrawals mid-month if your account has a no-withdrawal bonus condition
- Time large deposits for early in the month to maximise the number of days earning interest
- Compare effective rates on our savings comparison page, which shows the actual rate you'd earn after accounting for conditions and caps
Related Guides
- Best Savings Accounts in Australia for 2026 - our full comparison
- Bonus Savings Accounts Explained - understanding conditions
- Rate News - daily tracking of rate changes across the market
Frequently Asked Questions
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