Getting the Most From a Term Deposit Calculator: Tips and Common Errors

Updated 9 August 2026 · Savings and investing

A Term Deposit Calculator gives a fast answer, but the answer is only as good as what goes in. These are the mistakes we see most often with term deposit calculations in Australia, and how to avoid them.

1. Forgetting tax on returns

Interest is taxed at your marginal rate, so a 5% account may return closer to 3.4% after tax.

2. Ignoring inflation

A return below inflation means your money buys less over time.

3. Comparing total rather than annual returns

Always convert returns to a yearly rate before comparing investments held for different periods.

4. Chasing bonus rates without meeting conditions

Missing a deposit or making a withdrawal can drop a bonus saver to its low base rate.

5. Overlooking the detail that matters most here

Many term deposits roll over automatically at a lower rate. Set a reminder before maturity.

How the interest at maturity changes with interest rate

A common mistake is getting one input slightly wrong. Here is what happens to the interest at maturity when “Interest rate (%)” is off by up to 20% in either direction, with everything else held steady.

Interest rate (%)	Interest at maturity
3.6	$720.00
4.05	$810.00
4.5	$900.00
4.95	$990.00
5.4	$1,080.00

At 3.6 the result is $720.00; at 5.4 it is $1,080.00. If a small change in this input moves the answer a lot, it is worth double-checking that figure before you rely on the result.

A quick sense check

Interest = amount × rate × months ÷ 12. With typical inputs the calculator returns interest at maturity of $900.00. If your own result looks wildly different, check that each figure is in the right unit and period (weekly, monthly or yearly) before drawing conclusions.