Common Age Mistakes (and a Better Way)

Updated 16 September 2026 · Everyday

A Age 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 age calculations in Australia, and how to avoid them.

1. Ignoring supply charges

Electricity bills include a daily supply charge on top of usage.

2. Forgetting public holidays

Day counts don’t know about state public holidays, so allow for them in deadlines.

3. Using the wrong units

Australia uses litres per 100 km for fuel and cents per kWh for electricity. Converting from other units introduces errors.

4. Stacking percentages

Percentage changes compound, so they can’t simply be added or subtracted.

5. Overlooking the detail that matters most here

Use the second date to check age on a future date, such as eligibility for a licence or pension.

A quick sense check

Age = the difference between two dates, borrowing days and months where needed. With typical inputs the calculator returns age of 36 years, 8 months, 13 days. 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.