Common CAGR Mistakes (and a Better Way)

Updated 15 August 2026 · Savings and investing

A CAGR 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 CAGR calculations in Australia, and how to avoid them.

1. Comparing total rather than annual returns

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

2. Chasing bonus rates without meeting conditions

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

3. Forgetting tax on returns

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

4. Ignoring inflation

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

5. Overlooking the detail that matters most here

CAGR smooths out ups and downs. Two investments with the same CAGR can have very different risk.

How the compound annual growth rate changes with ending value

A common mistake is getting one input slightly wrong. Here is what happens to the compound annual growth rate when “Ending value ($)” is off by up to 20% in either direction, with everything else held steady.

Ending value ($)	Compound annual growth rate
64,000	5.06%
72,000	7.57%
80,000	9.86%
88,000	11.97%
96,000	13.94%

At 64,000 the result is 5.06%; at 96,000 it is 13.94%. 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

CAGR = (end ÷ start)^(1 ÷ years) − 1. With typical inputs the calculator returns compound annual growth rate of 9.86%. 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.