What the calculation measures
Compounding means each period's growth is applied to prior growth as well as contributed principal.
How to interpret the result
Run multiple return scenarios instead of assuming a single long-term rate will occur every year.
Run scenarios instead of one answer
Change the most uncertain input and compare outcomes. A calculator is most useful when it shows sensitivity, not when one estimate is treated as a guarantee.
Limits and assumptions
Investment returns are uncertain and taxes, fees and contribution timing can change actual outcomes.