Time is an ingredient, too.
How compounding turns time into part of the equation.
Growth on top of growth
Compounding means that returns can earn returns of their own. If an investment grows, the next period starts from a larger base. The same mechanism also works against you when losses reduce that base. A steady assumed rate makes the maths easy to model, but real markets never move in a straight line.
Contributions change the picture
Adding money regularly increases the capital exposed to future returns. The timing matters: a contribution at the end of a month has one less month to grow than a contribution at the beginning. Marketwise uses end-of-month contributions and converts the annual assumption into its equivalent monthly rate.
A scenario is not a promise
Try several rates, including zero and negative returns. Consider fees, taxes, inflation, and your need to access the money. A useful model helps you ask better questions; it does not tell you what will happen.