See what a steady return and regular deposits add up to, next to the same plan with half the return. It is arithmetic, not a forecast.
Balance after each period = previous balance × (1 + return) + contribution
Compounding is real, but the inputs are the whole story. A return of 2% per month needs to be earned every month without a bad one, which almost nobody does. The half-return line is there to show how sensitive the end result is to that single assumption. Contributions alone are shown so you can see how much of the final balance is your own money.
A bad stretch changes the picture: after a loss you need a larger gain to recover, so a plan with steady returns overstates what a plan with swings produces. The drawdown calculator shows that gap.
Questions people ask
How is compound growth calculated?
Each period the return applies to the whole balance, including earlier growth. Then any new contribution is added before the next period.
Is a steady monthly return realistic in trading?
Rarely. Results swing, and large losses are harder to recover from than the same gain is to make. Compare the plan with the half-return line.
What return should I enter?
Use a conservative figure you could defend, not the best month you remember. The calculator is most useful for seeing how much the answer depends on it.