How the projection works
Your current savings grow on their own, while each monthly contribution is added and then compounds for the years that remain. The calculator models contributions as an ordinary annuity, compounding monthly, and separates your final balance into the money you put in and the growth it earned.
Time is the biggest lever
The earlier you start, the larger the share of your retirement balance that comes from growth rather than contributions. Starting in your twenties with modest amounts often beats starting later with much larger ones, because those early dollars compound the longest.