A steady savings plan can produce dramatic results. If you put aside $100 a month starting at age 20 and keep at it, you'll accumulate more than $114,000 by the time you're 65. That assumes a 3 percent interest rate. If you sock away $250 a month and rates go up to 5 percent, you'll end up with more than $500,000. Plug your own numbers into the calculator below.