The absolute best way to save for retirement is to start young. If you start saving $100 per month when you're 25, and you invest that in a mutual fund or other stock-related fund that sometimes earns 18-percent interest and sometimes loses money, averaging 8 percent over the next 40 years, you'll have $351,428.13 for retirement.

To get the same amount of retirement savings if you start at age 40, you'll have to put away about $367 per month. Use FinAid's Savings Growth Projector Calculator to run these numbers for yourself.