It's simple. The earlier you begin investing, the more money you'll have for retirement. That's because you're giving your money more time to grow. On top of that, you have more time to ride out market downturns. With more time on your side, your retirement savings will have more time to rebound if the markets take a dive.

Consider the story of two twenty-five-year-olds, Madison and Cooper. Madison invests $2,000 annually over ten years, stashing the money away in her company's 401(k) plan. Then she stops at age thirty-five, never adding another penny into her plan. Madison can expect an average 10 percent annual growth rate on her investments. Because she started early and gave her money time to grow before taking it out at retirement, she can cash out at age sixty-five with $556,197.

Starting at age thirty-four, Cooper socks $2,000 away in his 401(k) plan every year for the next thirty years. Cooper ends up putting away three times as much money as Madison. But his retirement stash — which has earned the same rate of return over the years — is just $328,988. That's much less — more than $225,000 less — than Madison's.

Both Madison and Cooper had the power of compound interest on their side. Madison harnessed it earlier and thus reaped higher gains. Here's the moral of the story: If you can afford to live without those tens or even hundreds of thousands of dollars in retirement, then by all means procrastinate. The easiest way to figure out the compounding effect on the money you're putting away is with an online retirement calculator (try the one at www.finance.cch.com).