You've heard it all before: Save for your retirement! Start saving early! But do you really appreciate how vital it is to start saving and investing as soon as possible? And if you're already saving and investing, do you appreciate how much more important this year's dollars are than the dollars you might invest a few years from now?

Let's see how a $3,000 investment will grow over time at the market's historic average annual rate of 10%. (That average, of course, could move higher or lower over time.)

  • Year 1: $3,000
  • Year 2: $3,300
  • Year 10: $7,074
  • Year 15: $11,392
  • Year 20: $18,348
  • Year 25: $29,549
  • Year 30: $47,589

Now, here are some things to note:

  • Obviously, the pile of greenbacks is growing more rapidly in the later years. But think about what that means. Between year 29 and year 30, the pile grew from $43,263 to $47,589 -- a difference of $4,326. If you'd invested that initial $3,000 just one year later, you'd have missed out on that last year of growth.
  • Did you notice that the $4,326 you'd earn in that last year is considerably more than your entire initial investment? Wow.
  • Change the numbers to suit your portfolio. If you have a nest egg worth $30,000 now, you would miss out on some $43,263 by missing that last year. If you're worth $300,000, you'd miss out on $432,630 -- not far from half a million bucks.
  • Realize that even if you invested $50,000 in year 29, if it grew by 10%, it would generate $5,000 -- not much more than your initial $3,000 would generate. That early money simply had more time to do its stuff.

Understand that you might earn even more than 10%, on average, per year, if you invest in some carefully selected successful stocks or mutual funds. The Muhlenkamp Fund (FUND:MUHLX), for example, has averaged about 13% annual growth over the past five and 10 years. Its top holdings recently included Altria (NYSE:MO), Cemex (NYSE:CX), Caterpillar (NYSE:CAT), Nabors Industries (NYSE:NBR), and Whirlpool (NYSE:WHR).

What to do
So get yourself in gear. It really is important to start investing, and to do so in earnest beginning in your early years.

We'd love to help you plan and save effectively for your future with our Rule Your Retirement newsletter. A free trial will give you full access to all past issues, where you can gather up valuable tips and even read how some folks have retired early and well. The service regularly highlights promising stocks and mutual funds, too.

And keep some money out of stocks!
Before you start socking money away for the distant future, though, make sure you've got some short-term savings in order. Learn why you need an emergency fund and how to best invest that money by visiting our Savings Center. For starters, know that your short-term money should not be in stocks, because over short periods -- even several years -- anything can happen in the stock market. You don't want your emergency money to be cut in half just because of bad timing.

Longtime Fool contributor Selena Maranjian owns shares of Cemex, which is a Stock Advisor and Global Gains recommendation. Try any one of our investing services free for 30 days. The Motley Fool isFools writing for Fools.