How your investments perform is a big factor in whether you'll have enough money to retire. But the biggest factor is how much you actively save.

As Money Magazine's Penelope Wang points out, suppose you started work in 1990 with a $40,000 salary. You saved just 2 percent of your pay and invested in the top-returning funds every year. You would have finished 2005 with nearly $50,000.

By contrast, if you picked mediocre funds every year but were frugal enough to save a full 6 percent of your salary, you'd end up with nearly $120,000.

There's another reason to contribute more than a paltry 2 percent. You want to contribute enough to get the full match offered by your employer. If you have no problem turning down free money, you might want spend a few bucks to ask a therapist why.

Remedy:

Fidelity has a calculator that will show how your contributions will affect your take-home pay.

If you can't afford to max out your contributions, at least contribute enough to get the full match from your employer. (So if the boss offers to kick in 50 cents on the dollar up to 6 percent of your pay, contribute at least 6 percent of your pay.) Then boost your annual contributions by one to two percentage points every year. A little goes a long way.