Dollar Cost Averaging - Still a Good Idea?

When you dollar cost average (DCA), you invest a certain sum of money in a specific investment (or investments) on a pre-set schedule. For example, you might arrange to put $100 into mutual fund X on the first day of every month. The primary advantage of dollar cost averaging is that you will buy more shares when the price of the investment is low and fewer shares when it is comparably higher. You automatically use DCA when you sign up for your 401(k) plan.

So, when wouldn't DCA be a good idea?

Turns out, about two-thirds of the time. Since the stock market generally goes up (notwithstanding the nearly two years of current market pain), by waiting to invest a lump sum of money, you miss out on more of the long-term price appreciation. Still, if and when you have a lump sum to invest, you don't know if we're about to enter a period of time when you would be better off investing all at once (two-thirds of such situations) or doing so over several months or longer (one-third of similar occasions). Like everything else, using dollar cost averaging is a trade-off between risk and reward. What would you do? What do you actually do? What do you think about dollar cost averaging?

By Michael Rubin, About.com Guide to Retirement Planning