What is "dollar cost averaging"? How does it work?

Dollar cost averaging is a method of accumulating assets by purchasing a fixed dollar amount of securities, in regularly scheduled intervals, over a period of time (e.g., $100 per month over the next five years). When the price of the securities is high, your fixed dollar amount will buy fewer securities, but when the price of the securities is low, your fixed dollar amount will buy more. For example, when your share price is $25 you will purchase four shares, but when the price drops to $20 you will buy five shares. This allows you to take advantage of the fluctuations in the market. Historically, the markets have always gone up over the long term. As a result, dollar cost averaging with a fixed dollar amount should yield a lower average per share price than if you bought a fixed number of securities for each periodic interval.
Note: 401(k) contributions are a good example of dollar cost averaging, because they are deducted from each of your paychecks and then sent to the investment company.
Dollar cost averaging is often favored by those who wish to make their periodic investment a part of their monthly budget. The amount invested each month is predictable. An automatic investment plan (e.g., a systematic electronic draft from your checking account) will ensure that the predetermined amount is properly invested at appropriate intervals. Among other things, this relieves you of the concern and emotional burden that comes with trying to decide when, and how much, you should be investing when the price of your securities is rising or falling. Experts suggest that this strategy works best with a single investment vehicle that regularly fluctuates in price, such as a growth mutual fund.