Dollar-cost averaging (DCA) means investing the same amount of money at regular intervals, for example $200 on the first of every month, no matter what the market is doing. If you contribute to a 401(k) from each paycheck, you are already doing it.
How it works in practice
Because the amount is fixed, you automatically buy more shares when prices are low and fewer when they are high. Example with $300 a month into one fund:
- Month 1: price $30 → 10 shares
- Month 2: price $20 → 15 shares
- Month 3: price $25 → 12 shares
You invested $900 and own 37 shares, an average cost of about $24.32, below the simple average price of $25. That small edge appears whenever prices move around, but it is not a guarantee of profit: if the investment keeps falling, you still lose money.
Does it reduce risk?
DCA reduces timing risk, the danger of putting everything in the day before a crash. It also reduces regret, which is a real benefit: people who invest regularly are less likely to freeze or panic. It does not reduce the risk of the investment itself. A bad fund bought gradually is still a bad fund.
Lump sum or DCA?
If you already have a large sum (an inheritance, a bonus), studies by firms such as Vanguard have found that investing it all at once has beaten spreading it out roughly two-thirds of the time, simply because markets rise more often than they fall. But a lump sum feels worse if a drop comes right after.
A reasonable middle path: if investing everything at once would keep you awake at night, spread it over a fixed period, for example 6 to 12 months, and stick to the schedule.
How to set it up
- Pick a diversified, low-cost fund (index funds work well).
- Choose an amount you can keep up through good and bad months.
- Automate it: payroll deductions for a 401(k), or automatic investments at your broker. Most brokers allow recurring purchases, including fractional shares.
- Turn on dividend reinvestment.
- Leave it alone. Check it occasionally, not daily (how often to check your investments).
Where DCA falls short
- It does not choose good investments for you.
- Frequent small purchases can cost money if your broker charges commissions (most large US brokers no longer do for stocks and ETFs).
- Stopping contributions during a downturn defeats the whole purpose: those are the months when your money buys the most shares.
The SEC’s Investor.gov glossary entry gives the official definition.
