What Is Dollar-Cost Averaging?
Dollar-cost averaging (DCA) means investing a fixed amount of money on a fixed schedule, regardless of the price at the time, rather than trying to time the market with a single lump-sum purchase. Buy $500 of a stock every month, for example, whether the price is high or low that particular month.
The effect: a fixed dollar amount buys more shares when the price is low and fewer shares when the price is high. Over time, this tends to pull your average cost per share below the simple average of the prices you bought at, which is the core mathematical case for DCA as a strategy.
The DCA Average Price Formula
Each round, the number of shares you receive is your fixed investment amount divided by that round's price. Your overall DCA average price is your total money invested divided by the total shares you ended up with, not a simple average of the prices.
Shares per round = Amount invested ÷ Price that round
DCA Average Price = Total Amount Invested ÷ Total Shares Owned
Simple Average Price = (P1 + P2 + ... + Pn) ÷ n (not the same number)Notice the DCA average price formula is mathematically identical to the weighted average formula used for any set of stock purchases. DCA is really just a specific, disciplined pattern of purchases (same amount, regular schedule) rather than a different formula.
Real Numbers, Step by Step
Investing $500 a Month for Three Months
| Round | Amount Invested | Price / Share | Shares Bought |
|---|---|---|---|
| Month 1 | $500 | $50 | 10.00 |
| Month 2 | $500 | $40 | 12.50 |
| Month 3 | $500 | $62.50 | 8.00 |
| Total | $1,500 | N/A | 30.50 |
DCA average price = $1,500 ÷ 30.50 shares = $49.18 per share
The simple average of $50, $40, and $62.50 is $50.83. Your actual DCA average price, $49.18, is lower, because Month 2's low price bought you 12.50 shares (the most of any round), pulling the weighted result down.
DCA vs. Averaging Down: They're Not the Same
Dollar-cost averaging is a pre-committed, scheduled strategy: you invest the same amount on the same cadence no matter what the price does. Averaging down is a reactive, discretionary decision, buying more of something specifically because its price dropped, which only makes sense if your reasons for owning it in the first place still hold true.
Our Stock Average Calculator covers averaging down and up in depth, including when averaging down can be a value trap rather than a bargain. If you're deciding between a scheduled DCA plan and a one-off averaging-down purchase, that's the right place to think it through.