The Principle and Limits of Dollar-Cost Averaging (DCA)
"Buy steadily every month and your average price goes down." That is DCA. But is this strategy always best? Mathematically, it may not be.
What Is DCA?
DCA (Dollar-Cost Averaging) is a method of investing a fixed amount regularly, regardless of market conditions.
Example: buying an ETF for about $74 each month. When the price is high you buy fewer shares, and when it is low you buy more. As a result, your average purchase price is lower than the simple average price. This is the "dollar-cost averaging" effect.
The most important advantage is psychological stability. You don't have to agonize over when to buy, and you can avoid the mistake of dumping everything in at a peak.
DCA vs. Lump-Sum: A Mathematical Comparison
An interesting fact: if you already have the money, lump-sum investing is on average mathematically more advantageous than DCA.
According to a Vanguard study (2012, using U.S., U.K., and Australia data), lump-sum investing produced a higher return than 12-month DCA in about two-thirds of cases. The reason is simple. Because the stock market tends to rise over the long run, the sooner you invest, the longer you enjoy the compounding effect.
However, DCA has a psychological advantage. It reduces losses in a down market and eases anxiety about investment timing.
When investing regularly from your salary, you are not in a "money already on hand" situation, so DCA is the natural choice.
The Real Value of DCA: Behavioral Economics
Despite its mathematical inferiority, there is a reason DCA can produce better results in reality.
When investing a lump sum, many investors worry "what if this is the peak?" and fail to actually execute. Or they panic-sell right after a decline. DCA lowers these psychological barriers.
In practice, "executing the second-best strategy perfectly" yields better results than "executing the optimal strategy poorly." This is why DCA is still recommended.
よくある質問
Q. How often should I invest?
In theory, the more often you invest, the greater the average-price smoothing effect, but there is a trade-off with transaction costs. In most cases, once a month strikes a good balance of cost and effect. Since Korean ETF trading commissions are as low as about 0.015%, even once a week is not a heavy burden.
Q. What should I do if a crash comes during DCA?
The heart of DCA is to keep investing regardless of market conditions. In a crash, the same amount buys more shares, which actually becomes an opportunity to lower your average price. If you stop investing during a crash, DCA's core advantage disappears. That said, if the investment amount threatens your living expenses, it is right to reduce the size of your investment.
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