What is dollar cost averaging, and does it work?

Dollar cost averaging means investing a set amount at regular intervals rather than all at once, which buys more shares when prices are low and fewer when high. The evidence on whether it outperforms is fairly clear and cuts against the folklore: studies including widely cited Vanguard research have found that investing a lump sum immediately beats spreading it out roughly two thirds of the time, because markets rise more often than they fall and time in the market is the dominant variable. Averaging in means holding cash that is, on average, missing returns.

The case for it is behavioral and situational rather than mathematical, which does not make it worthless. It reduces the risk of the worst-case timing, investing everything the week before a sharp decline, and more importantly it reduces the odds that an investor panics and abandons the plan, which is the failure that actually destroys returns. If averaging in is what allows someone to invest at all, it beats the optimal strategy they will not follow. It also describes what most people do automatically, since contributing from each paycheck to a retirement account is dollar cost averaging by construction rather than by choice, and that is the version that matters most. The honest summary: if you have a lump sum and a long horizon, investing it now is the higher-expected-value move, and averaging in over a few months is a reasonable price to pay for sleeping through the decision.