Quote:
Originally Posted by mtgordon
Yeah, I could see averaging by units. That makes more sense.
On your example, why does DCA get to buy at $75 the first year but lump sum has to buy at $100?
$100 is the start year, they both pay that price initially, $75 is year 2. But it doesn't always have to be lower, let's do it with every year higher than the first, i.e. $100, $150, $200, and finishing at $300.
DCA buys 1 unit, .67 units, .5 units for 2.17 units total, and an average holding period of 3 + 1.33 + .5 unit years, or 4.83/2.17 = 2.25 years. Total return is 2.17x over 2.25 years or 41% annualized.
Lump sum is the same 44%, so DCA slightly trails in this example. But it also shows you how hard it is to find examples where DCA trails, essentially the market has to go up and up and never retrench or even flatten for lump sum to win.
For example let's do it again with one minor tweak in making year 3 $150 just like year 2. Now DCA buys 1 unit, .67 units, & .67 units for 2.33 units total. Averaging holding period is 3 + 1.33 + .67 = 5/2.33 = 2.14 years. Total return is 700/300^2.14 or 48.6% annualized.
DCA often wins even when the market doesn't drop during the investment periods, because the fluctuations and flat points mean that the annualized returns from those points often exceed the returns from the beginning point. I think the worst market for DCA vs. lump sum would be one where the first year returns are the highest in the series, and the rest of the series still offers positive returns but small ones.
But in the end it's a meaningless "competition", we rarely if ever choose between investing via DCA and lump sum. It's just nice to know that DCA offers great benefits to passive investors over long periods in almost every market.