The logic of dollar-cost averaging is plain enough — stop trying to catch the bottom, buy a fixed amount on a fixed schedule, and let discipline stand in for the panic-buying and fear-selling wired into all of us. But there's more craft in the "how" than people expect.
The most compared pair is weekly versus monthly. Plenty of folks lose sleep over this, yet over a long enough stretch the gap in annualized return is often tiny — usually within a single percentage point. You agonize for ages and the savings might amount to one bubble tea. The real separator is the third style: valuation-guided DCA, sometimes called smart DCA. The idea is to buy more when the market is cheap and ease off or pause when it's pricey. That's basically loading up on shares in the undervalued zone, and over time it usually beats mindless equal amounts — though it demands you be willing to go against the crowd.
So how do you actually know if your DCA is working? Here's the trap: a lot of people just take "total invested versus current value" and call it a return, but that number lies, because it pretends every dollar went in on the same day. Money you put in three years ago and money you put in last week have borne totally different amounts of volatility. XIRR fixes this by factoring in exactly when cash flowed in and out, handing you an annualized return you can defend. So don't just stare at "I'm up 30% total" — look at "by my real cash flows, what's the annualized number?" The total may be green, but if the bulk of it arrived recently, your true annualized return could be far less flattering.