What is Portfolio drift?
Portfolio drift is the slow change in a portfolio's mix that happens when its parts grow at different speeds. A portfolio that starts at 60% stocks can reach 65% or 70% after a strong run for stocks without a single trade. Drift is measured as the gap between the current mix and the target.
Why Portfolio drift matters
Drift changes how much risk you are carrying, and rebalancing is the tool that reverses it.