Threshold rebalancing
Returning to target weights only once a class has left its allowed band: the trigger is the size of the drift, not the arrival of a date.
How to read the number
It caps the deviation rather than the time between trades: the portfolio cannot wander further from plan than the band allows, however long a rally lasts.
When the metric lies
On a choppy market the band is breached often, and costs plus the tax event from each review eat the gain from precision. Band width is a trade-off, not a setting where narrower is better.
Also known as: tolerance band rebalancing