Definition
The share of booked appointments where the customer never arrives, usually tracked as a percentage of appointments scheduled over a period. For appointment-based businesses (med spas, salons, clinics, studios) it is a direct revenue leak, because the reserved time and the staff assigned to it are already paid for.
What it looks like in practice
Thursday at two is a ninety-minute laser appointment at a med spa. Three days out, the client gets a text confirming the date and asking her to reply yes or reschedule. She does not reply, so a second message goes the next morning. Wednesday afternoon she replies reschedule, which frees Thursday at two with a day of notice. The wait-list flow starts: everyone who wanted that treatment this week gets one text, first reply takes the slot, the rest are told it went. A client who was booked for the following month moves up. The provider works a full Thursday instead of an unpaid gap.
Why it matters
What makes a no-show expensive is that the inventory is perishable. A two o'clock slot that goes empty cannot be sold later, cannot be stocked, and cannot be made up; the room was held, the provider was on the clock, and the hour is simply gone. That is why confirmation and wait-list flows tend to be the first thing worth automating on a booked calendar: the same reminders sent by hand get skipped on busy days, which is exactly when the calendar is fullest. The limit is notice. A cancellation an hour out rarely refills, so the goal is pulling the answer forward, not just recording who missed.