The plan docs and/or the carrier determine when the individual must be removed from the plan. COBRA regulates what happens should the individual lose coverage for certain reasons. The carrier should be asked how long the person must be out before they have to be removed.

If the qualifying event is a reduction of hours, COBRA coverage would begin the day after the benefits termination date. In other words, if the employee has the reduction of hours mid-month, and the carrier says they must be removed on the last day of the month, COBRA coverage would begin on the 1st of the month. The 18 months maximum coverage period will begin on the date of the qualifying event (the termination or reduction in hours).