Egress of data packets from a packet switch is controlled in a manner that involves adjusting the shaper accumulators only when a packet egress event or accumulator credit threshold event occurs. A timeline having a number of timeslots is maintained in a memory to mark the times at which events are predicted to occur. If an egress event occurs, in which one or more data packets have been sent from a queue, or if the current timeslot contains a marker, then a count stored in an accumulator is adjusted. If an egress event has occurred or a threshold event in which a count stored in an accumulator has crossed a threshold has occurred, then a marker is stored in a future timeslot.