Project the completion dates from the effort estimates in the queue of work remaining to be done
As work progresses, a better picture of a realistic schedule for completion can be built. This is as a result of the better understanding of the complexity of the remaining work, the rate of progress to date, the reduction in the amount of remaining work, and the revised estimates for the effort needed to complete the remaining work. The Completion Headroom is the difference between the projected completion date and the scheduled completion date. It is also useful to track changes over time in the Completion Headroom, in case there are consistent trends. A negative Completion Headroom implies the need for some rescheduling.
There is a reasonable discussion at the bell-labs source site. Obtain estimates using ComparableWork for work remaining on the WorkQueue (if using that approach, otherwise for tasks on the schedule). When rescheduling is needed, consider the pattern TakeNoSmallSlips. Rescheduling may be done by performing a WorkSplit; or a RecommitmentMeeting may be necessary.