A deadline is a target date indicating when you want a task to be completed. Imposing an inflexible constraint such as Must Finish On, that sets the finish date can lock up your schedule in ways you don't want. Instead, if you just need a reminder, you can use the deadline field of a task. This will create a green downward arrow on the Gantt chart, that marks the deadline date. The advantage of deadlines is that they keep track of its finish date without locking the schedule.

Apply a deadline to a task when you want to track a deadline for a specific task, but don't want to lock your schedule by setting an inflexible constraint such as Must Finish On or Finish No Later Than. Such constraints affect scheduling, while the Deadline field simply causes an indicator to show if a task has not been completed by its deadline. Certain tasks in your project should finish by specific target dates. However, you don't want these dates to actually affect how Project Plan 365 schedules the tasks; you just want to be alerted if the tasks are not completed by these dates. Add the Deadline field to the Entry table of the Gantt Chart view, and set the deadline dates for these tasks.

By setting a task deadline, instead of imposing an inflexible constraint for a task to mark its finish date, you can achieve a more flexible and dynamic project schedule. A dynamic schedule is properly sequenced and is free of any task constraints. The benefit is that the project manager can assess changes to the project end date (via the critical path) without experiencing constraint errors.

Deadlines can be added to any task in the project schedule. You may want to add specific deadlines based on the tasks on the critical path or on important milestones. The deadline gives you flexibility in setting a commitment date that isn’t tied directly to a baseline finish date.