From the course: Project Management Foundations: Schedules

Determine the critical path - Microsoft Project Tutorial

From the course: Project Management Foundations: Schedules

Determine the critical path

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- [Instructor] The best way to understand the critical path is to calculate activity dates and total float, so you can determine which activities are critical and why. Total float is the time an activity can move earlier or later, without affecting the project finish date. Total float equals an activity's late finish, minus its early finish. Late finish is the latest date an activity can finish without delaying the project finish date. Early finish is the earliest date it can finish. You also calculate total float using late start minus early start. To see how this works, let's calculate part of the example project's critical path. The first step is called a forward pass, which calculates the early start and early finish for every activity. You start at the project start date, and use durations to determine the early starts and early finishes. Writing chapter seven and eight starts on April 28th. Its duration is two weeks, so its early finish is two weeks after April 28th, which is May 11th. For write chapters nine through 12, the early start is May 12th. With two weeks' duration, its early finish is May 25th. Capture screenshots has its early start on May 26th. With one week duration, its early finish is June 1st. Draw illustrations has the same early start and early finish as capture screenshots. The early start for correct manuscript is also May 26th. With two-week duration, its early finish is June 8th, the end of this part of the project. This second step is a backward pass to calculate late start and late finish for activities. The end of this part of the project is June 8th, so the late finish for correct manuscript is June 8th. Subtract its two-week duration and its late start is May 26th. The late finish for capture screenshots is also June 8th. Subtracting one week, the late start is June 2nd. The activity draw illustrations is the same. For write chapters nine through 12, late finish is May 25th. Subtract two weeks and its late start is May 12th. Finally, write chapters seven and eight has a late finish of May 11th. Subtract two weeks' duration and its late start is April 28th, the beginning of this part of the project. The third step is calculating total float. The early and late start for write chapter seven and eight are both April 28th, so its total float is zero. It can't move. It's on the critical path. The same goes for write chapters nine through 12. It's on the critical path too. Capture screenshots has an early start of May 26th and late start of June 2nd. That's five days of total float, so the activity isn't critical and can delay five days. Draw illustrations also has five days of total float. Correct manuscript has the same date for early start and late start, so it's also on the critical path. If an activity's total float is zero, it's on the critical path. Any delay in that activity delays the project finish date. On the other hand, if total float is greater than zero, the activity can delay by that amount without delaying the project finish. Now that you know how the critical path works, you can use it to shorten your project or adjust the schedule.

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