So you’ve plowed through this chapter, working on dependencies and constraints in your project, and you notice that a successor task’s start date doesn’t match the predecessor’s finish date. You’ve stuck to simple finish-to-start dependencies, so what’s happening?
It’s important to remember that a finish-to-start dependency tells Project only that the successor cannot start before the predecessor finishes. The dependency doesn’t necessarily drive the successor task’s start date.
First, it’s possible that you incorporated lag or lead time between the tasks. It’s also possible that your project is set to calculate manually and you’ve made changes without recalculating your project. Press the F9 key to calculate your project.
Switching from Manual to Automatic Calculation
You can change calculation from manual to automatic using the Options dialog box. On the Tools menu, click Options, and then click the Calculation tab. For the Calculation Mode setting, select Automatic.
Some people prefer to use manual calculation on large projects so that Project doesn’t spend time recalculating the schedule for every change you make. Others prefer to see the effects of every change as it happens. If you find calculation eating up lots of your time, set it to Manual and press F9 when you need to recalculate the schedule.
It’s also possible that the successor task’s start date doesn’t match the predecessor task’s finish date because you set a Must Start On, Must Finish On, Start No Later Than, or Finish No Later Than constraint on the successor task. By default, Project honors constraints over dependencies and so will not move the successor task’s start date based on dependencies.
Project also won’t adjust a successor task’s start date if you’ve recorded any progress on the task. In this case, Project fixes the successor task’s start date as its actual start date.
In cases where you’ve linked two tasks using a finish-to-start dependency, the successor task’s start date could be later than the finish date of the predecessor task because:
The successor task has two predecessors and one is longer than the other; in this case, the successor task’s start date will be driven by the finish date of the predecessor that finishes latest.
You’ve set a Start No Earlier Than constraint or a Finish No Earlier Than constraint on the successor task.
The successor task is a subtask of a summary task and you’ve set a constraint, a dependency, or both on the summary task that forces the summary task’s start date.
That last reason, by the way, is one more good reason not to set constraints or dependencies on summary tasks.