Inside Out: Beware of entering dates

If you enter a date in the Start field (in a project scheduled from the start date), the Start No Earlier Than constraint is applied. The finish date is recalculated based on the new start date and the existing duration.

If you then enter a date in the Finish field of the same task, the constraint changes to Finish No Earlier Than. The start date remains as you set it, but the duration is recalculated to reflect the difference between your entered start and finish dates.

These kinds of constraints can prevent your schedule from taking advantage of time saved by a task finishing earlier than expected. For example, suppose that the 8-day task "Construct walls" is scheduled to finish on October 3. It is the predecessor to the "Plaster walls" task which has a Start No Earlier Than constraint of October 4. If the "Construct walls" task finishes 2 days early, on October 1, the schedule for the "Plaster walls" task does not change to October 2, but maintains that the task not be started until October 4.

Always be aware that any dates you enter change the As Soon As Possible or As Late As Possible constraints to something more inflexible. If you enter both the start and finish dates for a task, Microsoft Project recalculates the duration.

Entering your own start and finish dates imposes often unnecessary restrictions on the capability of Microsoft Project to create the best possible schedule. It can also adversely affect results when you have Microsoft Project level overallocated resources. In the majority of cases, you get the best results when you enter durations and task dependencies and then let Microsoft Project figure out the best start and finish dates for tasks to be done as soon as possible. Use date constraints only when there is a specific calendar date that you must work toward, such as an event or a fixed deliverable due date that has no possibility of changing.

Project Management Practices: Working with Date Constraints

When developing your project schedule, you might contend with one of two major categories of date constraints: externally imposed dates and milestone dates.

An externally imposed date reflects situations outside the project that influence the project schedule. Examples include the following:

You can reflect externally imposed dates as constraints on the tasks they affect. You can also add a task note as a reminder of the source of this date.

Milestone dates are typically dates set internally, often used to mark the end of phases or "chunks" of work in your work breakdown structure. As the project manager, you might set them yourself as goals to work toward. The project sponsor, customer, or other stakeholder might request certain dates for certain milestones, deliverables, or events being produced by the work of your project. You can set constraints on milestones as well as on regular tasks.

Change Constraints for Multiple Tasks at Once

In a task sheet, select all the tasks that will have the same constraint applied. Drag across adjacent tasks to select them or hold down Ctrl while clicking nonadjacent tasks. Click Task Information on the Standard toolbar and then click the Advanced tab in the Multiple Task Information dialog box. Change the Constraint Type and, if applicable, the Constraint Date. Click OK. The constraint is changed for all selected tasks.

This method works best if you’re changing date constraints to As Soon As Possible or As Late As Possible because it’s rare for multiple tasks to have the same constraint date.

Troubleshooting

You can’t delete a constraint

By their nature, constraints are not deleted. A constraint is applied to every task. If you’re thinking of deleting a constraint, what you probably want to do is change it from a date constraint such as Must Start On or Finish No Later Than to a flexible constraint such as As Soon As Possible.

Double-click the task to open the Task Information dialog box and then click the Advanced tab. In the Constraint Type box, click As Soon As Possible or As Late As Possible.