Project Constraints

Microsoft Project Scheduling Constraints

In Microsoft Project constraints can be used to create a link between a task and a particular date. By choosing a Constraint Type you can set how Microsoft Project constrains the start or finish dates of a given task.
By default all tasks are created with the Constraint type 'As Soon As Possible'. This allows Microsoft Project to schedule a task on the basis of its duration, resource(s) and dependencies, rather than against a particular date.

What are the Constraints types in Microsoft Project?

There are eight constraint types in Microsoft Project:
  • As Soon As Possible
  • As Late As Possible
  • Finish No Earlier Than
  • Finish No Later Than
  • Must Start On
  • Must Finish On
  • Start No Earlier Than
  • Start No Later Than
How to create project constraints

Why would you set a Constraint?

Sometimes you need to prevent Microsoft Project from rescheduling a task away from a key date. For example, imagine you are managing the delivery of a conference. The date of the conference is likely to have been booked for months and is probably immovable. In this instance you might set a ‘Must start on’ project constraint for the date of the conference.

Must Start on Project Constraint

Assuming ‘Conference day’ has other tasks linked to it (it should), Project will warn you that a constraint might cause a future scheduling conflict.

Project Constraint warning

That is fine because if one of the tasks linked to the Conference day takes longer than planned then we need to know if it will conflict with the Conference start date.

Lets say that Arranging the AV equipment was planned to take 2 days, but we find that actually it will take 6 days. If we increase the duration to 6 days Microsoft Project will warn us that there is a scheduling conflict (see below).

Project Scheduling Conflict warning

So Project Constraints can be useful and have a valid part to play in project planning. However, they can also be created by mistake with dangerous knock on effects. In part 2 see how accidentally setting constraints can impact your project plan.

Project Constraints part 2 - common mistakes.

Read more guides on using Microsoft Project