Blog

Constraints in MS Project

I have heard someone saying that your average 100-line, 3 month schedule will have you spend 50 hours (almost 4 hours per week) on maintenance, if it is not set up right. MS Project should be working for you, not the other way around… Just as in Excel you would not use a Casio next to your calculation model – you would repair the formulas. The first thing you should do is check how you use constraints in MS Project.

Constraints in MS Project are restrictions given to a task or milestone. Examples are:

  • This task cannot start earlier than July 1, 2016
  • This task cannot finish later than August 23, 2016
  • This task must start on January 1, 2016

Using constraints, you can control the start or finish dates of important tasks. It is a useful tool to be able to easily reschedule the project because when you put a constraint on a task in a linked network of tasks, it will effect the whole chain of tasks. MS Project automatically assigns the As Soon As Possible constraint (which actually is not a restriction) when you enter a task (when planning from start date). You should set other constraints only when necessary, because:

  • Constraints will usually decrease the level of schedule flexibility of tasks
  • As the amount of task flexibility decreases also the amount of dynamic behavior of the schedule gets lost

At various stages in your project, you may want to check the constraints on tasks in your schedule, particularly the tasks on the critical path, to make sure they are necessary. For each unnecessary constraint you add 6 manual actions for keeping the schedule up-to-date! Limiting to only the necessary constraints will keep your schedule as dynamic as possible.

Constraints in MS Project are created when:

  • Dates are typed into the start or finish columns or
  • If you double click on a task and change the constraint type in the Advanced tab of the task information window.

If a task has a constraint date attached to it you will immediately see a small calendar in the indicator column. If you hover with your mouse over it, it will tell you the constraint type and date.

Listed below are the types of constraints that exist in MS Project:

Constraints in MS Project

Constraints in MS Project

As constraints in MS Project will limit the dynamicity, your challenge is to avoid these as much as possible. In some cases though you will need them. Consider for instance the following situations:

  • Place the roof, once the supporting walls are finished – You do not need a constraint, but a task dependency.
  • A task can only start once the resource is back from vacation – For this you do need a constraint.
  • However, when you work with resources in your schedule, let the resource calendar reflect the unavailability. ‘As soon as possible’ will then be when the resource has availability again. This is explained in our e-course Maturity Level 4 – Resource Management.
  • End report is due on August 1st, at the latest – Plan ASAP and use a deadline to monitor the due date, not with a ‘finish no later than’ constraint, as you would do when preparing for an exam ;-).
  • End report is due ON August 1st. Same as above, no ‘must finish on’
  • You expect a delivery from a supplier – you do needa constraint to tell MS Project when you receive the goods and can continue working with these goods.
  • You expect a delivery from another project in your organization – you do not need a constraint. You can make a ‘link between projects’ instead. This will be explained in our e-course Maturity Level 3 – Task Management.

Removing constraints

You can easily remove a constraint by double clicking on a task > task information > advanced > constraint type > as soon as possible.

In order to remove a constraint it is not necessary to edit the constraint date field, once you select ‘As Soon As Possible’ MS Project will automatically reset the date according to the task’s predecessor.

If you want to learn more about constraints in MS Project click HERE.

Show us a print screen of your schedule and how you applied constraints? We will tell you what you could improve to save hours. 

Leave a Comment