Hard and Soft Constraint Indicators in Web Access

Written on . By Tracy Mah

Constraints in P6 are used to control and adjust the schedule to meet real world requirements. You can use constraints to control the entire project (Project Constraints) or individual activities (Activity Constraints).

Constraints can also be categorized as hard or soft. Hard Constraints are used to reflect real dates that must be met in the schedule. Hard Constraints can override scheduling logic. For example, a stakeholder will indicate the finish date of the project that will never change. The Must Finish By date affects only the backward pass calculation and therefore indicates critical activities and the float of the project. In addition, hard constraints such as Mandatory Start or Mandatory Finish will override scheduling logic (your forward and backward pass calculations) by pushing dates backwards and forwards into the schedule.

Soft Constraints are used to create parameters for when an activity within a project can start or finish. These constraints allow activities to move within the project, but they can create negative float if the activity start or finish does not meet the soft constraint. For example, material will not be delivered to the site until a specific date so the project manager will set a Start On or After constraint on that activity to reflect when labourers will be able to start work on the activity.

Below, we have listed the project and activity constraints in P6 and categorized them as either Hard or Soft Constraints. 

1) Project and Activity Constraints categorized as Hard or Soft Constraints:

Project vs. Activity Constraints

2) Hard and Soft Constraints categorized as either Project or Activity Constraints:

Graph 2


How to Check Hard and Soft Constraints in P6 Web:

If you are looking to check your schedule for hard and soft constraints in P6 Web Access, follow these quick and easy steps:

1)     Click on the Action menu, Run, Check Schedule.


2)     Select only Hard Constraints – Constraints that prevent activities being moved and Soft Constraints – Constraints that do not prevent activities being moved. Click Check Schedule.


You can set a target of how many activities hard and soft constraints affect in your project. In this case, we have indicated that less than 1% of activities can be affected by hard constraints and less than 5% of activities can be affected by soft constraints. The number of activities affected will vary by the size and complexity of the project.

It is always a best practice that you limit the amount of constraints in your project so that you do not complicate your schedule. It is also recommended that you limit the number of hard constraints in your project to 1-2% because these types of constraints can override scheduling logic and create scheduling errors.

3)     View the Hard and Soft Constraints in the project.