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Constraint

Constraint

Scheduling Terms Reviewed by forProject Technology - updated Sep 2026
Quick definition: In scheduling, a Constraint is a date limit placed on a task or milestone, such as "start no earlier than" or "finish no later than" a given date.

Normally, a task's dates are calculated based on the logical links to other tasks and its Duration. A Constraint adds a date limit on top of those links. Soft Constraints limit how early a task can start or finish, without inhibiting the logical flow of the schedule. Hard Constraints limit how late a task can start or finish, or impose a specific date, and so can inhibit the logical flow of the schedule. In broader project management, "constraint" can also mean any factor that limits a project's options, such as budget or available resources.

What this means for you

Constraints allow a schedule to reflect real date limits, such as when key information will be available or the day a test facility will become available. However, imposing Hard Constraints can inhibit the logical flow of the schedule, distorting the Critical Path calculations and making the calculated dates in the schedule less reliable. Imposing dates with Hard Constraints can lead to Negative Float, which is an indication that key dates in the schedule are unachievable. See Hard Constraint for additional detail.

Also known as
Date Constraint
Used in
Network Schedule construction; Critical Path Method calculations

FAQ

When should a Constraint be used?
Only when a real date limit exists that the schedule's logic can't capture, such as when key information will be available. Otherwise, it's better to let the logical links and Durations set the dates.
Can a Constraint cause Negative Float?
Yes. A Hard Constraint can set a date the task can't meet given its logical links and Duration. When that happens, the schedule shows Negative Float, which flags the conflict.
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