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Hard Constraint

Hard Constraint

Scheduling Terms Reviewed by forProject Technology - updated Sep 2026
Quick definition: A Hard Constraint is a Constraint that limits how late a task or milestone can start or finish, or imposes a specific date, and so can inhibit the logical flow of the schedule.

A Hard Constraint sets a limit on how late a task can start or finish, or may impose a specific start or finish date. Hard Constraints can therefore inhibit the logical flow of the schedule and can lead to Negative Float. In Microsoft Project, examples include Start No Later Than (SNLT), Finish No Later Than (FNLT), Must Start On (MSO), and Must Finish On (MFO). Other scheduling tools, like Primavera P6, use different terms for these kinds of Constraints.

What this means for you

A Hard Constraint holds its date even when the schedule logic and Durations would push the task to different start or finish dates. When the task can't meet that date, the schedule shows Negative Float, a sign that key dates are unachievable. Used too often, Hard Constraints keep the schedule from showing how delays really affect the Critical Path.

Also known as
N/A
Used in
Network Schedule construction; Critical Path Method calculations

FAQ

Can a Hard Constraint move a task earlier than its logic allows?
Yes. A "Must Start On" or "Must Finish On" Constraint can force a task to start or finish earlier than its logical links and Duration would allow.
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