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Intermediate · 2 min read

Schedule constraints

Date pins that override logic — sometimes necessary, often a way to make a schedule say what someone needs it to say.

Working definition

A constraint is a date rule applied directly to an activity — start no earlier than, finish no later than, or the hard "mandatory" versions that override logic entirely. A few constraints are legitimate: contract milestones, permit windows, seasonal limits. But every constraint replaces calculation with assertion, so the count and type of constraints in a schedule is one of the fastest reads on how honest it is.

Key takeaways

  • "Start no earlier than" is the most defensible — it models a real-world gate like access or permits.
  • The recurring pattern in submitted schedules is constraints doing the work logic should do: dozens of pinned dates holding the picture in a shape the network cannot support.
01

The types, from soft to dangerous

"Start no earlier than" is the most defensible — it models a real-world gate like access or permits. "Finish no later than" injects a deadline into the float math and manufactures negative float when the logic cannot reach it. Mandatory start/finish constraints pin dates absolutely: logic can no longer move them, which means the network around them stops meaning anything. P6 will honor them; the forecast quietly stops being a forecast.

02

The abuse pattern to watch

The recurring pattern in submitted schedules is constraints doing the work logic should do: dozens of pinned dates holding the picture in a shape the network cannot support. It shows up as beautiful dates over broken logic — and it is why constraint counts belong in every quality review. When a contractor cannot build the sequence that reaches the date, a constraint is how the date survives review anyway.

The review discipline: every constraint gets an inventory line — what date, what type, whose requirement, still valid? Constraints that cannot be traced to a contract term or a real-world gate should come out, and the logic should be made to carry the plan.

Sources and scope

Follow the reference trail.

This guide is original educational commentary. Kairos reference records identify the source organizations, editions and scope behind this guidance. The original publishers retain their publications and rights.

10S-90: Cost Engineering TerminologyAACE International · checked 2026-08-01Checking schedulesOracle · checked 2026-08-01Schedule Assessment Guide: Best Practices for Project SchedulesU.S. Government Accountability Office · checked 2026-08-01UFGS 01 32 01.00 10: Project ScheduleWhole Building Design Guide / U.S. Department of Defense · checked 2026-08-01