Critical Path Calculator (CPM Lite)

Float (also called slack) is the number of days a task can be delayed without pushing out the project's finish date. A task with 5 days of float can start up to 5 days late and still finish on time. Total float is calculated as LS − ES (or equivalently LF − EF). Tasks with zero float are on the critical path.

A critical task is one with zero float — if it slips by a day, the project end date slips by a day too. The critical path is the longest connected chain of these zero-float tasks. Field teams often focus all their daily coordination on critical path tasks because that's where every hour of delay turns directly into schedule overrun.

This tool handles only finish-to-start dependencies, no calendars (every day counts — no skipping weekends/holidays), no resource constraints, no progress percent updates, and no baselines for variance reporting. Primavera P6 and MS Project layer in calendars, resource leveling, lag/lead, four relationship types (FS/SS/FF/SF), earned value, and contractually-required baseline submittals. This tool is great for sketching and learning CPM; specs-required scheduling needs the full software.

Lag (waiting time between predecessor finish and successor start, e.g. concrete cure) and lead (overlap, e.g. start drywall while framing is still finishing the last room) aren't modeled in this lite tool. As a workaround, add a dummy task to represent lag (e.g. "Concrete Cure — 7d") or split a task into stages to enable overlap. For production scheduling with native lag/lead support, you need P6, MS Project, or similar.