While you deliver
Critical Path Calculator
Find the chain of work that sets the finish date, how much room everything else has, and what a proposed change would do to the date, from a schedule you type or the file your scheduling software already has.
Type or paste a schedule, or open a Microsoft Project XML export, a Primavera P6 XER file, or a .xlsx or .csv, inside your browser. Nothing is uploaded.
Working calendar Monday to Friday, US federal holidays, weekend holidays moved to the nearest working day change
The activities
Predecessors by ID: 3, or 3FS+2 for a two-day lag, 5SS, 7FF-1 for a lead. Separate several with semicolons. A duration of 0 is a milestone.
| ID | Activity | Days | Predecessors | Constraint | Constraint date | Cost | People | Remove |
|---|---|---|---|---|---|---|---|---|
Settings: near-critical 5 days, lags on the successor’s calendar
What the critical path is, and why it moves
Every schedule has a chain of activities with no room in it: delay any one of them and the finish moves by the same amount. That chain is the critical path. Everything else has float, room to slip before it matters. The tool works out both the standard way: a forward pass for the earliest each activity can start and finish, a backward pass from the finish for the latest, and the difference is float. When an activity slips or the logic changes, the path can jump to a different chain, which is why it is worth recalculating rather than remembering.
Real schedules, not textbook ones
Free critical path calculators mostly take a handful of finish-to-start links typed into a box. Real schedules have start-to-start and finish-to-finish links, leads and lags, holidays, activities on different calendars, date constraints and work already under way. All of that is handled here, and a schedule can come straight from Microsoft Project (saved as XML) or Primavera P6 (exported as XER), read in the browser without the software.
Where the two packages disagree, it says so
Microsoft Project counts a lag on the successor’s calendar; Primavera, by default, on the predecessor’s. Project and Primavera treat work that started out of sequence differently. Durations of part of a day do not fit a whole-day schedule. Each of these is a setting or a stated convention, and when the dates worked out here differ from the dates saved in the file, the tool counts the activities that differ and gives the likely reasons, rather than presenting one set of dates as the truth.
Negative float is a deadline the logic cannot meet
A date constraint such as “finish no later than” can ask for something the logic cannot deliver. The result is negative float: the number of working days the plan is short. The sample shows it: a lease that requires moving in four working days before the work can be done. The honest answers are to change the logic, add resources to critical work, or move the date; the tool shows which activities carry the shortfall so the conversation can start there.
What if
Before a change is approved, add it: a piece of work after one activity and before another, or a new duration for an existing one. The tool reruns the schedule and shows how far the finish moves, which other activities move, and what happens to the total cost and the peak number of people working at once. A change that lands on float can cost nothing in time; the same change on the critical path moves the date day for day.
What this does not do
It does not level resources: two activities that need the same person can be scheduled at once. It works in whole days, so it is not the tool for a schedule measured in hours. It reads Project’s XML export, not the .mpp file itself, which only Project can open. And it does not decide what to do about the critical path; it shows where it runs.