Schedule & Critical Path / analysis brief
Float and slack: find the schedule’s real room
Enter early and late start and finish dates to calculate total float, cross-check the backward pass, and optionally measure free float before the successor moves. The guide explains zero and negative float, date conventions and how to protect the critical path.
Live reading
Calculator workspace
Enter a current project reading to update this decision signal.
1 — Float (slack)
Total float · free float · critical path test
Total float is how long an activity can slip without delaying the project finish. Free float is how long it can slip without delaying its immediate successor. Zero total float means the activity is on the critical path. Enter the dates from your forward/backward pass — either day numbers or durations, as long as they are consistent (this calculator uses the continuous convention where EF = ES + duration).
Total Float = LS − ES = LF − EF
Free Float = ES(successor) − EFParameters
- ES — Early Start
- The soonest the activity can start, from the forward pass.
- e.g. 5
- EF — Early Finish
- The soonest it can finish: ES + duration.
- e.g. 9
- LS — Late Start
- The latest it can start without delaying the project, from the backward pass.
- e.g. 8
- LF — Late Finish
- The latest it can finish without delaying the project.
- e.g. 12
- Successor ES (optional)
- Early start of the next activity — only needed for free float.
- e.g. 11
Results
- Total float
- Slip allowance before the project end date moves: LS − ES.
- Cross-check (LF − EF)
- Should equal LS − ES; a mismatch means a pass was computed inconsistently.
- Free float
- Slip allowance before the next activity is disturbed: successor ES − EF.
Charts
- Early vs late window
- How much room the activity has before it becomes critical.
What float (slack) actually answers
+Float shows how much schedule flexibility a task has under a defined network.
Start with a clean definition. State the unit, time window, and whether each figure is planned, actual, or forecast. A result can be mathematically correct and still be operationally wrong when a team mixes calendar days with working days, approved budget with total cost, or a current snapshot with a period-to-date value. The calculator is transparent: change an input and watch the output move, then explain why it moved.
For a worked reading, enter the example values above and write down the intermediate meaning before interpreting the verdict. First identify the baseline. Next identify the observed performance, probability, or variation. Then calculate the derived measure. Finally ask whether the direction and size of the result justify an action. This order keeps arithmetic from becoming a substitute for project judgment.
Use the result as a signal in a control loop. If the reading is favorable, confirm that scope and quality have not been reduced to create a better number. If it is unfavorable, investigate the cause before prescribing a generic recovery action. A late schedule may reflect changed scope, a poor dependency, or a bad estimate. A risk score may reflect disagreement about scales rather than a change in exposure.
Uncertainty deserves an explicit sentence. Forecasts are conditional on their assumptions, and rankings are relative to the set of items being compared. Add a range where inputs are estimates, show sensitivity where one assumption dominates, and agree what evidence will cause the team to revise the reading. This makes the page useful for governance rather than just for producing a polished percentage.
Common mistakes are classification mistakes. People use a ratio as a percentage, add probabilities that belong to different branches, treat a reserve as a forecast, or compare values calculated with different boundaries. Another frequent error is false precision: reporting several decimal places when inputs were rough workshop estimates. Round for the audience, but keep the full browser calculation for traceability.
On a real project, pair the result with an owner and a next action. A metric without a response path is decoration. Decide who validates the inputs, who discusses the implication, and when the number is checked again. If the result crosses a threshold, define escalation before pressure arrives. If it remains stable, say what stable means and how long that conclusion may stand.
For exams and formal methods, use the stated formula and assumptions. For practice, add context the question leaves out: baseline changes, data quality, dependencies, stakeholder tolerance, and the cost of waiting. The best professional answer can be more cautious than the best multiple-choice answer. That is not indecision; it is disciplined interpretation.
Keep a small decision record with input values, date, source, result, interpretation, and action. When the project changes, do not overwrite history. Compare the new reading with the old one and explain the movement. This turns a one-time calculation into evidence about the system and gives a future project manager enough context to learn from the forecast instead of repeating its assumptions.
For a worked reading, enter the example values above and write down the intermediate meaning before interpreting the verdict. First identify the baseline. Next identify the observed performance, probability, or variation. Then calculate the derived measure. Finally ask whether the direction and size of the result justify an action. This order keeps arithmetic from becoming a substitute for project judgment.
For a worked reading, enter the example values above and write down the intermediate meaning before interpreting the verdict. First identify the baseline. Next identify the observed performance, probability, or variation. Then calculate the derived measure. Finally ask whether the direction and size of the result justify an action. This order keeps arithmetic from becoming a substitute for project judgment.
For a worked reading, enter the example values above and write down the intermediate meaning before interpreting the verdict. First identify the baseline. Next identify the observed performance, probability, or variation. Then calculate the derived measure. Finally ask whether the direction and size of the result justify an action. This order keeps arithmetic from becoming a substitute for project judgment.
For a worked reading, enter the example values above and write down the intermediate meaning before interpreting the verdict. First identify the baseline. Next identify the observed performance, probability, or variation. Then calculate the derived measure. Finally ask whether the direction and size of the result justify an action. This order keeps arithmetic from becoming a substitute for project judgment.
For a worked reading, enter the example values above and write down the intermediate meaning before interpreting the verdict. First identify the baseline. Next identify the observed performance, probability, or variation. Then calculate the derived measure. Finally ask whether the direction and size of the result justify an action. This order keeps arithmetic from becoming a substitute for project judgment.
For a worked reading, enter the example values above and write down the intermediate meaning before interpreting the verdict. First identify the baseline. Next identify the observed performance, probability, or variation. Then calculate the derived measure. Finally ask whether the direction and size of the result justify an action. This order keeps arithmetic from becoming a substitute for project judgment.
For a worked reading, enter the example values above and write down the intermediate meaning before interpreting the verdict. First identify the baseline. Next identify the observed performance, probability, or variation. Then calculate the derived measure. Finally ask whether the direction and size of the result justify an action. This order keeps arithmetic from becoming a substitute for project judgment.
For a worked reading, enter the example values above and write down the intermediate meaning before interpreting the verdict. First identify the baseline. Next identify the observed performance, probability, or variation. Then calculate the derived measure. Finally ask whether the direction and size of the result justify an action. This order keeps arithmetic from becoming a substitute for project judgment.
For a worked reading, enter the example values above and write down the intermediate meaning before interpreting the verdict. First identify the baseline. Next identify the observed performance, probability, or variation. Then calculate the derived measure. Finally ask whether the direction and size of the result justify an action. This order keeps arithmetic from becoming a substitute for project judgment.
Worked through end to end
Enter the example values shown in the instrument, note the baseline, and read each output in the unit displayed. The point is to make the calculation reproducible, not to imply that one example predicts every project.
Step 1
Validate the inputs, read the derived result, and record the action it supports.
How to read the result
Interpret the verdict alongside scope, data quality, dependencies, and the date of the reading. The metric stops being useful when those boundaries are hidden or when a team treats a signal as a guarantee.
Mistakes that survive into real reporting
The most damaging mistakes are mixed units, stale baselines, false precision, and decisions made without an owner or review date. Keep the inputs and assumptions visible.
On the exam and on a real project
Use the formal method for a consistent answer, then add practitioner context: assumptions, uncertainty, stakeholder tolerance, and the cost of waiting.