PERT Path Duration and Deadline Calculator
Combine three-point task estimates into a fixed serial path’s expected duration, variance and normal-approximation deadline probability.
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Result
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Calculation steps
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How to calculate
Use the PERT three-point mean/variance per task and add independent path moments before the deadline approximation.
Task mean=(a+4m+b)/6; task variance=((b−a)/6)²; path SD=√Σvariance
Worked example
Tasks (1,2,3) and (2,3,4) days have expected serial duration 5 days and SD √(2/9)≈0.471405 days. A deadline equal to the mean has normal-approximation probability 0.5.
Assumptions and input details
1–200 tasks with nonnegative ordered optimistic≤most likely≤pessimistic estimates. One fixed serial path and independent task uncertainties are assumed. This does not solve changing critical paths or a complete project-network completion distribution. Resource conflicts, correlations and empirical duration validation are excluded. Zero total variance gives a deterministic deadline comparison rather than a normal z statistic.
Unit definitions
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Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
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The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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