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PERT Three-Point Schedule Estimate — result sheet
Combine optimistic, most-likely, and pessimistic task durations into a weighted expected time, spread, and variance for early project planning.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Expected time te = (optimistic + 4×most likely + pessimistic)/6; standard deviation = (pessimistic−optimistic)/6; variance = standard deviation².
PERT gives the most-likely estimate four times the weight of each endpoint in this common three-point approximation. The spread is a planning signal, not a promise that project durations follow a perfectly known probability distribution.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Optimistic duration — days; minimum 0; maximum 1000000000
- Most-likely duration — days; minimum 0; maximum 1000000000
- Pessimistic duration — days; minimum 0; maximum 1000000000
Worked example
| Input | Value |
|---|---|
| Optimistic duration | 2 |
| Most-likely duration | 4 |
| Pessimistic duration | 10 |
Expected duration ≈ 4.667 days, standard deviation ≈ 1.333 days, variance ≈ 1.778 days².
Assumptions and limits
- The optimistic, most-likely, and pessimistic inputs describe the same task and unit.
- The pessimistic estimate must not be below the optimistic estimate for the spread to represent a range.
- Dependencies, resource contention, critical-path structure, correlation between tasks, and schedule risk events are not modeled.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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