Direct answer
Calculate a PERT expected estimate, standard deviation, and variance from optimistic, most likely, and pessimistic values using consistent units.
What to know
- Use consistent units for all inputs.
- Validate zero and negative values before dividing.
- State the forecasting assumption before using an output for a decision.
- Reconcile calculator results with the approved project data date and baseline.
How to apply it
Enter current, controlled project data. Review the formula and model limits before communicating the result, and retain the input values with the analysis.
Formula
Expected = (O + 4M + P) ÷ 6; standard deviation = (P − O) ÷ 6; variance = standard deviation².
Worked example
For O=4 days, M=7 days, and P=16 days, the expected duration is 8 days, standard deviation is 2 days, and variance is 4 days².
Common mistakes
- Mixing currencies or data dates.
- Reporting excessive decimal precision.
- Treating one formula as a guaranteed forecast.
Exam and practice connection
PMP questions can test both calculation and interpretation. Read the wording and identify the requested metric before calculating.