PERT three-point estimate
Combine optimistic, most likely and pessimistic duration estimates.
Your starting point
LOCAL · PRIVATESample values are filled in. Change them to make this your own.
A little more clarity
RESULTYour result will appear here.
Run the sample to see how it works.Use this tool
- Enter optimistic, most likely and pessimistic estimates in days.
- Ensure they are ordered from smallest to largest.
- Calculate expected duration and spread.
Reading your result
Expected duration is a weighted average. Standard deviation is in days; variance is in days squared. Neither is a deadline guarantee.
How this works
Expected = (O + 4M + P) ÷ 6. Standard deviation = (P − O) ÷ 6.
Use the units shown beside each field. For monetary amounts, use one currency throughout; calculations do not convert currencies. Results normally display up to two decimal places. Nonzero values below 0.01 use up to six significant digits; values below 0.000001 use scientific notation (for example, 1E-7 means 0.0000001). Rankings use unrounded values, so displayed scores can look equal without being tied. CSV downloads retain numeric precision. Monetary rounding uses half-away-from-zero. Inputs or results beyond supported precision are rejected.
Method reference: PMI, Scheduling 101.
Assumptions & limits
Requires O ≤ M ≤ P. A single-task approximation, not a guarantee or a project completion probability.
Required numeric fields reject blank, malformed and out-of-range values; negative values are allowed only for inventory position. Whole quantities are validated where units must be indivisible.
Results are planning aids based on the values you enter. Check important decisions and documents before using or sharing them.
