Formula
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
- Classical PERT approximation from subjective inputs. No completion probability or independence across tasks is assumed.
Example Calculation
- Optimistic duration: 2 h
- Most likely duration: 5 h
- Pessimistic duration: 8 h
Durations 2,5,8 hours give a PERT estimate of five hours and a one-hour spread.
Frequently asked questions
How do I use this calculator?
Enter optimistic duration, most likely duration, pessimistic duration. The result updates automatically. Use Reset to restore the example values.
What method does it use?
expected=(optimistic+4 likely+pessimistic)/6; spread=(pessimistic−optimistic)/6.. Classical PERT approximation from subjective inputs. No completion probability or independence across tasks is assumed.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.