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PERT Calculator


The PERT calculator helps you predict the completion time of your project with a high degree of accuracy. It considers the optimistic, pessimistic, and most probable time estimations to provide a more accurate project timeline. 

How to use our PERT calculator?

Enter the values of the Optimistic, Pessimistic, Most Probable, and optionally your Desired Completion estimates into the given section

Set the PERT and Standard Deviation in required units

Hit on the Calculate button

The tool will instantly process the information and will show you the completion time of your project along with the Standard Deviation and the Probability of completion results.

What is PERT in project management?

PERT stands for Program Evaluation and Review Technique, is a project management methodology used to calculate the time required to complete a project realistically.

It is particularly useful for projects that involve a high degree of uncertainty and variability in task completion times. Therefore it helps project managers and team members in planning projects to meet their target completion timelines by considering the best-case, worst-case, and most likely scenarios.

PERT formula:

The formula for calculating the PERT is:

\(TE = \frac{{TO + 4 \times TM + TP}}{6} \)


  • TE – Expected Time
  • TO – Optimistic Time (shortest possible time in which a task can be completed)
  • TM – Most Likely Time (best estimate of the time required for a task under normal working conditions)
  • TP – Pessimistic Time (longest time that a task might take under adverse conditions)

When you are calculating PERT, it's helpful to consider the Standard Deviation, which is usually written as SD. This SD gives you an idea of how accurate your calculation is, it means you can plan even better. 

For instance, you can tell your customer a range of time within which the project is likely to be completed. To calculate the standard deviation, use the following formula:

\( SD = \frac{{P - O}}{6} \)

You can skip these manual calculations to save your time by using this PERT calculator offered by the Calculatored.

Example of using the PERT formula:

let's say you are estimating the time it'll take to write a report, and you have the following information:

  • Activity name: Write a Report
  • Optimistic time (TO): 2 days
  • Most likely time (TM): 4 days
  • Pessimistic time (TP): 6 days

Using the formula:

TE = (TO + 4 * TM + TP) / 6

Now, add these values to the formula and calculate:

  • TE = (2 + 4 * 4 + 6) / 6
  • TE = (2 + 16 + 6) / 6
  • TE = 24 / 6
  • TE = 4 days

Therefore, based on the given estimates, the expected duration for writing the report is 4 days.

The standard deviation (SD) for the PERT estimate is:

SD = (TP - TO) / 6

Using the same information from the previous example:

  • Optimistic time (TO): 2 days
  • Pessimistic time (TP): 6 days

Now, add these given values into the formula:

  • SD = (TP - TO) / 6
  • SD = (6 - 2) / 6
  • SD = 4 / 6
  • SD = 2/3 days (approximately 0.67 days)

Therefore, the standard deviation for the expected duration of writing the report is approximately 0.67 days. This indicates a potential variation of roughly 0.67 days above or below the expected duration of 4 days.