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Planning · Free browser tool

Free PERT Estimate Calculator

Combine optimistic, most likely and pessimistic estimates into a weighted planning estimate.

Updated

What does this calculator do?

PERT uses three duration estimates to make uncertainty explicit instead of relying on a single optimistic deadline.

Calculate your result

Free · No account required

Use hours or days consistently.

Your central estimate in the same unit.

Your plausible high estimate in the same unit.

Your entries stay in this browser session. Download or copy anything you want to keep.

Formula or structure

Expected duration = (optimistic + 4 × most likely + pessimistic) / 6; standard deviation = (pessimistic − optimistic) / 6

Method reference: PMI: Five keys to estimating

Worked example

Estimates of 2, 5 and 14 days produce a 6-day weighted estimate and a 2-day standard-deviation estimate.

How to use it

  1. Read the field descriptions and use one consistent set of units.
  2. Enter your own figures or select Load example to inspect a worked scenario.
  3. Review the result alongside the assumptions below.
  4. Copy or download the output, then assign the next action in your planning workflow.

Assumptions and interpretation

The three-point assumptions do not establish a delivery probability. Dependencies and correlated risks can change a project schedule.

Read the practical guide

Questions about this tool

Can I mix days and hours?
No. All three estimates must use the same unit, and optimistic ≤ most likely ≤ pessimistic.
How does the pert estimate calculator work?
PERT uses three duration estimates to make uncertainty explicit instead of relying on a single optimistic deadline.
Do I need an account to use this tool?
No. This tool is free to use in your browser without signing in. My First Task is optional if you want to manage the resulting work in a shared workspace.
Are my inputs uploaded or saved?
The tool processes inputs locally in the browser and does not upload them or store them in an account. Copy or download any results you want to keep before leaving the page.

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