Free Tool

PERT Calculator (Three-Point Estimate)

Compute the PERT expected value and confidence ranges from your optimistic, most likely, and pessimistic estimates. A fast, weighted three-point estimate for any task or project.

From a quick estimate to a real decision

PERT gives you a single weighted estimate and a standard deviation for one task. That is genuinely useful - but it assumes a tidy, symmetric spread and treats the task in isolation. Real projects have dozens of tasks whose risks pile up and interact.

The natural next step is a Monte Carlo simulation, which samples the full range thousands of times. Incertive does this across your entire plan and returns a probability of hitting your deadline or budget, not just a point estimate.

AI can describe your risk. Incertive calculates it.

This calculator gives you one estimate. Incertive runs thousands of Monte Carlo scenarios on your actual plan - success probability, sensitivity analysis, and a Go/No-Go you can defend, reproducibly, the same way every time.

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Frequently asked questions

What is the PERT estimate formula?

PERT (Program Evaluation and Review Technique) computes the expected value as (Optimistic + 4 x Most Likely + Pessimistic) / 6. The 4x weight on the most likely value makes it a weighted average that leans toward the realistic case while still accounting for both extremes. The standard deviation is (Pessimistic - Optimistic) / 6.

How is PERT different from a simple three-point average?

A simple average is (O + M + P) / 3, which treats all three points equally. PERT weights the most likely value four times as heavily, producing a more realistic estimate that is less swung by an extreme optimistic or pessimistic figure. PERT also gives you a standard deviation, so you can state confidence ranges, not just a single number.

What do the confidence ranges mean?

Assuming a roughly normal distribution around the PERT estimate, about 68% of outcomes fall within one standard deviation (Estimate +/- 1 SD) and about 95% within two (Estimate +/- 2 SD). So the +/- 2 SD range is a reasonable "almost certainly between" band you can commit to.

When should I use PERT versus Monte Carlo?

PERT is a fast, single-task estimate with a clean formula. Use it for a quick read on one activity. When a project has many tasks whose risks interact, a Monte Carlo simulation samples the whole model thousands of times and shows the true distribution - use our Monte Carlo calculator or Incertive for that.

Can AI give me a PERT estimate?

AI can recite the formula, but it will not consistently apply it to your numbers, and it returns a different answer each time. This calculator computes it exactly and shows the confidence ranges. Incertive goes further, turning three-point estimates across your whole plan into a probability of hitting your deadline or budget.

Related: Monte Carlo Calculator, Monte Carlo simulation, all calculators.