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Intermediate · 2 min read

Schedule risk analysis (Monte Carlo)

Replacing single-point durations with ranges to see the odds behind a finish date.

Working definition

A deterministic schedule prints one finish date computed from one set of assumed durations. A schedule risk analysis replaces those single points with ranges — optimistic, likely, pessimistic — and simulates the project thousands of times, sampling from the ranges each run. The output is not a date but a distribution: the probability of finishing by any given date. It is the difference between "we finish March 3rd" and "we finish by March 3rd four times out of ten."

Key takeaways

  • Three outputs matter.
  • The simulation is arithmetic; the ranges are opinions.
01

What the simulation produces

Three outputs matter. The P-values: P50 is the date with even odds, P80 the date with an 80% chance — and the gap between the deterministic date and P50 is a direct read on how optimistic the plan is. The criticality index: how often each activity lands on the critical path across runs, which surfaces near-critical paths a single calculation hides. And sensitivity: which activities’ uncertainty drives the finish, which is where management attention actually pays.

02

Where the honesty lives — and leaks

The simulation is arithmetic; the ranges are opinions. Ranges authored by the same optimism that built the schedule reproduce that optimism with a confidence interval around it. Ranges informed by history — how similar work actually ran — are where the method earns its keep. The other leak is correlation: durations in the real world move together (weather, labor markets, a struggling subcontractor), and treating them as independent narrows the distribution flatteringly.

Read honestly, a risk analysis is less a forecast than an audit of the plan’s buffers: a deterministic date sitting at P20 is not a plan with bad luck ahead of it — it is a commitment the network never supported. That is worth knowing before the date is promised, not after.

Sources and scope

Follow the reference trail.

This guide is original educational commentary. Kairos reference records identify the source organizations, editions and scope behind this guidance. The original publishers retain their publications and rights.

10S-90: Cost Engineering TerminologyAACE International · checked 2026-08-01Schedule Assessment Guide: Best Practices for Project SchedulesU.S. Government Accountability Office · checked 2026-08-01Recommended PracticesAACE International · checked 2026-08-01