Total float is not the same question as schedule risk

What a CPM report actually tells you

A critical path method (CPM) schedule, correctly logic-linked and resourced, gives you a single deterministic finish date and a total float figure for every activity. It is a snapshot: given these durations, in this sequence, with this calendar, here is when the programme finishes.

That snapshot is necessary. It is not sufficient on its own to answer the question a sponsor actually cares about: how confident should we be in that date?

Why a single date cannot carry that answer

Every duration in a CPM schedule is a point estimate — a single number standing in for a range of plausible outcomes. Ground conditions, weather windows, statutory consultee response times, design coordination: all vary, and all can extend a duration beyond its planned figure. A single-point schedule has no way to express that variability, so it reports one date with implied certainty it cannot actually justify.

Quantified schedule risk analysis (QSRA) replaces each critical duration with a distribution (typically three-point: minimum, most likely, maximum) and layers in discrete risk events — a consent that might be delayed, a survey that might need to be repeated — each with its own probability and schedule impact. Running that through Monte Carlo simulation produces a distribution of possible finish dates, not one.

What float means differently once you do this

In a deterministic schedule, float is a fixed number computed once. In a QSRA model, the criticality index — how often an activity sits on the critical path across thousands of simulation iterations — becomes the more useful measure. An activity with modest deterministic float can still be highly critical in the probabilistic sense if its duration uncertainty is wide enough to regularly consume that float.

This is the practical payoff: QSRA does not just move the finish date, it re-ranks which activities actually deserve schedule-risk management attention, which is frequently not the same list a static float report would suggest.

Reading the output

A QSRA distribution lets you state a finish date at a confidence level — P50, P80 — the same way QCRA lets you state a contingency at a confidence level. Reporting "P80 completion: March 2027" is a materially more defensible statement to a board than a single deterministic date carried forward from a CPM report that has not been stress-tested against its own uncertainty.