P80 is the value with an 80% probability that the actual outcome will be at or below it. It is the most common confidence level for project budgets and committed dates, because it balances the cost of holding contingency against the cost of overrunning. Contingency is often set as P80 minus the base estimate.
S-curve. Illustrative QCRA result for a $120m base estimate. The highlighted point is the P80.
How P80 sets contingency
Contingency at P80 = P80 cost − base estimate
In the illustrative $120m example on the P90 page, the P80 is $133m. Contingency at P80 is therefore $13m, or 10.8%. The figure comes from the project's own risks, not from a rule of thumb.
Why P80 is the usual commitment level
P50 fails too often. Half of all outcomes miss it, which destroys credibility with sponsors and lenders.
P90 ties up too much capital. Across a portfolio, P90 budgets leave large sums unspent.
P80 is defensible. Many owners, funders and assurance reviewers expect P80 cost and schedule figures at sanction.
Schedule P80
For schedules, P80 is the date the project has an 80% chance of meeting. The gap between the deterministic Primavera P6 finish and the P80 date is the schedule contingency needed to commit to that date. In GCC brownfield work, shutdown and tie-in windows often drive most of this gap.
P80 cost and P80 schedule together
A P80 cost and a P80 schedule do not add up to an 80% chance of meeting both. The joint probability is lower, often nearer 65% to 70%, depending on how cost and time are linked. That is what a Joint Confidence Level analysis measures.
Common mistakes
Taking P80 from a model with no risk events. Ranges on activity durations alone understate the P80.
Spreading P80 contingency across every line item. Contingency belongs to the project as a whole; split it up and it gets spent.
Assuming P80 cost plus P80 schedule means 80% for both. It does not.
P80 is the value with an 80% chance the actual cost or finish date will be at or below it. Only one outcome in five exceeds it.
Why do projects budget at P80?
P80 balances the risk of overrunning against the cost of holding too much contingency. It is the level most sponsors, lenders and assurance reviewers expect at sanction.
How do you calculate contingency from P80?
Run a quantitative cost risk analysis, read the P80 from the S-curve, and subtract the base estimate. The difference is the contingency at 80% confidence.
Need a defensible P80 on a live project?
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