Glossary
Schedule Risk Analysis (SRA)
A probabilistic analysis that models uncertainty in activity durations and discrete schedule risks to produce a range of possible project completion dates.
Schedule Risk Analysis (SRA) takes a deterministic programme and adds uncertainty to it. Rather than assuming each activity will take exactly its planned duration, an SRA assigns a three-point estimate (minimum, most likely, maximum) to each activity. It then applies discrete risk events — specific risks from the risk register that, if they occur, would add time to the programme — and runs a Monte Carlo simulation across thousands of iterations. The output is a probability distribution of project completion dates, typically displayed as an S-curve.
SRA is most commonly used to assess the confidence level of a target completion date. If the P50 completion date from the SRA is significantly later than the baseline programme, this tells the team that the baseline is optimistic and that contingency time needs to be added. SRA is also used to identify the activities and risks that most influence schedule outcome — the sensitivity analysis — so that the team can prioritise mitigation effort. On publicly funded infrastructure projects and defence contracts, SRA is frequently a requirement at stage gate reviews.
One of the most important and underappreciated outputs of an SRA is the gap between the deterministic end date and the P50 from the simulation. This gap exists even before any risks are switched on, because it reflects the effect of duration uncertainty and merge bias on the schedule network. If this gap is large, it usually signals that the schedule has too many parallel near-critical paths converging on the end milestone. A common mistake is running an SRA on a schedule that has not passed a basic quality check: poor logic, open ends, and excessive constraints will produce meaningless probabilistic output.
Frequently asked
- What is schedule risk analysis?
- Schedule Risk Analysis (SRA) is a probabilistic assessment of a project programme that models uncertainty in activity durations and discrete schedule risks. Rather than producing a single deterministic completion date, SRA runs a Monte Carlo simulation to generate a range of possible completion dates with associated probabilities — for example, a P50 date (50% confidence) and a P80 date (80% confidence). The gap between the baseline programme completion date and the P50 SRA date is the schedule confidence gap, which informs how much contingency time the programme needs.
- What is the difference between SRA and a risk register?
- A risk register identifies and qualitatively scores risks; an SRA quantifies their schedule impact. The risk register feeds the SRA: each risk event that could delay the programme is modelled with a probability of occurrence and a range of delay impact. The SRA also models duration uncertainty on individual activities independently of the discrete risk events. Together, the SRA tells you what the risk register costs in schedule terms — the register alone cannot do this.
- What does a P80 date mean in a schedule risk analysis?
- The P80 date is the completion date at the 80th percentile of the Monte Carlo output distribution — there is an 80% probability the project will complete by that date and a 20% probability it will run later. Many UK government frameworks and client organisations require SRA results to show the P50 and P80 dates, with funding allocated to at least P80 confidence. Programmes where the baseline completion date sits below the P50 SRA date are, by definition, more likely to overrun than not.
- What software is used for schedule risk analysis?
- The most widely used tools on UK infrastructure and defence programmes are Primavera Risk Analysis (formerly Pertmaster) for native P6 schedule integration, and Oracle Crystal Ball or Palisade @RISK for spreadsheet-based cost and schedule models. ARM (Active Risk Manager) is also used for integrated risk modelling. All tools use Monte Carlo simulation as the core engine; the differences are in how they handle schedule logic, correlation modelling, and output reporting.
Related terms
Putting these techniques into practice?
SOMA provides independent project controls consultancy for UK programmes. We can help you apply QRA, EVM, schedule risk analysis, and more.