From risk register to P80: schedule risk you can defend

1. A register that lives with the programme

Most risk registers die as standalone spreadsheets: unowned, unlinked to activities and never closed. A register earns its keep when each risk is tied to the programme activities it threatens, carries an owner and a response, and states its reasoning — why this risk, on this project, at this probability.

The contract and the programme are the best sources for the initial population: employer dependencies, design interfaces, weather-exposed activities, procurement long-leads, and the obligations your Particular Conditions tightened.

2. Set probability and impact honestly

Quantified risk is only as good as its inputs. Use ranges you can justify (three-point estimates from comparable work beat single-figure guesses), record the basis, and resist the workshop tendency to score everything medium. A register where every risk is 3×3 carries no information.

Review scores when the programme updates: a risk on an activity that has finished is closed, not carried.

3. What the S-curve actually tells you

Monte Carlo simulation runs the network thousands of times against the duration uncertainty and the mapped risks, producing a distribution of completion dates. P50 is a coin flip; P80 means eight runs in ten finish by that date. The gap between the deterministic finish and the P80 is the schedule contingency conversation — with the board, with the client, and in tender review.

Treat the output as a confidence statement conditional on the inputs, and say so when you present it. A P80 quoted without its assumptions invites the cross-examination it cannot survive.

4. The tornado tells you where to act

The tornado chart ranks which activities and which risks drive the spread of outcomes. That ranking is the mitigation agenda: effort spent on the top three bars moves the P80; effort below the waterline is risk theatre. Re-run after mitigation actions are agreed and compare the curves — the distance between pre- and post-mitigation distributions is the value of the mitigation plan, in days.