Which finish date can you put in the contract?
Adding the likely durations gives the schedule everyone wants to promise. Simulation gives the one that survives: a P80 finish date and the list of tasks that actually drive it.
Words on this sheet
- Predecessors: The tasks that have to finish before this one can start. Put their IDs here, separated by commas, and leave it blank when nothing has to come first.
- F statistic: The variation between the groups divided by the variation inside them.
Construction Intermediate Schedule Risk Pro engine
After you install, this is the model to open.
The P80 Construction Schedule
- In your spreadsheet, click the Sortia icon in the strip of icons down the right-hand edge. No strip? Click the arrow at the bottom-right to open it. You can also use Extensions, then Sortia, then Open Sortia.
- Click Start from a template and put that name in the search box.
- Pick the card with that name and click Load this template. It arrives on a new tab with real numbers already in it.
This one runs on a Pro engine, and every free install includes five full-quality runs on your own numbers, shared across all five Pro engines rather than five for each. After that, Pro is $199/year.
The answer
Five thousand simulated builds:
- P50 finish
- 157 days
- P80 finish
- 165 days
- P95 finish
- 172 days
- 165-day promise holds
- 79% of trials
A 165-day commitment holds in 79 trials of 100: that is what a P80 date means, and it is the date that belongs in the contract. The criticality table shows permits, excavation and foundations on the critical path in essentially every trial, so acceleration money spent anywhere else buys nothing.
The model
Permits to handover in eight tasks, each a three-point estimate in working days from the trade that owns it, with the network defined by a predecessors column.
| Tasks | 8, permits through handover |
| Durations | optimistic / likely / pessimistic |
| Finish distribution | simulated |
| Criticality per task | simulated |
Once it is in your sheet
- The model arrives with real numbers in it and runs as it stands, so you can press the button first and understand it second.
- Change the numbers to yours. The sheet marks which cells are inputs and which hold formulas, and most labels carry a note explaining the row.
- Press the run button at the bottom of the panel. It is labeled for the tool you are in, and the result lands on its own tab, with a written reading of it beside the figures.
Never used Google Sheets? Start here goes the whole way, in seven steps, and assumes nothing.
Next question
- What are the odds the rain costs you the date?Will the Weather Blow the Deadline?
- What is finishing on time actually worth?What Do Late Days Really Cost?
- When does the punch list actually finish?Is Closeout on Track?
- What do the lean, normal and cautious bids each look like?Three Ways to Price This Bid
- Cheapest crew per site, or cheapest week?Which Crew Goes to Which Site?
- The rate says 90 a day. What do the site records say?What Does a Normal Crew Day Produce?
Every model like this one, and the method behind them: Schedule risk analysis.