What finish date can you actually commit to?
A plan totals up to one number and offers nothing behind it. But every task on it is an estimate, and along a chain of dependencies the slow ones do not cancel out the fast ones. Simulating the same network turns your single date into a confidence ladder, so you can put a date in the minutes and say how often it holds.
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.
Work Advanced Schedule Risk Pro engine
After you install, this is the model to open.
What Finish Date Can I Commit To?
- 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
Add the longest chain of Likely durations by hand and the plan comes to 96 days. Ten thousand simulated runs of the same network say this:
- Plan on paper
- 96 working days, likely durations
- P50 finish
- 104 days, the coin flip date
- P80 finish
- 109 days, the date you can commit to
- What drives it
- 75% of runs driven by data migration
The 96-day plan is beaten in fewer than one run in ten, so it was never a commitment, it was a best case. The date you can hold eight times out of ten is 109 working days, and the 13-day gap between the two is schedule contingency you should be holding openly rather than hiding inside individual tasks. The criticality column then tells you where to spend attention: data migration drives the finish in 75% of runs against 25% for the interface build, while business readiness never drives it once. That is three activities to protect and one to stop chasing in status meetings.
The model
Fourteen activities of an enterprise system cutover, in working days, with optimistic, likely and pessimistic estimates on each. Two workstreams run in parallel after the requirements freeze and converge on integration test, then UAT, cutover rehearsal and go-live.
| Mobilise and baseline plan | 4 - 5 - 8 days, first activity |
| Requirements freeze | 6 - 8 - 14 days |
| Data migration workstream | profiling, scripts, trial load: 29 - 40 - 68 days |
| Interface workstream | specs, build, unit test: 25 - 37 - 61 days |
| Integration test | 12 - 16 - 26 days, waits on both |
| Defect fix, UAT, rehearsal | 17 - 24 - 43 days |
| Go-live and hypercare | 2 - 3 - 5 days, last activity |
| Simulation | 10,000 trials, PERT, seed 7 |
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
- How much buffer does this plan actually need?How Much Buffer Does This Plan Need?
- Should you certify this payment application?Should I Certify This Payment Application?
- Is the startup equity worth the pay cut?
- Two reps closed the same number. Who ranks first?Rank the Leaderboard, Ties and All
- Is there a typo dragging your average up?Catch the Outlier Entry
- One group is wild, one is steady. Is the gap real?Manual vs Automated, Tested Fairly
Every model like this one, and the method behind them: Schedule risk analysis.