Did that delay actually push the finish date?

An extension claim rests on one question, and it is not how late the activity ran. It is whether that activity was ever driving the finish, or whether another path was going to consume the time anyway. Criticality tells you which, and a second run tells you how much. What comes out is schedule evidence, not a legal opinion.

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.

Legal Advanced Schedule Risk Pro engine

Install free (opens the Google Workspace Marketplace in a new tab) How schedule risk analysis works

After you install, this is the model to open.

Did That Delay Actually Push the Finish Date?

  1. 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.
  2. Click Start from a template and put that name in the search box.
  3. 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

Run one is the as-built table. Run two changes one thing, C back to its planned estimates, and nothing else. Both runs share a fixed seed, so the whole difference is the activity you changed rather than sampling noise:

Criticality of C
96% of trials, as-built
P80 as-built
109.5 working days
P80 as-planned
99.5 working days
Extension supported
10 days, against a claim of 40

The disputed activity was on the driving path in 96% of trials, so the claim cannot be dismissed by saying it had float. But the two P80 figures differ by only about 10 working days against a claim of eight weeks, and the reason is visible in run two: with C back at its planned duration, the mechanical and electrical path takes over as the driver, jumping from 4% criticality to 99%. Most of the overrun was absorbed by float another path was going to consume anyway. Read criticality as what it is, the share of simulated runs in which an activity sat on the driving path, and take the result to your commercial lead rather than treating it as a determination.

The model

Twelve as-built activities of a fit-out package, in working days. Task C is the disputed one, where late access to level 3 ran to 28 days against a planned 10. Task E, the mechanical and electrical first fix, is a competing near-critical path.

Site setup and strip out11 - 14 - 21 days
C: late access to level 3 (disputed)20 - 28 - 40 days as-built
C: as-planned duration8 - 10 - 14 days
D: partitions and ceiling grid12 - 15 - 22 days, follows C
E: M&E first fix (competing path)27 - 34 - 46 days
M&E second fix, finishes, flooring24 - 33 - 49 days
Commissioning, snagging, handover14 - 20 - 32 days
Simulation20,000 trials, PERT, seed 7, both runs

Once it is in your sheet

  1. The model arrives with real numbers in it and runs as it stands, so you can press the button first and understand it second.
  2. 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.
  3. 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.

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Every model like this one, and the method behind them: Schedule risk analysis.

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