Will we actually be ready when the guests arrive?

Prep starts at 1:00 PM, guests arrive at 6:00, and your task list adds up to 275 minutes, so the plan fits with 25 to spare. But every task on the list is a guess, and the slow guesses do not cancel out the fast ones when tasks wait on each other. Simulating the schedule tells you the real odds the doorbell beats the frosting.

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.

Life Intermediate Schedule Risk Pro engine

Install free How schedule risk analysis works

After you install, this is the model to open.

Finish Before the Party?

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

10,000 simulated party days, each sampling every task between its optimistic and pessimistic bounds and rolling delays through the dependency network:

Plan on paper: 5:35 PM 275 min of likely durations, 25 min spare
Chance ready by 6:00: 58% about 2 in 5 parties run late
Median simulated finish: 5:56 PM 1 in 10 runs end past 6:23 PM
What drives the risk: Cake chain critical in 68% of runs; dinner in 32%

On paper the schedule totals 275 minutes against a 300-minute deadline, a comfortable 5:35 PM finish. Simulated, the chance you are ready by 6:00 is only 58%: in roughly 2 of every 5 parties the guests arrive before the cake is decorated, because delays pile up along whichever chain runs slow. The bake, cool, decorate chain is the bottleneck in 68% of runs and the dinner in the rest, so shop first, get the oven on early, and stop worrying about the frosting and the cleanup, which almost never matter.

The model

Eight party prep tasks, each with optimistic, likely, and pessimistic minutes and finish-to-start dependencies: the cake must be baked, cooled, then decorated, while the dinner, cleanup, and frosting run in parallel.

Guests arrive (hard deadline)	6:00 PM, 300 min after the 1:00 PM start
Shop for ingredients & supplies	40 – 60 – 110 min, first task
Bake the cake layers	55 – 70 – 95 min, after shopping
Cool the cake layers	45 – 60 – 90 min, after baking
Make the frosting	20 – 30 – 50 min, parallel
Assemble & decorate the cake	45 – 60 – 110 min, after cooling & frosting
Clean & set up the party space	60 – 80 – 130 min, parallel
Cook the dinner spread	150 – 180 – 260 min, after shopping
Set the table & final walkthrough	15 – 25 – 40 min, last task

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.

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