Is the migration in trouble, or just early?

Eight tasks, thirty-seven days of padding hidden inside them, and one shared buffer to replace it. Then six status updates on a fever chart, where the same amount of buffer burn is a crisis at week six and healthy at week twelve.

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.
Project buffer: The shared pool of safety time placed at the end of a critical chain plan instead of padding inside each task.
F statistic: The variation between the groups divided by the variation inside them.

SaaS Advanced Critical Chain Pro engine

Install free How critical chain planning works

After you install, this is the model to open.

Buffer the Migration, Not the Tasks

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

Commit to: 60 days against the 88-day padded plan
Project buffer: 20 days half of the 40-day critical chain
RSEM sizing: 12.4 days a 52.4-day commitment, the leaner method here
Week 6: red 55% of the buffer gone at 30% of the chain
Week 12: green 62% spent with 88% complete

Eight tasks of a platform migration in working days, each with two numbers. Focused is the aggressive fifty-fifty estimate, what the task takes when nothing goes wrong and nobody is protecting themselves. Safe is what the same engineer wrote in the plan. The safe estimates total 88 days against 51 days of focused work, so 37 days of safety are scattered across eight tasks in places where they get consumed quietly and never handed back.

Click Run. The critical chain comes back as the schema freeze, the extract and transform build, the dry run, the reconciliation fixes, the rehearsal and the cutover weekend, 40 days long on focused durations, and with the 50% rule the project buffer is 20 days, so the commitment is 60 days rather than the 88 the padded plan implied. Two feeding paths join the chain and each gets its own buffer: customer comms feeds the cutover with a 2.5-day buffer, and the rollback tooling feeds the rehearsal with 3 days.

Switch the buffer sizing to RSEM and rerun to see the other shipped method. The project buffer becomes 12.4 days for a 52.4-day commitment, because RSEM sizes from the safety each task actually gave up rather than from the length of the chain, and on a chain this long that produces a leaner number. Neither method is simply the conservative one: on a short chain carrying enormous padding the ordering reverses, which is why the control exists rather than a default.

Now the fever chart, which is the half of critical chain that almost nobody sets up. It only appears when the run is given a status range, which is why this template ships one. The six updates report how much of the chain is done and how much of the buffer is gone, and the chart classifies each point against two sloping lines rather than against a fixed threshold.

Week 2 is green at 10% of the buffer for 12% of the chain. Week 4 is yellow. Week 6 is red: 55% of the buffer gone for 30% of the chain done, which is a project in real trouble. Weeks 8 and 10 are yellow as the chain catches up. Week 12 is green at 62% of the buffer for 88% of the chain, and only just green, which is worth seeing rather than smoothing over.

Read the last two facts against each other, because they are the entire idea. At week 6 the project had spent 55% of its protection and that was a crisis. At week 12 it has spent more, 62%, and it is healthy. Buffer consumption is only meaningful against progress, and the sloping zones say what a fixed percentage cannot: burning half your protection in the first third of the work is how projects die, and burning two thirds of it by the end is how they were always going to finish.

One thing to watch in the report. The trend reads worsening on this data, because buffer consumption only ever goes up, while the zone reads healthy. The zone is the one to act on. Two honest limitations. The chain is found as the longest path on focused durations and the tool does not level resources, so if the same two people are committed to the chain and to the rollback tooling at once you have to spot that yourself, and Resource Load on a version of this table with an Owner column will do it.

And a buffer only works if it is managed centrally: the moment a task is allowed to take a quiet slice of it, you are back to padding with extra steps. To adapt it, put your own tasks in, ask every lead for a focused and a safe number in the same conversation, and add one status update a week from your own stand-up rather than at the end.

The model

It arrives on a tab called Template: Migration Chain, carrying these columns:

ID
Task
Predecessors
Focused duration (days)
Safe duration (days)
Update
Chain complete (%)
Buffer consumed (%)

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

Every model like this one, and the method behind them: Critical chain planning.

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