How much buffer does this plan actually need?
Ask six leads for estimates and you get six numbers with padding quietly built into each one. That padding gets spent whether it is needed or not, because it belongs to nobody. Critical chain planning takes it back: aggressive durations on the tasks, and the safety pooled into one buffer you can watch burn.
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 Critical Chain Pro engine
After you install, this is the model to open.
How Much Buffer Does This Plan Need?
- 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
The safe estimates total 117 days against 72 days of focused work, so 45 days of padding are scattered across ten tasks. One click pulls it into the open:
- Critical chain
- 49 days on focused durations
- Project buffer (RSEM)
- 11.5 days, pooled from the safety given up
- Commitment
- 60.5 days, chain plus buffer
- Same buffer, 50% rule
- 24.5 days, sized from chain length
The padded estimates implied 117 days. The critical chain is 49, and RSEM sizes the project buffer at 11.5 days, so the commitment is 60.5 days with the safety in one place you can watch instead of scattered where it disappears. Two feeding paths get their own buffers, 8 days into migration wave 1 and 5 days into the cutover. The 50% rule sizes the same project buffer at 24.5 days because it works from chain length rather than from the safety each task gave up, though it is not a universal rule: on the single-task feeding path the order flips. One honest limit, worth knowing before you use it: the engine finds the chain as the longest path on focused durations and does not level resources, so if one team is committed to two paths at once, that judgment stays with you.
The model
Ten activities of a data center migration, in working days, with two durations on each. Focused is the fifty-fifty estimate, what the task takes when nothing goes wrong. Safe is the padded number the lead first gave you.
| Discovery and asset inventory | 8 focused / 13 safe |
| Target rack and power design | 6 / 10 |
| Network build and circuits | 12 / 20 |
| Storage array build and replication | 13 / 20 |
| Dependency mapping and rehearsal | 11 / 18 |
| Migration wave 1 | 9 / 14 |
| Cutover of core platform | 5 / 9 |
| Regression test and handback | 8 / 13 |
| Buffer sizing method | RSEM, with the 50% rule one click away |
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
- 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
- When the level shifts, how fast does your forecast follow?A Forecast That Trusts Recent Weeks
Every model like this one, and the method behind them: Critical chain planning.