Wiggle Room Calculator
For background, see the original post. Use whatever estimation units you prefer – days, story points etc.
| Historical velocities (optional) | |||
|---|---|---|---|
| Historical Velocities | hv | (velocities achieved in recent iterations, comma-separated) | |
| Inputs | |||
| Planned iterations | ni | (planned iterations) | |
| Velocity | v | (estimation units achieved on average per iteration) | |
| Velocity variation (%) | vv | (standard deviation of velocity as percentage of velocity) | |
| Creep | rc | (estimation units added to backlog per iteration) | |
| Calculated | |||
| Effective velocity |
ev | v – rc | |
| Iteration length variation |
lv | (1/(1 – vv) – 1) * 100% | |
| Contingency iterations |
c | 2 * sqrt(ni) * lv | |
| Contingency work reserve |
cw | c * ev | |
| Planned work available |
pw | ni * ev – cw | |
The v and vv fields will be calculated from the historical velocities hv if these are provided.
Example: ni = 10 (iterations), v = 20 (story points per iteration), rc = 2 (story points per iteration), vv = 20 (percent) suggests those 10 iterations should include a contingency element of 1.5 iterations (or 27.8 story points at the effective velocity), allowing 152.2 story points of critical work to be attempted with 95% confidence.
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