Split tasks in its minimum definition and estimate those minimum tasks by Optimistic (O) - Most Likely (M) - Pessimistic (P).
With those estimations we do PERT distribution and then add those estimations
(O+(4xM)+P)/6
Example
Task: Migrate x database Minimum tasks:
- migrate service 1 to y database
- migrate service 2 to y database
- migrate connector to use y database
- test changes in test env
Then we estimate those tasks
| task | Optimistic | Most likely | Pessimistic | PERT | Comments |
|---|---|---|---|---|---|
| migrate service 1 | 10h | 25h | 55h | 28h | (I round hours up) |
| migrate service 2 | 4h | 14h | 22h | 14h | take x into account |
| migrate connector | 20h | 40h | 80h | 44h | |
| test changes | 2h | 7h | 14h | 8h | |
| total estimation for task | 94h |
Reference(s)
https://www.knowledgehut.com/blog/project-management/three-point-estimating