The schedule and the critical path
Once we know the work packages, we order them: what depends on what? You can't test the app before it's built, or build the ERP integration before designing the database. These are dependencies.
The critical path is the longest chain of dependent activities from start to finish, and it sets the shortest possible project duration. Any delay on the critical path delays the whole project. Other activities have float: days they can slip without moving the launch.
Here are the app project's activities. Change any duration and watch the critical path (in red) and the project length change:
| Activity | Days | Depends on | Starts day | Float |
|---|---|---|---|---|
| A Gather requirements | — | 0 | On the critical path | |
| B UI design | A | 5 | 3 | |
| C Database & API | A | 5 | On the critical path | |
| D Build the app | B | 11 | 3 | |
| E ERP integration | C | 15 | On the critical path | |
| F Test the app | D, E | 22 | On the critical path | |
| G Training & launch | F | 27 | On the critical path |
Critical path: A Gather requirements → C Database & API → E ERP integration → F Test the app → G Training & launch
Popular tools: Microsoft Project for detailed schedules, and Jira, Trello, Asana and Monday for agile teams. Excel is enough for small projects.