Project Timeline Calculator
Plan tasks with FS, SS, FF and SF dependencies and lag in working days; get the end date, slack, critical path, Gantt chart and CSV. How it works
Use the Project Timeline Calculator
About the Project Timeline Calculator
The project end comes from a forward pass over working days. The default plan, Task A (5 days), then Task B (10) and Task C (3), each starting after the one before, begins Monday, October 19, 2026 and ends Wednesday, November 11, 2026: 18 working days, 24 calendar days, with all three tasks on the critical path and 0 slack. Each task can depend on others by finish-to-start, start-to-start, finish-to-finish or start-to-finish links with a lag in working days.
The default plan, starting Monday, October 19, 2026
| Task | Duration | Start | End | Slack (working days) | Critical |
|---|---|---|---|---|---|
| Task A | 5 | Mon Oct 19, 2026 | Fri Oct 23, 2026 | 0 | Yes |
| Task B (after A) | 10 | Mon Oct 26, 2026 | Fri Nov 6, 2026 | 0 | Yes |
| Task C (after B) | 3 | Mon Nov 9, 2026 | Wed Nov 11, 2026 | 0 | Yes |
Five-day week. The project has 18 working days and 24 calendar days, and Task C ends on day 18.
How a link moves the second task: X lasts 5 days, Y lasts 3, both start from Monday, October 19, 2026
| Link from X to Y | Y starts | Y ends |
|---|---|---|
| Finish-to-start, lag 0 | Mon Oct 26, 2026 | Wed Oct 28, 2026 |
| Finish-to-start, lag 2 | Wed Oct 28, 2026 | Fri Oct 30, 2026 |
| Finish-to-start, lag −2 | Thu Oct 22, 2026 | Mon Oct 26, 2026 |
| Start-to-start, lag 0 | Mon Oct 19, 2026 | Wed Oct 21, 2026 |
| Start-to-start, lag 2 | Wed Oct 21, 2026 | Fri Oct 23, 2026 |
| Finish-to-finish, lag 0 | Wed Oct 21, 2026 | Fri Oct 23, 2026 |
| Finish-to-finish, lag 2 | Fri Oct 23, 2026 | Tue Oct 27, 2026 |
Lag counts working days; a negative lag is a lead. Work cannot start before the project start date.
Slack: Design (5 days) and Copy (2 days) both feed Launch (3 days)
| Task | Start | End | Slack (working days) | Critical |
|---|---|---|---|---|
| Design | Mon Oct 19, 2026 | Fri Oct 23, 2026 | 0 | Yes |
| Copy | Mon Oct 19, 2026 | Tue Oct 20, 2026 | 3 | No |
| Launch (after both) | Mon Oct 26, 2026 | Wed Oct 28, 2026 | 0 | Yes |
Copy can slip by 3 working days (to Fri Oct 23) before Launch is delayed.
How to use this tool
- Enter the project name and start date, and choose the working days per week (1 to 7, counted from Monday).
- Add tasks (up to 50) with a duration in working days, from 0.25 to 365 in steps of 0.25, or tick Milestone for a task with no duration.
- Link tasks: pick a predecessor, a type (FS, SS, FF or SF) and a lag from −30 to 30 working days.
- Read the end date, calendar and working days, the critical path, each task’s slack and the Gantt chart, then copy a share link or export a CSV. Tick Show all dates to add each task’s latest start and latest finish.
Frequently asked questions
- How do I find the critical path of a project?
- Read the Critical Path line above the Gantt chart, or the Critical column of the task table: in the default plan it is Task A → Task B → Task C. A day lost on any of those tasks moves the end date by a day. To finish sooner, shorten a critical task or let two of them overlap with a start-to-start link; shortening a task that has slack changes nothing.
- What is slack (float) and how is it counted here?
- Slack is how many working days a task can slip before the end date moves. In the Design, Copy and Launch example, Copy has 3 working days of slack: it can finish as late as Friday, October 23 instead of Tuesday, October 20. A task that slips by more than its slack becomes critical and pushes the end date out by the difference. Tick Show all dates to see the limits as dates: Copy’s latest start is Thursday, October 22 and its latest finish Friday, October 23.
- What do FS, SS, FF and SF mean?
- Finish-to-start (FS): the next task starts on the working day after the previous one finishes. Start-to-start (SS): it starts when the previous one starts. Finish-to-finish (FF): it finishes when the previous one finishes. Start-to-finish (SF): it finishes when the previous one starts. A lag in working days delays the link and a negative lag brings it forward.
- Why does the default plan take 18 working days but 24 calendar days?
- The tasks add up to 5 + 10 + 3 = 18 working days, and the calendar runs from Monday, October 19 to Wednesday, November 11, 2026. Those 24 days include 6 weekend days that carry no work. With a 7-day week the same plan ends on Thursday, November 5 after 18 calendar days.
- Can a task last a fraction of a day?
- Yes, in quarter days: the duration goes up in steps of 0.25 from 0.25 to 365. A 0.25-day task still occupies one working day on the calendar, so a plan with only that task shows 1 working day.
- Can I share or export the plan?
- Share Timeline copies a link that holds the project name, start date, working days and tasks, including names with commas. Export CSV writes the tasks with Duration (working days) and Slack (working days) columns, plus Latest start and Latest finish when Show all dates is ticked. Recent projects are listed in this browser.
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