Project Timeline Calculator
Stacking Tasks Into a Real Finish Date
A project plan is only as trustworthy as the arithmetic behind it. Most timeline slippage doesn't come from one dramatic failure — it comes from a dozen small task durations that were never actually added up against a calendar. This calculator takes a list of task durations, in days or weeks, and turns it into a single total and, if you give it a start date, an actual projected finish date.
The Formula
The underlying logic treats the listed durations as a sequential chain:
When a start date is supplied, the end date is simply the start date plus the total duration in days (durations entered in weeks are converted at 7 days per week before adding).
Where This Is Useful
- Quoting a delivery date — convert a rough task breakdown into a defensible finish date before you commit to a client or stakeholder.
- Sanity-checking a plan — if the summed duration is longer than the deadline everyone has already agreed to, that's worth catching now, not in week six.
- Comparing planning units — teams that estimate in weeks and teams that estimate in days can be reconciled onto the same number.
Worked Example
Five tasks are estimated at 5, 3, 8, 2, and 6 days, starting on August 3, 2026:
| Task durations (days) | Number of tasks | Total timeline | Start date | Estimated end date |
|---|---|---|---|---|
| 5, 3, 8, 2, 6 | 5 | 24 days | 2026-08-03 | 2026-08-27 |
Durations are treated as fully sequential (no overlap). For plans where tasks run in parallel, use the Critical Path Calculator instead, which finds the longest chain among several concurrent paths.
How to Use This Calculator
- Enter Task Durations as a comma-separated list (for example,
5,3,8,2). - Choose the Duration Unit — Days or Weeks.
- Optionally enter a Start Date to get a projected end date along with the total.
- Select Calculate to see the total timeline and, if a start date was given, the exact end date.
Related Calculations
For projects with parallel workstreams, see the Critical Path Calculator. To lay individual task dates out day by day, use the Gantt Chart Duration Calculator.