Gantt Chart Duration Calculator
Every Bar on the Chart Needs an Exact Date
A Gantt chart is only useful when each bar has a real start and end date, not just a relative length. Given a project start date and a sequential list of task durations, this calculator walks through the chain and returns the exact start and end date for every task, plus the overall project finish — the same date math a scheduling tool does behind the scenes.
The Formula
Task End = Task Start + Duration
The first task starts on the project's start date; every task after that begins the instant the previous one ends, with no gaps and no overlap.
Where This Is Useful
- Building a chart by hand — get the exact per-task dates needed to plot bars, without opening dedicated scheduling software.
- Communicating a schedule — stakeholders respond to calendar dates ("Task 3 finishes August 19") far more reliably than to abstract day counts.
- Rebaselining after a slip — change the start date or a duration and immediately see how every downstream task date shifts.
Worked Example
Starting August 3, 2026, with four sequential tasks of 5, 3, 8, and 2 days:
| Task | Duration | Start | End |
|---|---|---|---|
| Task 1 | 5 days | 2026-08-03 | 2026-08-08 |
| Task 2 | 3 days | 2026-08-08 | 2026-08-11 |
| Task 3 | 8 days | 2026-08-11 | 2026-08-19 |
| Task 4 | 2 days | 2026-08-19 | 2026-08-21 |
Total project duration in this example is 18 days, from 2026-08-03 to 2026-08-21.
How to Use This Calculator
- Enter the Start Date for the project.
- Enter Task Durations in days as a comma-separated list, in the order the tasks run (for example,
5,3,8,2). - Select Calculate to see the start and end date of every task, plus the overall project end date and total duration.
Related Calculations
If several tasks can run in parallel rather than strictly in sequence, use the Critical Path Calculator to find the true driving chain, or get just the total length with the Project Timeline Calculator.