What happens when a task is delayed?
A delay moves every task that depends on the late one, directly or through a chain, unless slack in the plan absorbs it first. A task on the critical path has no slack, so its delay reaches the finish date day for day. A task with float can slip by that much before anything after it moves; the rest of the delay passes on.
The example the simulator opens with shows both halves. Data migration trial loads has 10 days of float, because User acceptance testing also waits for System integration testing, which finishes later. A 14-day delay uses those 10 days, and the remaining 4 move Go-live from Dec 19, 2026 to Dec 23, 2026. Along the way 4 other tasks move, and the critical path changes: 9 tasks were critical before the delay, 8 after it.
How a delay travels through each dependency type
In the simulator, as in most real slips, a delay makes a task finish later; it still started on time. Which tasks that pushes depends on how they are linked:
| Link | The rule | A late finish on the first task |
|---|---|---|
| Finish-to-start (FS) | The second task starts after the first finishes | Pushes the second task, start and finish |
| Start-to-start (SS) | The second task starts after the first starts | Does not move it: only a late start would |
| Finish-to-finish (FF) | The second task finishes after the first finishes | Pushes the second task's finish |
| Start-to-finish (SF) | The second task finishes after the first starts | Does not move it: only a late start would |
A lag adds waiting time to a link (3SS+2: start two days after task 3 starts) and a lead overlaps the tasks (2-1). In the example, Integration build starts five days after Solution design starts, so it runs alongside Configuration build with 10 days of float. The guide to the four dependency types covers when each one fits.
Float, slack and the critical path
Total float is how many days a task can slip before the finish date moves. The tasks with none form the critical path, drawn in blue in the simulator. The engine recalculates float after every change, which is why a delay can put tasks on the critical path that were not there before.
The simulator reports the slack a delay actually used. It can be more than a task's total float when the task's start is tied to another task by a start-to-start link: the start is then critical while the finish still has room. The guide to total and free float and the critical path method explain the arithmetic.
How to use the simulator
- Start from an example or a blank plan, or paste rows from Excel, Google Sheets or Microsoft Project: a task name, a duration and the predecessors.
- In Depends on, write the rows a task waits for: 2 for finish-to-start, 3SS+2, 4FF or 5SF for the others. A duration of 0 makes a milestone.
- Choose the task that is late and by how many days. Tick Weekdays only to count working days, Monday to Friday.
- Read the result: the sentence, the tasks that moved, the new finish date and where the days could be won back. The task-by-task table lists every date, shift and float.
- Copy the link to share the plan. The plan is inside the link; nothing is saved on a server.
Common mistakes when judging a delay
- Assuming a delay moves the finish day for day. It does on the critical path. Anywhere else, float takes the first days.
- Looking only at the next task. A delay travels down every chain below the late task, and a merge point can hide it or pass it on.
- Treating every link as finish-to-start. Start-to-start and finish-to-finish links react to different ends of a task.
- Spending the same float twice. Tasks in one chain share its float: two delays on the same path draw on the same days.
- Counting calendar days on a working-day plan. Five working days is a full calendar week.
Questions
Is the delay simulator free?
Yes, with no account. A plan can have up to 30 tasks.
Is my plan stored anywhere?
No. The plan stays in your browser. A copied link carries the plan after the # sign, which browsers do not send to a server, and the page removes it from the address bar once it has read it.
Does it count weekends?
Only when Weekdays only is ticked: durations, lags, delays and shifts then count Monday to Friday. Public holidays are not modelled here; a Depentra project can name them in its working calendar.
Can I import a plan from Microsoft Project or Excel?
Copy the task name, duration and predecessors columns and paste them. ID columns, durations written as "5 days" and predecessors like 3FS+2 are understood, and start and finish dates work in place of a duration.
Is this the same engine as Depentra?
Yes. The simulator runs Depentra's scheduling engine, the one behind the Gantt, the critical path and the What-If simulator in the app.