Predecessor and Successor Tasks in Project Management

A project tracks green until one early task slips by two days, and then the finish date moves by two days or more, though nobody touched the later tasks. The links between tasks did that, and the two words for the ends of a link are predecessor and successor.

The direct answer: a predecessor is the task whose start or finish drives another task. A successor is the task that is driven. If testing cannot start until the build finishes, the build is the predecessor and testing is the successor. Scheduling software moves every successor automatically when a predecessor changes, which is why a wrong link is more dangerous than a wrong date.

In short. A predecessor drives; a successor follows. The link type (finish-to-start, start-to-start, finish-to-finish or start-to-finish) says which dates are tied, and lag adds a fixed wait. In Onplana's audit of 500 real Microsoft Project schedules in 2026, 83% had dangling tasks: work with neither a predecessor nor a successor, so nothing moves it when the plan changes.

The diagram below shows five tasks with their links, using working-day numbers where day 1 is the first day of the project.

What is the difference between a predecessor and a successor?

The difference is direction. The predecessor sits upstream and sets a constraint; the successor sits downstream and receives it. In the diagram, Build is the successor of Design and the predecessor of Docs and Test. Most tasks are both, and a task with neither is a dangling task.

How do the four link types change a successor's dates?

The link type picks which date of the predecessor drives which date of the successor. Finish-to-start is the default: the successor starts after the predecessor finishes. Start-to-start lets the successor begin once the predecessor has begun, finish-to-finish ties the two finish dates, and start-to-finish is rare. The four dependency types post covers each in depth. Lag adds a fixed wait to any of them; lead versus lag explains the negative case.

In the example, Docs starts two days after Build starts (start-to-start with 2 days of lag), so Docs runs on days 8 to 12 while Build is still going. Test is finish-to-start with a 2-day lag, so after Build ends on day 15, two days pass and Test starts on day 18. Counting is inclusive, so a one-day task starts and finishes on the same day.

What happens when a predecessor slips?

A slip travels down every path that depends on it. Suppose Design takes seven days instead of five. Build moves to days 8 to 17, Docs to days 10 to 14, and Test to days 20 to 23, so Release moves from the end of day 21 to the end of day 23. Docs has float because it finishes well before Test, so its move does not change the finish; Test is on the longest path, so its move does. That longest path is the critical path.

To work out what a change will touch:

1. Select the task that changed and list its successors.
2. Follow each successor to its own successors until you reach a milestone.
3. Mark the path that ends latest; that path sets the finish date.
4. Check each task on it for a link type or lag you did not intend.

How do you set predecessors and successors in a schedule tool?

In Onplana, you add a predecessor to a task on the Gantt by dragging a link or by picking it in the task, choosing one of the four types, and entering lag. Dependencies and lag are available on every plan, including Free, according to the plan matrix on the pricing page. The task dependencies page covers the commercial side; an imported plan keeps its links, as import without losing dependencies describes.

Before you share any plan, run the free Schedule Health Check on the file; it flags tasks with a missing predecessor or successor. For desktop work on a plan you keep editing, see Onplana Schedule.

Run the free Schedule Health Check Upload a project file and see which tasks have no predecessor or successor before your next review. No signup required. → Open the Schedule Health Check