Dependency types (FS, SS, FF, SF)

A dependency ties one task to another, so that moving the first moves the second. There are four types, named after which end of each task is tied: the start or the finish. Almost every plan uses the first one, finish-to-start, most of the time; the other three handle the overlaps real work has.

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The four types

Read each as "task B, which depends on task A":

Finish-to-start (FS): B starts when A finishes. Paint the walls, then hang the pictures. The default.
Start-to-start (SS): B starts when A starts. Write the report and start the charts for it on the same day.
Finish-to-finish (FF): B finishes when A finishes. Proofreading cannot finish before the writing does.
Start-to-finish (SF): B finishes when A starts. Rare: the old system runs until the new one starts.

Writing them in GanttCharts.app

The Depends on column takes the task it waits for, by number or name. A plain number is finish-to-start. Add the type after it for the others, and a lag in working days if there is one: "3SS" starts with task 3, "7FF+2" finishes two working days after task 7 finishes. The schedule redraws as you type.

Common mistakes

Chaining everything finish-to-start when tasks really overlap, which makes the plan longer than it is
Typing a fixed start date on a task that should follow another, which stops it moving when the earlier task slips
A loop (A waits for B, B waits for A), which no schedule can satisfy

Using dependencies in a project plan

QueryChart's guide walks through dependencies in a full project plan, with an example.

Using dependencies in a Gantt chart (QueryChart guide)

Frequently asked questions

What is a finish-to-start dependency?

The most common link between two tasks: the second task cannot start until the first one finishes. It is the default in almost every Gantt chart tool.

Which dependency type should I use?

Finish-to-start unless the work genuinely overlaps. Use start-to-start for tasks that begin together, finish-to-finish for tasks that end together.

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