Link Activities: FS, SS, FF, SF and Lag

Dependencies drive the critical path. schedule.construction supports all four relationship types (finish-to-start, start-to-start, finish-to-finish, and start-to-finish) with lag in working days.

Type in the Preds column

The fastest way when you know the IDs. Enter predecessors separated by commas:

The reference can be an activity ID, a WBS code, or a row number, tried in that order. If it can't be matched, you'll get an alert and nothing changes.

Draw link

Click Draw link in the toolbar, click the predecessor bar, then the successor bar. This always creates finish-to-start with no lag. Esc cancels.

Drag between bar connectors

Each bar has an S (start) and F (finish) connector. Drag from one to another, or click two in turn. The type comes from which ends you connect: F to S makes FS, S to S makes SS, F to F makes FF, and S to F makes SF. A review dialog shows the link before it's saved.

The Link activities dialog

Click Link activities, then choose the Predecessor, Successor, Relationship, and Lag (working days). Click Preview impact to see the effect on the finish date before you click Create link.

Edit or delete a link

Click a link line on the Gantt. The "Dependency A → B" panel lets you change the Type and Lag (days), then Save, or Delete link.

Rules

• No loops. A link that would create a cycle is refused: "This dependency would create a cycle. Choose a different relationship."
• No duplicates. Two activities can only have one link between them.
• Leads (negative lag) are allowed, but schedule validation flags them, and so do most owner specs. A lead usually means the activities should be split or linked start-to-start instead.

Which type to use

Most of a schedule should be finish-to-start. The DCMA quality check expects at least 90%. SS and FF with lag are useful for overlapping work like pulling wire behind conduit. SF is rarely right and is flagged by validation. For the theory, see the blog's relationship types guide.