Dependencies in Microsoft Project: FS, SS, FF and SF

Durations say how long the work takes. Dependencies say what has to happen first. In Microsoft Project, the links between tasks are what turn a list of dates into a schedule that moves when something slips. This lesson covers the four link types, finish-to-start (FS), start-to-start (SS), finish-to-finish (FF) and start-to-finish (SF), how to enter and edit them, and the logic rules an owner should insist on.

Learning outcomes

• Define predecessor and successor, and explain the four dependency types with a construction example of each.
• Create, change and remove links in Microsoft Project desktop using the ribbon, the Predecessors column and the Task Information dialog box.
• Read and write predecessor codes such as 8, 34SS and 31SF.
• Apply basic logic rules: link work rather than summary tasks, avoid open ends, and keep most links finish-to-start.

The lesson

Predecessors, successors and why links matter

A dependency (Project also calls it a task link) connects two tasks. The predecessor is the task that controls; the successor is the task that depends on it. Once tasks are linked and automatically scheduled, Project calculates the successor's dates from the predecessor's dates, the link type, any lag, and the calendar. Change a duration upstream and everything downstream moves. That is the whole point: a linked schedule tells you the consequence of a delay before anyone has to work it out by hand.

Links only drive automatically scheduled tasks. A manually scheduled task keeps the dates you typed even if its predecessor moves, which is one more reason the owner's master schedule runs in Auto Schedule mode (lesson 3, and lesson 10).

The four dependency types

Microsoft describes each type by what the dependent task (B) cannot do until something happens to the task it depends on (A). In plain terms:

• Finish-to-start (FS). B cannot start until A finishes. This is Project's default and the most natural way to describe construction: the permit is issued, then the site mobilizes.
• Start-to-start (SS). B cannot start until A starts. Useful when work overlaps: once commissioning starts, the owner's operations staff can start training on the commissioned systems.
• Finish-to-finish (FF). B cannot finish until A finishes. Useful when one task tracks another: the commissioning agent's witness testing cannot finish before commissioning itself finishes.
• Start-to-finish (SF). B cannot finish until A starts. The rarest type, and the one most often misused. A fair construction example is a handover between systems: the contractor's temporary power cannot be removed until permanent power starts.

Microsoft's own SF example is a roof assembled from trusses built off site: the assembly task cannot finish until truss delivery starts. Many schedulers find SF counter-intuitive because the arrow seems to point backward in time, and most SF links can be rewritten as an FS or FF link that reads more naturally. Reach for SF only when the successor's finish really is controlled by the predecessor's start.

How to link tasks in Project desktop

There are several ways to create links. Use whichever suits the moment, but check the result in the Predecessors column.

1. Ribbon. In the Gantt Chart view, select two or more tasks (hold Ctrl to pick tasks that are not next to each other), then choose Task > Link Tasks in the Schedule group. Project creates FS links in the order you selected the tasks. The keyboard shortcut is Ctrl+F2.
2. Predecessors column. Type the predecessor's ID number in the successor's Predecessors cell. A plain number means FS. Add the type code after the ID for anything else, and separate several predecessors with commas (Figure 3).
3. Task Information. Double-click a task, or choose Task > Information, and open the Predecessors tab. Each row shows the predecessor's ID and name, a Type list and a Lag box. This is the clearest place to review all of a task's logic at once.
4. Gantt or Network Diagram. Drag from one bar or box to another. Quick, but easy to do by accident; turn it into a habit to check the Predecessors column afterwards.

To change a link type, double-click the link line on the Gantt chart and pick a new type from the Type list, or edit the Type column on the Predecessors tab. To remove links, select tasks and choose Task > Unlink Tasks, which removes all links between the selected tasks; to remove one link only, delete that row on the Predecessors tab. Lags and leads, the waiting time on a link, have their own lesson next (lesson 8).

Screenshot to come

Logic rules worth enforcing

Project will accept almost any link you give it. Good logic takes discipline. Four rules catch most problems:

• Link work, not summaries. Project lets you link summary tasks, but the dates of a summary come from its subtasks, and links on both levels compete. The GAO Schedule Assessment Guide is blunt: "summary activities should never be linked to or from other activities." Link the detailed tasks and milestones instead.
• No open ends. Every task needs at least one predecessor and one successor, except the project start and finish milestones. A task with no successor can slip without moving anything, so the schedule will not show the delay.
• Watch the sides of SS and FF. A task with only an SS successor has nothing tied to its finish, and a task with only an FF predecessor has nothing tied to its start. Each side of a task should be driven by, and drive, something. Schedule reviewers call the gap "dangling logic".
• Mostly FS. The DCMA 14-point assessment, a common schedule-quality check, expects at least 90 percent of links to be finish-to-start. SS and FF links have their place; a schedule built mainly from them is usually hiding overlaps that should be split into smaller tasks.

A fifth rule belongs to a later lesson: do not replace a missing link with a typed date. Typing a start date on an auto-scheduled task creates a constraint, and constraints stop logic from working (lesson 12).

Northgate worked example

The owner's PM for Northgate Distribution Centre (fictional) now links the owner's master schedule, NDC_OwnerMaster_2027-01-11.mpp. The owner's file carries the contract milestones, the owner's own tasks and Halvorsen Builders Ltd.'s (fictional) key phases. Figure 2 shows the spine of the network from contract execution to Ready-for-Takeover, with the three non-FS links highlighted.

View the data

Predecessor	Successor	Type
M0 Contract executed (Mon 2027-01-11)	M2 Building permit issued (Fri 2027-02-26)	FS
M2 Building permit issued	M3 Site mobilization (Mon 2027-03-01)	FS
M3 Site mobilization	Foundations and slab (to M4 Fri 2027-05-14)	FS
Foundations and slab	Tilt-up panels (to M5 Fri 2027-06-25)	FS
Tilt-up panels	Roof and envelope (to M6 Fri 2027-09-03)	FS
Roof and envelope	M7 Permanent power (Fri 2027-10-01)	FS
M7 Permanent power	Temporary power (contractor)	SF
M7 Permanent power	Commissioning (starts M8 Mon 2027-11-01)	FS
Commissioning	Owner staff training	SS
Commissioning	CxA witness testing	FF
Commissioning, Owner staff training, CxA witness testing	M9 Ready-for-Takeover (Fri 2028-01-14)	FS

Three points from the diagram are worth drawing out.

• The FS spine carries the story. Permit, mobilization, slab, panels, roof, power and commissioning follow one another. In the owner's file these are summary-level phases; Halvorsen's P6 schedule holds the detail. The links still sit on tasks and milestones, never on the WBS summary rows from lesson 5.
• SS and FF are both tied off. Training starts once commissioning starts (SS), and it also has an FS successor, M9, so its finish drives something. Witness testing cannot finish before commissioning finishes (FF), and it also feeds M9. In the full file, training also has a start-side predecessor from the commissioning plan, so neither task dangles.
• The SF link is a handover. The owner does not schedule temporary power, but tying its finish to the start of permanent power shows that removing it early would be a problem. Some owners would model the same idea as an FS link from M7 to a "remove temporary power" task. Both are defensible; the FS version is easier for most readers to follow.

Figure 3 shows how the same links look in the Predecessors column. The ID numbers are illustrative; they will differ in your own file.

Before moving on, the PM runs two checks. First, a quick scan of the Predecessors and Successors columns (add Successors from the column picker) for any task other than M0 and the final milestone with a blank cell. Second, a count of link types: in this spine, 3 of 13 links are non-FS, which is fine for a short excerpt, but the full owner's file should land well above 90 percent FS.

Screenshot to come

Screenshot to come

Owner's move

• Ask for the logic, not just the dates. Require native schedule files (XER for Halvorsen's P6 schedule, MPP for any consultant schedule), so the links can be inspected. A PDF Gantt chart hides every dependency.
• Run three quick checks on every submission: open ends, links on summary tasks, and the share of FS links. Ask for a written explanation of every SF link.
• Put owner tasks in the network. Permit support, owner reviews, owner-supplied items and training belong in the logic with real links to the contractor's milestones, so their delays show up as delays.
• Challenge typed dates. If a contractor milestone moves only when someone retypes it, the schedule is not linked. Ask what drives it.

Logic is where a schedule earns its keep. The owner who reads the links, not just the bars, sees a slip weeks before it reaches a milestone.

Common mistakes

1. Linking summary tasks. It looks tidy and confuses the critical path. Link the work inside them.
2. Linking tasks in the wrong order. Link Tasks follows the order you selected them in. Click the predecessor first.
3. SS without a finish-side successor. The overlapping task can run on forever without affecting anything.
4. Using SF to mean "finish-to-start, backwards". If you have to explain the SF link twice, rewrite it as FS.
5. Unlink Tasks on a large selection. It removes every link between the selected tasks, not just the one you meant. Use the Predecessors tab for a single link.

Quick quiz

1. What link type does Project create by default when you choose Task > Link Tasks?

   1. Start-to-start
   2. Finish-to-start
   3. Finish-to-finish
   4. Start-to-finish

2. Owner staff training can begin once commissioning has begun. Which type fits?

   1. FS
   2. SS
   3. FF
   4. SF

3. What does 34FF in task 36's Predecessors cell mean?

   1. Task 36 cannot finish until task 34 finishes
   2. Task 34 cannot finish until task 36 finishes
   3. Task 36 cannot start until task 34 finishes
   4. Task 36 has 34 days of float

4. According to the GAO Schedule Assessment Guide, how should summary activities be linked?

   1. Only with FS links
   2. Only to milestones
   3. They should never be linked to or from other activities
   4. Only within the same WBS level

5. A schedule-quality check expects at least what share of links to be finish-to-start?

   1. 50 percent
   2. 75 percent
   3. 90 percent
   4. 100 percent

Show answers and explanations

1. B. Finish-to-start is Project's default. Change the type afterwards on the Predecessors tab or by double-clicking the link line.
2. B. Start-to-start: the successor's start depends on the predecessor's start.
3. A. The code sits on the successor (36) and names the predecessor (34) and the type: finish-to-finish.
4. C. Summary dates roll up from their subtasks; link the detailed tasks instead.
5. C. The DCMA 14-point assessment uses a 90 percent FS threshold.

Key terms

Dependency (task link)

A logical relationship that makes one task's dates depend on another's.

Predecessor

The task that controls in a dependency.

Successor

The task whose dates depend on the predecessor.

Finish-to-start (FS)

The successor cannot start until the predecessor finishes. Project's default.

Start-to-start (SS)

The successor cannot start until the predecessor starts.

Finish-to-finish (FF)

The successor cannot finish until the predecessor finishes.

Start-to-finish (SF)

The successor cannot finish until the predecessor starts. Rarely needed.

Open end (dangling logic)

A task missing a predecessor or successor, or with nothing tied to its start or its finish.

References

1. Microsoft Support, Link tasks in a project (dependency types, Link Tasks, Unlink Tasks, Predecessors tab).
2. U.S. Government Accountability Office, Schedule Assessment Guide: Best Practices for Project Schedules (GAO-16-89G), Best Practices 1 and 2.
3. GAO Innovations, Schedule guide: ten best practices.
4. Deltek Acumen help, DCMA 14-Point Assessment metric descriptions (relationship types, missing logic).
5. Steelray, DECM: summaries with logic.

Verified on November 4, 2026.

Next lesson in this trackLags and leads