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Intermediate

What is a dependency

Also known as: dependencies, task dependency, project dependency

Definition

A task dependency in project management is a link where one task cannot start or finish until another does. It sets the order of work and carries delays.

Why it matters

A dependency is what carries a delay from one task to the next.

Common mistakes

Assuming every link is finish to start, when some tasks can start together or overlap.

Related terms

Worked exampleIllustration

The design approval comes late

On the six week flower shop website, development cannot start until the design is approved, a finish to start dependency.

  1. The design approval comes 3 days late.

    +3 days

  2. Development starts 3 days late, because it waits on the approval.

    +3 days

  3. Testing and the launch move by the same 3 days.

    +3 days

  4. The shop's texts, written alongside, do not move, because nothing waits on them yet.

    0 days

The arrow is what carries the delay.

Illustration

One late approval, and everything that waits on it

Approved 3 working days late: development, testing and the launch all move by the same amount, into week 7. The texts stay where they were, because nothing waits on them yet.⁨Week⁩12345678⁨Texts (the shop)⁩⁨Design⁩⁨Development⁩⁨Testing⁩⁨Launch⁩+3

Approved 3 working days late: development, testing and the launch all move by the same amount, into week 7. The texts stay where they were, because nothing waits on them yet.

Each gold arrow is a finish to start link: the next task cannot begin until the one before it ends. Move the approval and follow the arrows.

Definition

PMI describes a dependency as a logical relationship between two activities. There are four types. Finish to start: B starts after A finishes, such as development after the design is approved. It is the most common type. Start to start: B can start once A has started. Finish to finish: B can finish only once A has finished. Start to finish: B can finish only once A has started, which is rare. Two more distinctions help. A mandatory dependency is hard logic that cannot be otherwise, while a discretionary one is a preferred order the team could change. An internal dependency sits inside the team, while an external one, such as a supplier's delivery, does not.

Why it matters

When a task that others wait on slips, everything behind it moves, while a task that nobody waits on can slip without effect. Knowing the links tells you which delays matter, who is waiting on whom, and which blockers (tasks that hold up other tasks) to clear first. Whether a slip moves the finish also depends on float: a task with spare days absorbs it, a task on the critical path does not.

Directly related: Project, Critical Path, Gantt Chart.

Improvement tips

  • For each task, ask what must be finished, or started, before it can go ahead.
  • Mark external dependencies, such as a supplier's delivery or a customer's approval, and agree their dates in writing.
  • Tell mandatory links from discretionary ones: a discretionary link can be changed to save time.
  • When a task is late, follow its arrows to see which tasks move with it and which do not.

Common mistakes

  • Leaving external dependencies off the plan, so the first sign of a supplier delay is the delay itself.
  • Treating a preferred order as unavoidable, and losing time that overlapping could save.
  • Updating a late task and forgetting the tasks that wait on it.

Related terms

Project ManagementBeginner

Project

A project is temporary work with a start and a finish that creates one unique result, such as a new website, within limits of scope, time and cost.

Project ManagementIntermediate

Critical Path

The critical path is the longest chain of dependent tasks in a project. It sets the finish date: a delay on it delays the project, a gain elsewhere does not.

Project ManagementBeginner

Gantt Chart

A Gantt chart is a schedule in which each task is a horizontal bar on a time scale, so you see what runs together, what waits and when the work ends.

OperationsBeginner

Bottleneck

A bottleneck is the slowest step in a process, the one that sets how much the whole business can deliver. In a small business, it is often the owner.

Quick check

Development waits for the design approval, and the approval is 3 days late. What happens to the texts the shop writes alongside, which nothing waits on?

Choose an answer

Frequently asked questions

Do I need to think about dependencies when starting my business?
Briefly, yes. Some launch tasks wait on others, for example a website cannot be built before its design is approved. Knowing the order stops you paying for work that cannot start yet.
When does a new business first run into task dependencies?
On the first plan with more than a few tasks. The moment one task waits on a supplier, a partner or another task, there is a dependency.
How do I map dependencies for my business launch?
List the tasks, and for each one ask what must happen first. Draw an arrow from that task to this one. The arrows show the order of work.
How does understanding dependencies save a new business money?
It stops you paying too early: booking a contractor, renting equipment or buying stock before the work they depend on is ready.
Why do dependencies matter for a business already running?
Hidden links cause waiting: people sit idle because the task they need is not done. Making the links visible shows where the waits come from.
What goes wrong when a business owner ignores task dependencies?
Work starts out of order and has to be redone, and one late task moves others that nobody connected to it.
How do I start tracking dependencies without stopping daily work?
Mark the blockers, tasks that hold up other tasks, in the list you already use, and review them first in the weekly meeting.
How do I manage dependencies that rely on outside suppliers?
Put the supplier's date in the plan as an external dependency, agree it in writing and confirm it before it arrives. If the date is shaky, plan what the team does in the meantime.
What does dependency mean in plain business words?
A link between two tasks: one cannot start or finish until the other does. You bake the cake before you decorate it.
Is tracking dependencies risky or complicated?
No. For a small project, arrows on a list or a board are enough. The work is asking what waits on what.
Do I need a project management expert to find dependencies?
No. A short meeting in which the team walks through the tasks in order usually finds them.
What happens if a task that many others depend on is delayed?
Every task behind it moves, unless the plan has spare days. Clear that blocker first, and check whether any waiting task can go ahead another way.

Sources: PMI, A Guide to the Project Management Body of Knowledge (PMBOK Guide), PMI, Lexicon of Project Management Terms

Last reviewed: 2026-09-24

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