Project Toolkitby Maxime Lab
Schedule · tool 4 of 7

Schedule · tool 4 of 7

Dependencies, Leads and Lags

Dependencies, Leads and Lags: sets the true order of the work.

Best for: Building the schedule · Time: 1–2 hours
Domain: Schedule · Focus area: Planning

How it works

Tasks link in four ways: finish-to-start, start-to-start, finish-to-finish and start-to-finish. A lead lets a task begin early; a lag forces a wait. Most links are finish-to-start.

  • Mandatory dependencies come from the nature of the work.
  • Discretionary ones are a choice and can be changed.
  • External ones depend on people outside the project.

How to apply it

  1. List tasks with the people who’ll do them.
  2. Ask what must finish before each can start.
  3. Check that every task has a predecessor and a successor, apart from the first and last.
  4. Add leads and lags only for a real reason.
In practice

Plaster must finish before paint can start, plus a three-day lag for drying.

Pro tip

Track external dependencies by name and date. They cause the delays you can’t fix yourself.

Quick check

Paint must wait three days after plaster finishes. What is that?

Sources

  • PMBOK® Guide, 8th edition, and The Standard for Project Management (PMI, 2025)

Last reviewed 2026-11-02 against the PMBOK® Guide, 8th edition · Practitioner review pending · How this guide is made