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Project Dependencies with Lag/Lead Time

Delay the start of a task by adding lag or lead time to the dependency.

Most of the time, when two tasks are linked with dependencies in Microsoft Project, there is no lag. This article will show you how to add lead time to delay the start of a successor task after the predecessor task finishes.

This article focuses on how to add lag to dependency relationships between predecessor and successor tasks, and assumes that you already have knowledge of how to link tasks in Microsoft Project. We have an introductory article on Microsoft Project Predecessors, which is good to review before reading this article about lead time.

Adding Lag to Dependencies Using Keyboard Shortcuts

  1. Start with a simple Microsoft Project plan, which only has three tasks. Initially, both the second and third tasks, depend on the first task based on simple Finish-to-Start logic:
    Microsoft Project plan with three tasks.
  2. Let's assume that we want to add lag to the second dependency so that it doesn't start for seven days after the first task finishes. To do this, we'll click into the Predecessors field in Microsoft Project and change the dependency logic to read:

    1FS+7d

    In plain English, this means that the task depends on task "1" and is a Finish-to-Start ("FS") relationship, but is delayed by an additional seven days ("7d") of lead time.

    Add lag or lead time to a project dependency.

  3. Once you've typed in the new dependency logic, press ENTER, and Microsoft Project will recompute the start date of task #3 to reflect the delay:

    Task rescheduled in Microsoft Project due to lead time adjustment.

    Notice that task #2 and task #3 both depend on task #1, but task #3 starts later than task #2 because of the seven day lag in the dependency.

Review of Predecessor Syntax

When adding lead time to a predecessor, it's important to remember how your dependency syntax should be constructed:

[Predecessor ID Number] [Dependency Type] ([Operator] [Lag Time] [Lag Units])

The Predecessor ID Number is simply the line number of your Microsoft Project plan. So, if you want your task to depend on the first task in your project plan, simply enter a "1".

The Dependency Type can be one of four values:

  • FS: Finish-to-Start (If you leave the Dependency Type blank, Project will default to "FS")
  • SS: Start-to-Start
  • SF: Start-to-Finish
  • SS: Start-to-Start

If you don't need to add any lag, then your dependency can only consist of the Predecessor ID Number and the Dependency Type. If you do need to include lag, then you also need an Operator, plus the Lag Time and Lag Units.

The Operator is either a plus (+) or minus (-) sign, depending on whether you want to create positive or negative lead time. To delay the start of a task for a certain number of days after another task has finished, use a plus. On the other hand, if you want the successor task to start a few days before the predecessor finishes, use a minus.

Lag Time is simply the number of days, hours, weeks, etc. you want to compute in the lag.

Lag Units are the calendar units that reference the Lag Time. Lag Units can be one of the following:

  • d: Days
  • w: Weeks
  • mo: Months *
  • h: Hours
  • m: Minutes *

* Pay attention to minutes (m) vs. months (mo). If you get carried away and start typing too quickly, you can accidentally create a lag that is much shorter or longer than you meant.

Remember that lag is computed based on working time. So, seven days is not seven calendar days. Rather it is seven working days. The same is true for other Lag Units as well.

Adjusting Lead Time (Lag) in the Task Properties Window

Some users prefer a point-and-click approach to lead time adjustments instead of adjusting the lag formula. To do this:

  1. Double-click in the Predecessors cell that corresponds to the task whose lead time you want to adjust:

    Double-click on the predecessors column.

  2. When the Task Information pops up, click on the Predecessors tab review your existing lead times:

    Microsoft Project Task Information Screen

  3. In the Lag column, click the up and down controls to increase or decrease lag for a specific dependency:

    Increase or decrease the lag (lead time) for your dependencies.

Related Content

Microsoft Project Predecessors: Introductory Overview
Cross-Project Dependencies