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Why you should use lead and lag when creating project dependencies

When managing complicated projects, you can help people believe in your plan by creating tasks and milestones that describe the way people work. When a task doesn’t reflect reality, people will view it as inaccurate or irrelevant. But when tasks help them visualize the flow of work and find their place in it, they will use the plan as a guide.

One way to capture the natural flow of work in your planning is to use lead and lag times when creating tasks that are dependent on each other.

These tools paint a better picture of the way work unfolds than deadlines alone. They illustrate how tasks often overlap and happen concurrently or are stopped by another task that hasn’t been completed. This all makes the critical path that Perfect Project’s automation engine builds for you – and its estimates of your project’s completion date – more accurate.

These tools are easy to use, once you understand them, because they think about work the same way you do.

Understanding Dependencies

Before you use lead and lag, it helps to understand the different types of dependencies.

Some tasks are naturally dependent on the completion of other tasks: You don’t leave the house before you have your pants on, tie your shoes till you put your feet in them, or put the car in reverse until you start it. Similarly, at work, you don’t begin building a product for a client until they approve your bid. These are all called finish-to-start dependencies. You finish one before you can start the other.

This is the most common type of dependency. But there are others.

In some cases, finishing a task is not the trigger for starting the next one. Sometimes, you start the second task at the same time as the first one. Or maybe you can’t finish the second task until the first is completed.

Let’s say, for example, you get in the car to drive to work. You start the engine, plot your route in the nav, hit play on an audiobook, and drive.

  • You can’t begin driving (or your book) until you start the car, making these start-to-start dependencies.

  • The navigation won’t be done plotting your route until you complete the drive so that is a finish-to-finish dependency.

  • You can’t finish your audiobook (not in the car, anyway) until you start the car and begin driving so that is a start-to-finish dependency.

Lead Time

Both lag and lead time are ways of describing tasks that can’t be done in a day – or an hour – and that are dependent, in some way, on another task. Use lead time to build padding – of days or weeks – in front of the day when a task needs to be completed and lag time to build padding after a task is completed and before the next one is due.

Let’s say, for example, you have a deadline to deliver a proposal to a prospective client. After the development team discusses the scope of the project with the client, you need to gather ideas, calculate costs, and make sure you have technical resources available to do the work.

Preparing the proposal will take about a week, even though it’s only six hours of actual work, because you have to wait for people to respond to your questions, write a draft, and submit it to the sales and development teams for feedback.

Since you can’t start working on the proposal until the client meeting is completed, this is a finish-to-start dependency. To be sure you have the proposal ready by the deadline, you add seven days of lead time before the proposal delivery deadline. This gives you a deadline for when the client meeting has to happen.

Or Lag Time

If you had different information, you could also use lag time to describe the same scenario.

Let’s say you don’t have a deadline for the completion of the proposal. You do know, though, when the meeting with the client is scheduled. Since you can’t begin work on the proposal until the client meeting is done, again this is a finish-to-start dependency. Creating the proposal will take a week. So, with the client meeting as the first task, you would set one week of lag time after the client meeting task before the second task – delivering the proposal – is due.

Use the tool that reflects your work

You can choose whichever tool – the type of dependency, lead time, and lag time – that best suits the work you are doing and the deadlines you need to meet.

If you know, say, that the client meeting will happen on a certain day and that the goal is to build the product as soon as possible, use lag time after that meeting to set a deadline for the proposal.

If the client is expecting a proposal on a certain date but the meeting is not set, anchor the task for proposal delivery to a date and build lead time in front of it. This way you can set expectations – for the teams and the client – about when the meeting must happen.

After you deliver the proposal, you will also add lag time after that task – a few days perhaps – to allow the client to review it before you schedule the task, “Client Approved Proposal.”

Because, after the client approves the proposal, the work can start, which makes the next step in the project – Begin Building the Client’s Product – dependent on the client’s approval. And, as we decided in the beginning, that’s a finish-to-start dependency.

Why lead and lag make better projects

Using lead and lag time helps you build projects based on the way work unfolds, rather than attaching deadlines that aren’t realistic or accurate. These tools also help you calculate when dependent tasks need to happen.

When your plan is as nuanced as the work, people will be able to use it as a map to help them navigate through complex work. And that will help your company – and all the projects it takes on – stay on schedule and on budget.

Take an online tour of Perfect Project. Or book a demo and let us show you how our intelligent project management tools can keep your projects on track.



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