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Slack time in project management: all you need to know

NitanshLast Updated: December 2, 2022

When it comes to project planning, we think it’s important because it helps us to execute the project better, right from ideation to completion. But planning also helps in keeping the variables in check so that there are not any last-minute surprises that could delay the project, or worse, lead to project failure. We have explained several such concepts such as project management crash or budget in project management. Today, we’ll be shedding light on another such aspect – slack time. Not to be confused with the popular communication app of the same name, slack time is an important factor that could help in ensuring that the projects are successfully executed. Read on to know why.

What is slack time?

Slack time is the maximum amount of time for delaying a task without delaying the project altogether. Since a project involves multiple tasks that are dependent upon each other, slack time ensures that the delay in any one of them (or more) can be easily managed. That’s because, a team member can finish their task early, and is waiting for the work to be finished by someone else to proceed further, or vice versa.

This also ensures that the project manager can get the tasks done by various stakeholders properly without affecting the project completion date.

How is slack time different from a float?

Technically, slack time is the same as a float. Both ensure that the project is a success while accounting for any unwanted delays.

The only difference is that slack time is usually used in the critical path method (CPM). Float on the other hand, is used primarily in project planning techniques like Scrum or work breakdown structure (WBS).

Read: Agile, Scrum, Waterfall, and More – top project management methodologies and how they’re different

What are the different types of slack time?

There are two types of slack time:

1. Free slack time – it’s the amount of time for which a task can be delayed without it starting to impact the next task.

2. Total slack time – it’s the amount of time a task can be delayed without letting it impact the project completion time.

Why is slack time crucial for project planning?

Project management - Flow

As you can intuitively understand that if the slack time isn’t considered, then the project won’t be finished in an efficient manner. Here’s why it matters:

1. Ensures that projects are on track: as a project manager, you are able to have a macro view of how the various tasks are being done so that the project gets successfully executed. One can also dedicate more resources if the tasks are taking more time, so that the timelines don’t get affected.

2. Better synchronization between the team members: Everyone in the team knows how much time they have to finish a task. So if they are taking more time to finish a task, they can highlight the fact that they will be able to finish without impacting the project deadline. Similarly, it will allow the other team members to focus on other tasks rather than being dependent on the first team.

3. Helps in prioritization: Since one can see the big picture, they can take a call if some task has to be prioritized as it’ll impact several other subsequent tasks. The opposite is true as well; low-priority tasks can be moved further below.

How to calculate slack time in project management?

Calculating slack time is quite easy. It’s the difference between the latest start time (LST) and the earliest start time (EST). As the naming convention indicates, LST refers to the last date for any task to begin without causing a delay, while EST is the first date when the task should start.


Another variation of the equation could be basis the finish time rather than the start time, i.e. the difference between the latest finish time (LFT) and earliest finish time (EFT).

To illustrate it further, we can take an example of a video series being planned for various team members which will be published on YouTube.

 Start timeFinish time
EarliestDay 11Day 30
LatestDay 17Day 37

In this case, the Slack Time will be 6, which you can calculate by either LST – EST or LFT – EFT.

By knowing the slack time, the project manager knows that there’s some time and a later start date will not impact the project deadline.

An example of slack time

Let’s consider an example of a project that will help us understand slack time better. Let’s consider that you are launching a revamped website just in time to coincide with the new version of your software. To successfully do it, here are the things that must happen on time:

1. Getting the copies written for various pages of the website

2. Getting the design done for all the pages of the website

3. Start HTMLising these pages

4. Ensure that the pages follow SEO guidelines and there are not any broken links

Of course, there could be several other granular things, but these are things that must be done correctly.

Use Flow to find the slack time!

While you can manually find slack time in project management, it could be a lot easier if you use a project management software like Flow. It gives you instant visibility of your resources in intra-team and cross-team project management, so you don’t miss out on any detail. To try it for free, register for a 30-days free trial today.

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