The ultimate guide on how to calculate Slack time (2024)

Tips on how to calculate slack time
Table of contents
Get social

Follow us for the latest updates, productivity tips and much more.

What is Slack time

Consider “slack time” as the breathing space in your weekend agenda. Picture your non-negotiables—brunch, Netflix, a potential workout—as the critical tasks. Tweak those, and your weekend groove might suffer. Now, think of the open slots between these activities—that’s your slack time.

It’s not downtime; it’s your cushion. If brunch extends or the workout morphs into a nap, no problem. Slack time is your unscheduled hero, letting you handle surprises without chaos.

Now, shift this notion to the professional arena. Nailed a project, and the next one’s in a holding pattern? That’s not a productivity glitch; it’s your workday’s slack time. A chance to recharge, maybe enjoy guilt-free meme-scrolling before the next mission. Employers get it too—building intentional slack time into schedules keeps things not just smooth but dare I say, enjoyable in the daily hustle.

But all of this can be a bit confusing, so to ease your journey to knowing slack time, we created the ultimate guide to calculate slack time. Read on to know more!

Pro Tip: You can also use Tackle to calculate your team’s performance and productive time as well! That’s right, Tackle allows you to track, allocate, and analyze your time with ease. and help you achieve your goals like a boss!

What is critical path

The critical path stands as a cornerstone in project management, embodying the pivotal sequence of tasks. Akin to the main artery, any delay along this path directly influences the project’s overall completion time.

calculating slack time in project management

Determining the critical path involves meticulous examination of a network diagram, considering task dependencies and durations. Tasks aligned with the critical path leave no room for flexibility—they boast zero slack time. A delay in these tasks invariably extends the project’s finish date. It serves as the linchpin, providing project managers with a focused trajectory for successful project execution.

How to calculate Slack time

Now that you understand what is slack time, let’s dive in to know how to calculate slack time. Just to give a heads-up, the step by step procedure from here might be a little tricky to understand, but you got this!

calculating slack time critical path in Tackle

Here’s a step-by-step guide on how to calculate slack time:

📋 Determine task durations

  • Estimate the time each task will take to complete. This can be in days, weeks, or any relevant time unit.

🌐 Create a network diagram (as shown above)

  • List all the tasks or activities required for the project.
  • Identify dependencies between tasks. Some tasks may need to be completed before others can start.
  • Use the task list and dependencies to create a network diagram. Nodes represent tasks, and arrows represent dependencies.

🧮 Calculate early start (ES) and early finish (EF)

  • For each task, calculate the Early Start (ES) and Early Finish (EF):
    • ES: The earliest time a task can start based on its dependencies.
    • EF: The earliest time a task can finish, calculated by adding its duration to the Early Start.

🧮 Calculate late start (LS) and late finish (LF)

  • Determine Late Finish (LF) and Late Start (LS) for each task:
    • LF: The latest time a task can finish without delaying the project.
    • LS: The latest time a task can start without delaying the project.

⏰ Calculate Slack time (Total float)

Slack time, also known as float, is calculated in project management to determine the flexibility or leeway within a schedule.

How to calculate slack time network diagram

The formula for calculating slack time depends on whether you are considering the early start and early finish times or the late start and late finish times. Here’s how you can calculate slack time:

🧮 Using early start and early finish

  • Slack Time (Total Float) = Late Start – Early Start or Late Finish – Early Finish
  • Calculate the early start and early finish times for each activity on the critical path.
  • Calculate the late start and late finish times for each activity on the critical path.
  • Subtract the early start from the late start (or early finish from late finish) for each activity to find the slack time.

🧮 Using late start and late finish

  • Slack Time (Total Float) = Late Start – Early Start or Late Finish – Early Finish
  • Calculate the early start and early finish times for each activity on the critical path.
  • Calculate the late start and late finish times for each activity on the critical path.
  • Subtract the early start from the late start (or early finish from late finish) for each activity to find the slack time.

🧮 Individual activity Slack time

  • If you are interested in the slack time for a specific non-critical activity, you can calculate it using the formula:
  • Slack Time (Individual Activity) = Late Start – Early Start or Late Finish – Early Finish
  • Again, calculate the early start and early finish times for the specific activity.
  • Calculate the late start and late finish times for the specific activity.
  • Subtract the early start from the late start (or early finish from late finish) to find the slack time for that particular activity.
  • A positive slack time indicates how much a task can be delayed without delaying the project.

📊 Identify the critical path

  • The critical path is the sequence of tasks with zero slack time. It represents the longest path through the network.
  • You can see in the above diagram the critical path is from Task A, Task B, Task E, Task G and Task H. It takes the longest path to complete Task H.

✨ Interpret the results

how to calculate slack time
slack time calculator
  • Positive slack time indicates flexibility in the schedule, allowing for delays without impacting the project.
  • Zero slack time means the activity is on the critical path and cannot be delayed without affecting the project timeline.
  • Negative slack time suggests that the project may be at risk of delay if the activity is not completed on time.

🔥 Wrapping it up!

Nailing slack time is like having a cool sidekick in project management—it’s your flexibility buddy. Picture this: adjustments without the project chaos. Slack time, that unsung hero, works in personal plans and the work hustle, providing the space for unexpected twists.

Understanding it, along with buffer time and float, is your project ninja move. The critical path? Think of it as the project’s heartbeat, the VIP sequence. Calculating slack time on this path involves a bit of choreography, but once you get it, your project dances to success. So, let the rhythm of slack time guide you to project management stardom! 🚀

💡 Tackle pro tip
Since you read about on how to calculate slack time, you might be interested in the following:

🌟 Frequently asked questions

What is the formula for Slack Time?

Slack time, or Total Float, is calculated using the formula: Slack Time = Late Start – Early Start or Slack Time = Late Finish – Early Finish. It represents the flexibility within a schedule, allowing for adjustments without impacting project completion.

How is total Slack calculated?

Total Slack is calculated by determining the difference between the late start and early start times for each activity on the critical path. The formula is: Total Slack = Late Start – Early Start or Total Slack = Late Finish – Early Finish.

How do you calculate critical path and Slack time?

To calculate the critical path, create a network diagram, estimate task durations, identify dependencies, and then determine early start, early finish, late start, and late finish times for each task. The critical path consists of tasks with zero slack time. Slack time is calculated using the formula mentioned in the first two answers.

What is Slack time of a day?

Slack time is typically measured in days, weeks, or other relevant time units. It represents the leeway within a schedule. If a task has a slack time of a day, it means the task can be delayed by one day without impacting the overall project timeline. It provides flexibility for handling unexpected delays or adjustments in the project schedule.

Share this post

Maximize potential: Tackle’s automated time tracking & insights

Maximize potential: Tackle’s automated time tracking & insights