Is High Float Justified?

“Never do today what you can put off till tomorrow. Delay may give clearer light as to what is best to be done.”

- Aaron Burr

In this check, DCMA is examining tasks with a large amount of float and asking whether the rationale for the high float is acceptable. Let’s start with what we mean by float.

What is float?

A simple explanation of float is the amount of time a task can slip before it impacts the finish date of the project. If a task has positive (greater than zero) float, that means that it is not critical, meaning it can slip a certain amount before it pushes the project’s finish date out. If a task has four days of float, for example, it can be delayed by up to four days without impacting the project’s finish date.

Using the train example, float is how far you can push the train on one end before the other end moves:

How is float calculated?

Float is a byproduct of the critical path calculation. During the computation of the critical path, a task’s earliest and latest start dates are computed. If there is four day’s difference between the early and late start dates, the task is said to have four days of total float. When a task’s float is calculated to be zero (or a negative number), it is considered to be critical.

What does DCMA consider to be “high” float?

DCMA looks at tasks with float higher than 44 days. How did they come up with this number? There are roughly 22 weekdays in a month, so there are approximately 44 weekdays in two months. If a task has 44 days or more of float, DCMA will expect and examine the rationale for the high float value.

Why does DCMA look at high float?

If a task is finishing 44 (or more) days before it needs to, it’s reasonable to ask why it’s starting as early as it is. Could the assigned resources be doing more critical work? Are there successors to the task that are missing?

Tasks with high float aren’t necessarily bad per se, but they do invite scrutiny to ensure there is justification for the high float.

How do I see float in Microsoft Project?

It’s there, really it is. Microsoft, with their infinite desire to make scheduling simpler, decided to call float something else: slack. As in “how much slack is there in this rope?” There are two problems with this renaming. First, the rest of the world calls it “float.” Second, when I visualize slack, I think about how far I can pull a rope before it starts pulling whatever’s at the end of it. But in the metaphor, we’re considering how far the task’s finish date can be pushed before it starts moving the project’s finish date.

Next steps

If DCMA’s threshold (5%) is exceeded for any tasks whose float is greater than 44 days, examine (and be prepared to justify) why these tasks are starting so much earlier than they need to start.

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