We’ve all been there. You make a simple change to your project plan, maybe increase scope, or add a resource, and all of a sudden everything changes on your plan (or at least it seems that way). Your resource load changes to 134.5%, or your Duration est.

However, it is better to step back and really understand how Microsoft Project schedules your tasks so that you can help Project do what you want it to do (versus cursing it or yelling at your screen – believe me, your office neighbors will certainly be happier).

The most important thing to know here is a very important formula. And that formula is very simple:

WORK = DURATION x UNITS
Or
W = D x U

Work = Level of effort of the task
Duration = How long is that task going to take
Units = How many resources am I applying to this task and how much of their time will be spent on that task.

Now, before we talk about Microsoft Project, let’s make sure we understand the application of this formula in real life terms.

Let’s take our first example which is a task to ‘Program a Module’. Let’s say this task is estimated to be 40 hours of effort and we are going to staff one resource who is going to work full time (8 hours per day for this example).

Per the formula, what would be the Duration of that task? Work = Duration x Units. 40 hours = Duration x 1 FTE. 5 days. Pretty simple so far, right? And it makes intuitive sense.

Now – let’s say that at some point during the project, we decide to add a 2nd FTE to that task. What do we believe should happen to that task? Our formula has now changed. Any ideas?

Well, typically for a programming type of task, when we add a 2nd resource, we want the Duration to decrease. In this example, the estimated Duration would decrease to 2.5 days. So our new formula looks like:

40 hours = 2.5 days x 2 FTE’s

Did you notice something about the new formula in comparison to the original one? Every piece of the formula changed – i.e. Units, Duration – except for one – Work. Work did not change. Work remained fixed. This becomes important when we get to Part 2 of this topic.

Let’s do one more example before we break for the day. Let’s say that we have a task to ‘Conduct a Training Course’. And let’s say we start with the same base formula – in this case that means that it is a 5 day class attended by 1 FTE and it will take 40 hours of effort. So again: 40 hours = 5 days x 1 FTE.

Let’s say that we make the same change we made in our first example. At some point during the project, a 2nd resource registers for the class. What will now happen to this task?

Well, you may have figured out that this is a different type of task than the first one. Just because someone new signs up for the class, it doesn’t mean that the task will take less time. There is still 5 days of content to cover in the class. So the Duration stays the same.

However, something in that formula needs to change, right? If we increased the Units, and Duration stays fixed, then what is the only other thing to change? Work! That’s right, the Work has to increase as a result. Again, we have to stay true to the formula (and if you think about it, it makes sense – now with 2 people in the class, 80 total hours of effort will be expended).

So our new formula is: 80 hours = 5 days x 2 FTE’s.

Remember that in this formula, Duration stayed fixed. Again, this becomes important when we go to Part 2. Join us in the next couple of days to talk about how to take what you’ve just learned and apply that to scheduling in MS Project!