More Fun with Project Actual Costs

A couple of weeks ago, I spent some time figuring out how actual costs were calculated within Microsoft Project.  That ended up being a series of 3-4 blogs posts, which I felt captured the meat of the discussion.

Well, over the weekend, I started playing with Microsoft Project again, and I realized that there’s a key bit of functionality in there which definitely adds to the discussion.  I am not sure how it adds to the discussion, but it definitely provides another building block in our common understanding of some behind the scenes calculations.

In this case, I have a new blank project.  I add a single 10 day task to this project.

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I set the Fixed Cost for the activity to $10,000.

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Now this is where it gets interesting.  Watch what happens when I enter a “1” in the Actual Work column.

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First, we see that Work is now populated with 80 hours – which makes sense.  That’s 10 days X 80 hours = 80.  Ok.

Next, we see that Actual Cost has now been calculated as $100 or 1% of the total Fixed Cost.  For the record, our Actual Work comprises .0125 of the Work.

Now, I change the Actual Work to 2 hours.  I would expect Actual Cost to change to $200.

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Nope – I end up with $300.

What’s going on here?  As far as I can tell, here’s the calculation being performed behind the scenes:

(Round(100*[Actual Work]/[Work])/100)*[Fixed Cost]

…which, if broken down, yields the following steps:

  1. Divide Actual Work by Work.  In this case, with a 1 in the Actual Work, that yields .0125.
  2. Round that to the nearest hundredths.  That changes .0125 to .01.
  3. Multiply that number by the Fixed Cost field: .01 * $10,000 = $100.

Let’s try that with 2 in the Actual Work column:

  1. 2/80 = .025
  2. Round .025 to .03
  3. .03 X $10,000 = $300.

…and our calculation seems to work consistently.

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More Fun with Project Actual Costs

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