# PMI Formulas

This is a very basic study aid for typing and memorizing the PMI’s Project Management formulas. The answers are available by scrolling down to a completed table below. You can use the first table to test yourself.

As recommended by Rita, I generally tried to express each formula description at least once in my own words. I find it helps me initially to understand them and later to recall them, but this does leave room for variance in interpretation. Feel free to advise me of any corrections, clarity needed, or suggestions.

 Acronym Name or Formula Interpretation EAD Activity Standard Deviation Activity Variance EV PV AC BAC CV SV CPI SPI EAC ETC VAC TCPI AWCS EAD AV SD Activity Range Project Expected Duration Project SD Project Range EMV Communication Channels PTA Final Fee Final Price Float Formula Formula Formula Formula   Notes:

1. Except for TCPI, the 4 letter formula acronyms are either dated or invalid.
2. EV comes first
3. Actual cost must be provided in the question
4. “Not enough information is provided.” is a possible correct answer
5. Variance formulas are EV – something
6. Index formulas are EV / something
7. Cost formulas use CV
8. Schedule formulas use PV
9. For variance, negative is bad. Positive is good.
10. For indices, > 1 is good. < 1 is bad.

### 14 comments to PMI Formulas

• Murali

Hi Mark,

Small Typo in the formulae listed..
Float Float = LF – LS or LS – ES Late Finish – Early Finish or Late Start – Early Start

I guess it should be Float Float = LF – EF or LS – ES Late Finish – Early Finish or Late Start – Early Start. (i.e, Late Finish – Early Finish).

Thanks for sharing all formulae at one place. I keep coming back to this page just to make sure I got my formula right (during my practice test).

Regards,
Murali

• mark

Hi Murali,

You are exactly right. Good catch. I’ve made the update (changing LS to EF) in the abbreviation column.

Best,
Mark

• Richard Wheeler

For the Project SD (Standard deviation of the project), shouldn’t the AVs be squared?
sqrt[AV^2 + AV^2 + AV^2 …]

Your definition of SD says, “The square root of the variance.” According to your formulas, it’s the other way around; SD is the square of the variance.

It’s important to sticklers for math to realize that the PMI formula for SD is a quick approximation. Using data for an exercise for the course I’m taking, the PMI formula consistently overestimated the SD by 30% to 40%, compared to the formula used in statistics.

I’ve been very frustrated with the number of inaccuracies and inconsistencies in the PMBOK. Could it be that they’re intentionally conditioning people to put up with less-than-Six Sigma quality?

• Dave

Nice Job! Thanks!

• mark

Thanks Dave!

It looks like formulas above are accurate. The Activity Variances are already squares (they are squares of the standard deviations) in your first example regarding Project Standard Deviation. So you do not square them again. You would be correct if it was written as: Project SD = sqrt[SD^2 + SD^2 + …] But this is the same as written above: Project SD = sqrt[AV + AV + …]

Similarly, Activity Variance is in fact the square of Standard Deviation and Standard Deviation is the square root of Activity Variance:

AV = SD^2
SD = ( P – O ) / 6
AV = [ ( P – O ) / 6 ] ^2
SD = sqrt[AV]

I don’t think the calculations should ever be off by the 30% – 40% you reference, if the underlying estimates are assumed to be accurate. If I provide 2 PMPs hundreds of work and cost estimates from my project team members, they should return me exactly the same standard deviation results. While my team members may have estimated inaccurately, it is precisely the value of standard deviation and activity variance to mitigate that error and increase the accuracy of planning.

Best,
Mark

• Richard Wheeler

Mark, I have a problem getting from the statistical definition of SD,

to

SD = ( P – O ) / 6

One simplification, EAD=M, got me close, but no cigar. My formula is higher than PMI’s by a factor of SQRT(3). I’ll post or send you my derivation if you like. Maybe you can spot my error(s).

• Linda

Thank you so much for this listing, I was going to take the PMP but I don’t have enough hours… so I will take the CAPM. I hope this will help me

• tariq badsha

In BAC formula where you are normalizing the remaining duration by CPI as well as SPI you are using CPI + SPI in the denominator. This should be CPI * SPI. Adding the two indices will give you a value of greater than one when in fact one or both are less than one

• […] A whole bunch of formulas: (Quiz Yourself!) http://markpreynolds.com/pmp/formulas […]

• Mark

Hi Tariq. You’re right and that is not a typo on my part. I’ve had that there since my studies, the reason being my prep guide: PMP Exam Prep 6th Edition, by Rita Mulcahy, lists the performance indexes as a sum on page 242, the only reference to it in the book that I’ve found.

I’ll update the post. Thanks!

• Michelle

I appreciate this it will help with my CAPM studies

• Michael

The formula for lease or buy was stumping me but what appears to work is to subtract the daily maintenance cost from the daily lease cost and divide the purchase price by the result gives you the amount of break even days.

• Pierre

Hey Mark, missing

NPV = (for i:1 to years do CF(i)/(1+d)^i done) – initial investment
Payback = numbers of years to have the payments of the initial investment (nominal : without anual discount rate or present , with NPV casf flows)
ROI = anual profit / investment
IRR, Internal Rate of Return = rate (d) to obtain NPV = 0 for a determined number of year. Find it by estimations.