© Sean Whitaker 2016
Sean WhitakerPass the PMP® Exam10.1007/978-1-4842-2074-0_15

15. Formulas to Remember

Sean Whitaker1 
(1)
ChristChurch, Canterbury, New Zealand
 
Communications
How many people in a communications network; n=number of people
$$ =nleft(n-1 ight)/2frac{nleft(n-1 ight)}{2} $$
PERT
Weighted average of three estimates (optimistic, realistic, and pessimistic)
$$ =left(O+left(4 imes R ight)+P ight)/6frac{left(O+(4R)+P ight)}{6} $$
Standard deviation (SD)
A PMBOK® Guide heuristic for calculating standard deviation from the mean
1SD either side of the mean ≈ 68%
2SD either side of the mean ≈ 95%
3SD either side of the mean ≈ 99.7%
$$ =left(P-O ight)/6frac{left(P-O ight)}{6} $$
Variance
The standard deviation squared
$$ ={left(left(P-O ight)/6 ight)}^2{left(frac{left(P-O ight)}{6} ight)}^2 $$
Planned value (PV)
How much you planned to spend on what you planned to have achieved. The total PV for the project is the budget at completion (BAC)
= planned % complete × BAC
Earned value (EV)
The value of the work performed expressed in dollars
= actual % complete × BAC
Actual cost (AC)
How much you actually spent on what you actually achieved
 
Budget at completion (BAC)
How much you originally planned for the project to cost and the total planned value (PV) for the project
 
Cost variance (CV)
The difference between what you have earned and what it cost at a certain point in time; positive is good; negative is bad
= EV – AC
Cost performance index (CPI)
Cost variance (CV) expressed as an index; above 1 is good, below 1 is bad
= EV/AC
Schedule variance (SV)
The difference between what you have earned and what you planned to have achieved at a certain point in time; positive is good; negative is bad
= EV – PV
Schedule performance index (SPI)
Schedule variance (SV) expressed as an index; above 1 is good, below 1 is bad
= EV/PV
Estimate at completion (EAC)
How much the project is forecast to cost at completion
= AC + ETC
= AC + (BAC – EV)
= BAC/CPI
= AC+[(BAC – EV)/(CPI × SPI)]
Estimate to complete (ETC)
How much more money it will cost to finish the project
= EAC – AC
Variance at completion (VAC)
Difference between what you thought the project would cost and what it actually ends up costing; positive is good; negative is bad
= BAC – EAC
To complete performance index (TCPI)
The rate at which you have to go to achieve the desired outcome of either BAC or EAC; above 1 is bad, below 1 is good
= (BAC – EV/(BAC – AC)
= (BAC – EV/(EAC – AC)
Point of total assumption (PTA)
The point in a form of fixed-price contract at which the seller assumes total responsibility for all cost increases
= target cost +((ceiling price – target price)/buyer’s % share of cost overrun)
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