For example when I calculate the PEG of Microsoft (for the fiscal year 2017):
For P/E ratio:
P/E Ratio = Price per Share (last price before 10-k filing) / EPS (diluted)
= 68.93 / 2.71
= ~25.43
But, Morningstar states a P/E of 30.23.
For EPS growth rate and PEG:
Growth rate = 2.71 (2017 EPS) / 2.10 (2016 EPS) - 1
= ~0.29 = ~29%
PEG = 25.43 / 29
= 0.88
But, Morningstar states a PEG of 2.78
I'm interessted in how and why my calculation differs so much from Morningstar data, and is my calculated PEG even usable?