There are several factors that will cause financial websites to report different P/E ratios. For starters, you must be cognizant of the specific earnings metric that is being utilized. Many sites will utilize diluted (GAAP) earnings when they do the calculation.
FAST Graphs defaults to “Adjusted (Operating) Earnings.” However, “Diluted Earnings (GAAP)” are available with FAST Graphs along with three (3) other metrics (“Normalized Basic Tax-Adjusted Earnings” “Normalized Basic Earnings” “Basic Earnings”). We also offer calculations based on Cash Flow or FFO and AFFO for REITs. The link below is describing the FAST Graphs blended P/E ratio. This approach is utilized with all the metrics that FAST Graphs offers.