What is the best source for finding the most accurate and up to date P/E ratio for a stock?

I feel like many times a stock’s price will have a significant drop (such as what happened on Friday) and my first reaction will be to go and check what its new P/E ratio is to decide how attractively it might be priced or not.

Depending on the source I check, sometimes I’ll see different P/E ratios and I find that incredibly frustrating because I assume that it’s because some sources aren’t updating their info in a timely enough manner

Short of finding a company’s earnings reports and calculating the P/E ratio myself, what’s the best source to use for finding the most accurate and up to date P/E ratio for a stock?