SendGrid Stats are a bit deceptive

When reviewing open rates, click-through rates, and other metrics on SendGrid, you might assume the numbers are accurate—but they often aren’t. To get a true picture, grab a calculator and manually compute the raw data; you’ll notice discrepancies.

SendGrid calculates these metrics differently. Instead of basing the open rate on delivered emails, it calculates it against the entire list, which can lead to misleading results which are lower. So, my advice. Create an Excel sheet, put the raw data in and do your own calculations.