It has been more than two decades since I studied Calculus. Honestly, when Siraj Raval recommended it as part of his Learn Machine Learning curriculum (https://youtu.be/Cr6VqTRO1v0), I anticipated it being perhaps my greatest challenge. I really don’t know why, though, since I did well when I last took it.

That concern seems to have been unfounded. Siraj, and others, pointed to one YouTube channel: 3Blue1Brown. So, either Calculus is much easier than I remember, or 3Blue1Brown has a way of making it look that way.

Either way, whether you need to learn Calculus for the the first time or you just need a refresher, I recommend 3Blue1Brown’s Essence of Calculus playlist: https://www.youtube.com/playlist?list=PLZHQObOWTQDMsr9K-rj53DwVRMYO3t5Yr.