Later this week, Google will update its Play Services suite to allow Android users to add and manage reminders with Calendar.
Once the update is live, it will be possible to add reminders to Calendar throughout the operating system. Google Now, for instance, will allow users to add one using their voice. Likewise, Inbox and Gmail will allow users to do the same. Once a reminder is added to the app, it will appear alongside the events Calendar normally tracks.
Check out the YouTube video below, which details the functionality in brief.
Source: Gmail blog