The calendar you see below has all the ATP and WTA tournaments for 2018.
If you're using Google Calendar, you can add these calendars (ATP and WTA separately, for those who only want one of them) to your schedule with a couple of clicks (in fact, if you've already added a previous version to your Google Calendar, the 2018 events are already there!).
If you're using a different calendar, you can import the calendars separately in iCal format for the ATP, and the same for WTA (iCal). Or, you can just use the calendar in this post, if you wish!
Enjoy!
Anna