The governance calendar shows all relevant dates for the seasons and sprints. You can view them in a calendar view.

To add directly to your calendar, subscribe to the governance calendar.

https://calendar.google.com/calendar/embed?src=c_547fe085bcb8ca03492e7427fe6c5a58d95c08aeb627c0ceb35c19a0c1450c83@group.calendar.google.com&ctz=Europe/Lisbon