The third, “Birthdays,” are birthdays automatically added to your Calendar from your Contacts app. The second, “All Day Events,” are events, again including multi-day events, that do not have a specific start and end time and are marked with the “All Day Event” checkbox.

The first, “Events,” are standard events, including multi-day events, that have a specific start and end time. The drop-down menus highlighted by the red box above represent the default alert time for each of three types of events. Select the Alerts tab from the top to see the default alert options: This will open the Calendar Preferences window. Once the Calendar app is up and running, head to Calendar > Preferences from the menus at the top. To adjust the default Calendar alert settings, first launch the Calendar app, which is located by default in your dock. If it’s not there, you can also find it in your Applications folder. Thankfully, you can change these default Calendar alert settings. The issue is that these default alert settings may not be ideal for every user. You can manually adjust the number and timing of the alerts for events as you create them, but the Calendar app also includes a default alert setting that can be automatically added to all of your events, even those of different types, such as birthdays. Most Mac users know that they can use the built-in Calendar app to keep track of their appointments and events, and a great feature of the Calendar app is that it can automatically alert you prior to a scheduled event. How to Change the Default Calendar Alerts on Your Mac

Turn off calendar notifications