A successful subscription to an online calendar will allow you to receive additions, deletions and other changes automatically based on your programs refresh schedule. Some programs will populate changes immediately while some may take a couple hours. Most calendar programs will keep calendar subscriptions separate from your primary calendar. Additionally, having a calendar subscription will make it easy to copy dates from subscribed calendars to your primary one as a way to choose what events interest you.

Programs that support the use of iCalendar files include Microsoft Outlook, Apple Calendar, Google Calendar and various programs on smartphones. How you subscribe to an online calendar varies by client, but the internet is full of resources on how to subscribe to online calendars based on your device and/or client.

Files with an ICS extension are iCalendar files. They are plain text files with calendar data in them. Sometimes meeting requests are sent as an iCalendar file but these files also give the ability to subscribe to entire calendars (For example: US Holidays). Most email clients and calendar programs provide a way to subscribe to online calendars by providing a link to an iCalendar file.