ICS end dates are exclusive

Today I learned that per the spec, the DTEND value in an ICS file is exclusive for all-day events.

It makes sense but it’s not how most people think of date ranges.

I ran into this while making a small node script that takes a json array of events and generates an ICS file. This has been the most convenient way I’ve found to quickly bulk create events in Google Calendar. The only issue is the multi-day events were coming up a day short.

So for example if Spring Break is from March 16th - March 20th, then the end date would need to be March 21st:

DTSTART;VALUE=DATE:20260316
DTEND;VALUE=DATE:20260321

Pro tip: if you’re importing a lot of events into Google Calendar, create a brand new “test” calendar and import the .ics file into that calendar first to test it out that way if something is messed up you can just delete the calendar and try again. Otherwise you have to go through and manually find all the events that got added.