QR code type
Calendar event QR codes: how they work
A calendar QR code stores a minimal iCalendar VEVENT that phones offer to add to the calendar. Always store times in UTC with a trailing Z, or attendees in other timezones get the wrong hour. Nothing is added without the user confirming.
The payload
BEGIN:VEVENT
SUMMARY:Product launch
DTSTART:20260915T180000Z
DTEND:20260915T200000Z
LOCATION:Grand Hall, 12 King Street
DESCRIPTION:Doors at 17:30
END:VEVENT
Most phone cameras accept a bare VEVENT. Some stricter scanner apps want the full
BEGIN:VCALENDAR / VERSION:2.0 wrapper, which costs about 40 extra bytes. If the
code will be scanned by desktop tools, include the wrapper.
The timezone trap
Three ways to write a time, with very different outcomes:
| Form | Meaning | Use it? |
|---|---|---|
20260915T180000Z |
18:00 UTC | Yes, unambiguous everywhere |
20260915T180000 |
18:00 local to the reader | Only for genuinely local events |
TZID=Europe/London:20260915T180000 |
18:00 London | Correct but poorly supported in QR contexts |
Floating local time is the default trap: a conference at "18:00" scanned by an attendee
whose phone is still on another timezone lands at the wrong hour. Store UTC with the
Z suffix and let each device render its own local time.
All-day events
Use a date-only value with the VALUE=DATE parameter, and make DTEND the day
after the last day: the end is exclusive:
DTSTART;VALUE=DATE:20260915
DTEND;VALUE=DATE:20260916
Writing the same date for both produces a zero-length event that some calendars discard.
Recurring events
RRULE is part of iCalendar and technically encodable, but phone camera handlers
frequently drop it, creating a single occurrence. For a weekly class, point a
URL QR code at a hosted .ics file instead: the file can be updated
when the schedule changes, which a printed code never can.
Where these work well
- Conference and session signage, where attendees decide on the spot.
- Printed invitations and save-the-dates.
- Class and clinic schedules on a noticeboard.
- Exhibition labels for time-limited installations.
FAQ
Why does my event show at the wrong time for some people?
The time was stored as floating local time. Use UTC with a trailing Z (for example 20260915T180000Z), and every device converts to its own local time correctly.
Does the event get added automatically?
No. The phone shows a preview and the user confirms. Nothing is written to a calendar without their action.
Can I encode a recurring event?
The RRULE property exists, but phone camera handlers often drop it and create a single occurrence. Link to a hosted .ics file instead for anything recurring.
How do I make an all-day event?
Use DTSTART;VALUE=DATE with a date only, and set DTEND to the day after the last day: the end date is exclusive.