ADAM ENGST 19 March 2025

Every time I travel, I vow to figure out exactly how time zone support works in calendar apps, and every time, I get caught up in whatever I’m doing and forget. Now it’s time to buckle down and see if I can wrap my head around the topic.

I’ll admit to some trepidation about this topic, as I’m uncertain I can even test all the possible scenarios. I’m sure frequent travelers and distributed workgroups have encountered issues that my testing won’t uncover. So, please, if anything I say below doesn’t align with your experience, let me know, and we’ll see if we can figure out why.

Time Zone Issues

The most common issue I encounter when traveling arises when I schedule a 1 PM lunch while I’m at home in Ithaca (Eastern Time), only for the alert to go off at 10 AM when I’m in San Francisco (Pacific Time). I’ve missed meetings at Macworld Expo because the alerts went off three hours earlier than I needed them.

Another issue I’ve encountered, though less frequently, is that when people in different time zones are invited to an event or share a calendar, it’s important to enter events so that they appear at the correct time in each person’s time zone. This usually works well, but if I’m significantly more technical than the other person, I worry that something I’ve done might confuse them.

Adding to the confusion is the fact that Apple’s Calendar app on the Mac includes a checkbox labeled “Turn on time zone support” that lets you pick a time zone for display, while the Calendar app on the iPhone features a Time Zone Override option that allows you to specify a particular time zone. Additionally, calendar apps like BusyCal and Fantastical manage time zone support in slightly different ways. How do these options influence what I see, and do they impact what others will see?

To better understand all of this, I set one of my Macs to Pacific Time (San Francisco), another to Greenwich Mean Time (London), and kept my iPhone on Eastern Time (Ithaca, New York). I created events on each device with their local times included in the title, experimented with toggling time zone support on and off, and switched the Macs between time zones to simulate traveling. Here’s what I concluded.

Events and Reminders Have Time Zones

The key point to understand is that every event has a time zone. All events automatically default to the local time zone, regardless of whether time zone support is enabled. However, if time zone support is turned on, you can manually set an event’s time zone.

Every timed reminder you create in Reminders is assigned to the local time zone, which can lead to confusion while traveling if you depend heavily on reminder alerts. I can’t find options to adjust time zones for reminders in Calendar, Reminders, BusyCal, or Fantastical.

Events may have associated time zones, but how they are displayed depends on two factors:

• The device’s time zone: When you travel to a new time zone, your iPhone, iPad, and Mac typically switch to it automatically, and all event times reflect the change. You can manually reset a device’s time zone, but doing so may cause confusion unless you are troubleshooting or testing. On the iPhone and iPad, you can find this option under Settings > General > Date & Time > Set Automatically. On the Mac, in System Settings > General > Date & Time, you’ll find separate switches for “Set date and time automatically” and “Set time zone automatically using your current location.”
• Calendar app time zone overrides: You can force the Calendar app on your iPhone, iPad, or Mac to act as though it’s in a specific time zone, making all event times reflect the manually selected time zone. On the iPhone or iPad, enable Settings > Apps > Calendar > Time Zone Override. I recommend avoiding this option because it’s buried and thus easy to forget about. On the Mac, go to Calendar > Settings > Advanced, select “Turn on time zone support,” and choose a time zone from the pop-up menu that appears in the upper right corner of the window.
  

When an event’s time zone differs from the device’s native or manually specified time zone, something will always indicate the difference. For instance, this event was created for 2 PM Eastern Time but is being viewed in Pacific Time; therefore, Calendar displays it at the adjusted time of 11 AM but notes the creation time in parentheses.

Reminders are less obvious. I created a reminder for 4 PM on a device set to Pacific Time. When I view that reminder on a device set to Eastern Time, it shows up at 7 PM in Calendar (left) and Reminders (right), but neither app indicates its original time zone. (The title does, but I did that solely for clarity during testing.)

What About the Floating Time Zone?

While traveling to San Francisco for Macworld Expo, I often encountered the need to juggle multiple meetings each day. I didn’t want to schedule them based on my Eastern time zone because then they’d be at the wrong time once I arrived in San Francisco. At the same time, enabling time zone support and setting them to Pacific Time was tricky since they appeared three hours later on my calendar at home before I left. If I scheduled a lunch meeting for noon on Tuesday, and it showed up at 3 PM, it was all too easy to agree to another lunch that day since noon would seem available.

The answer is the “floating time zone,” which isn’t tied to any specific time zone. Instead, events using the floating time zone appear at the same time regardless of which time zone is currently being observed. The floating time zone first appeared in 1998 in RFC 2445, the specification for the proposed iCalendar standard. Apple seems to be the only major player that has adopted it in a significant way.

The floating time zone is helpful for individuals who are managing their own calendars across multiple time zones and sync between devices using iCloud. If you schedule lunch for noon on Tuesday, it will appear at noon on Tuesday, regardless of where in the world you are.

Unfortunately, the floating time zone isn’t a panacea:

• In Calendar, you can create floating time zone events only on the Mac. For inexplicable reasons, the Calendar app on the iPhone and iPad displays floating time zone events correctly but doesn’t let you create them. The same is true of Calendar in iCloud.com. Both BusyCal and Fantastical allow you to create these events on the Mac and iPhone/iPad.
• Neither Google Calendar nor Microsoft Exchange supports floating time zones, but if you use them only to sync among Apple devices, you might be able to get away with it. As I understand it, editing an event with Google Calendar will switch to a fixed time zone, while Microsoft Exchange will remove the time zone information (which may have roughly the same effect as the floating time zone—I can’t easily test that). Other calendar apps might not support floating time zones correctly, either.
• The floating time zone is appropriate only when you’re traveling between time zones. If you use it to arrange a 4 PM video call with a colleague in a different time zone and you both attempt to join at 4 PM local time, you’ll end up connecting at different times.
• The semi-annual absurdity of Daylight Saving Time adds yet another complication: floating time zone events don’t take into account the fact that local time has sprung forward or fallen back. It’s real governmental inefficiency!

A Few Common Scenarios

I’m sure this isn’t an exhaustive list, but some common scenarios that require thinking about time zones include:

• Traveling to another time zone: When scheduling events for a future trip, you have two options. You can either manually set the event time zone to match the destination or use the floating time zone. Both methods will ensure the events appear at the correct time once you arrive. I prefer the floating time zone because it makes visualizing my schedule on the other end easier before I leave.
• Creating events while away: The same issue arises in reverse if you need to schedule a doctor’s appointment at home, for example, while you’re away in a different time zone. You can manually set the time zone to your home zone or use the floating time zone.
• Dealing with trips through multiple time zones: For complex itineraries, you may want to create events that start and end in different time zones. That’s not possible in the macOS version of Calendar, but it is on the iPhone and iPad, where a Time Zone option appears under both the Start and End time pickers. The Mac version can display such events once created. (Thanks, Jolin!)
  
• Editing timed reminders manually: Unfortunately, there is no solution for timed reminders. They are always set to their local time zone, which means they will be incorrect in every other time zone. If you depend on regular timed reminders for medications or the like, you’ll need to edit them manually when you arrive at your destination and again when you return home. Apple’s Medicationsreminders notice time zone changes and ask you what to do with your particular medications (see “An Apple a Day: iOS 16 Medications Feature Provides Alerts, Logging, and Peace of Mind,” 7 October 2022). Consider using the independent reminder app Duefor consistent “wall time” reminders (see “Just Due It: Persistent Notifications for Tasks,” 6 July 2024).
• Scheduling calls with distant colleagues: When creating an event and inviting someone in another time zone, you don’t need to do anything special. The event should automatically be set for your local time zone, and when they accept the invitation, it will appear at the correctly adjusted time for their location.
• Shared workgroup calendars: I assume everyone in this situation already knows how to manage time zone-aware scheduling, but once again, creating all events in local time will have the desired effect for everyone viewing a shared event from a different location. However, organizing such events may require more thought, as everyone must determine if they’re available at whatever 10 AM Eastern corresponds to in their local time zone. Numerous websites will help you visualize possible time overlaps; World Time Buddy seemed particularly well-designed.
• Picking a good time for a global webinar: We ran into this back in the Take Control days when we wanted to host live events. Once we settled on a time, we would share an ICS file containing the event details for those who could import it into their calendars. It used our local time zone and adjusted itself for everyone else after import. For those who kept paper calendars or just wanted to know if that time would work for them, the Every Time Zone site does a good job of illustrating how times—and dates—shift around the world.

If you know of any other scheduling situations involving tricksy time zones, please share them in the comments, and I’ll consider adding them.