An .ics file is a calendar event written out as plain text, which is why it looks so unhelpful sitting in your inbox. To open an ICS file, double-click it: your computer's default calendar app reads the file and offers to add the event to your diary. On a Mac that's the whole answer. Windows usually manages it too, apart from one version of Outlook that gets its own section below.
Before any of that, one check. If the email came with Accept, Tentative and Decline buttons, it's a meeting invitation and there's nothing to open. Press a button and the event goes in on its own. The rest of this page is for the attachment that just sits there as invite.ics.
What double-clicking does
On a Mac, the file opens in Calendar, which asks which of your calendars the event should go in. Pick one and it's in.
On Windows, the file opens in whichever app is registered for .ics. On a Windows 11 machine that's now Outlook, since the old Mail and Calendar apps stopped working at the end of 2024. You should see the event on screen with a Save button, and nothing is added until you press it.
If the wrong app opens, or the file lands in Notepad as a wall of capital letters, the file association is pointing somewhere unhelpful. Open Settings, go to Apps, then Default apps, type .ics into the search box, and choose the app you want from the list. That holds for every .ics file from then on.
Opening an ICS file in Outlook
There are 3 Outlooks now and they behave differently, which is where most of the confusion on this subject comes from.
New Outlook
In the new Outlook for Windows, double-clicking an .ics file often appears to do nothing at all. No window, no error. The import dialog has in fact opened, but it's sitting in the Calendar view, so switch to Calendar and you'll usually find it waiting there, asking which calendar the event should go in. Choose one and click Import.
Microsoft's own suggestion, on the support thread about this, is to right-click the file, choose Open with, then Choose another app, pick Outlook and tick Always use this app. Quite a few people on the same thread report that this doesn't take either, and their fallback is dragging the file straight into the calendar window. The thread has been open for over a year, so I wouldn't wait for a fix.
Classic Outlook
Classic Outlook does the opposite: double-click and the event opens immediately as an appointment. Save it and it's in. The catch is that it always lands in your primary calendar and there's no way to choose another one from that window.
If you need it in a different calendar, a shared team one say, don't double-click. Open File Explorer, find the file, and drag it onto the calendar you want in the folder pane on the left of Outlook. It goes where you dropped it.
Outlook on the web
Go to the calendar, click Add calendar, then Upload from file. Browse to the file, choose the calendar it should land in, and click Import.
Adding an ICS file to Google Calendar
Google Calendar is the one that won't take a double-click, a drag, or anything else from the desktop. You import the file through its settings, and it has to be done on a computer.
On a computer
Open Google Calendar in a browser, click the settings cog, then Settings. In the left-hand menu click Import and export, then Select file from your computer. Pick the .ics file, choose which calendar the events should go in, and click Import.
Two things Google says in its own instructions that are easy to miss. The file has to be 1MB or smaller. And guests and conferencing details are dropped on import, so if the event arrived with a Meet link in it, that link won't be in your copy.
On a phone
The Google Calendar app has no import screen. Google is plain about it: importing is done on a computer. The route that works on a phone is opening the file from the email it arrived in, covered in the phone section below. Failing that, import it on a computer and the event syncs down to the phone on its own.
If Google says something odd
"Processed zero events" nearly always means you clicked Import twice and the events went in on the first click. Look at the calendar before you try a third time.
"Processed 12 of 40 events" means the file had entries Calendar couldn't read, which points at whatever produced the file rather than at you.
A message about Calendar being temporarily unavailable is usually the file being over the 1MB limit, which sounds like Google's problem and isn't. Split it into smaller files by date range and import them one at a time.
Apple Calendar on a Mac
Double-clicking covers it. If you'd rather choose the destination deliberately, it's File, then Import, then pick the file, or drag the file onto the Calendar window, which is quicker. Either way it asks which calendar to use.
One small thing from Apple's own notes: if the file carried a custom colour for the events, that's discarded on import. They'll take the colour of whichever calendar you put them in.
On an iPhone or Android phone
Neither Apple's Calendar app nor Google's has an import screen on a phone, so a file you've already saved to the phone often has nowhere to go. The way round it is to open the file from the email itself, before it's been saved anywhere.
On an iPhone, tap the attachment in Mail. You should get a preview of the event with an Add button, and a choice of which calendar it goes in. A file in the Files app should open the same preview when tapped.
On Android, tap the attachment in Gmail and Google Calendar should open with a preview of the event and a Save button. If the phone opens it in something else, or offers nothing, the reliable fallback is to import it on a computer, since the event then reaches the phone through the account.
So if a colleague is stuck, the thing to tell them is to go back to the original email and tap the attachment there, and if they've only got the file, to forward it to themselves and try again.
Reading one without adding it to your calendar
Sometimes you want to know what's in the file before committing it to your diary. Someone's sent you 40 events and you'd rather see what they are.
An .ics file is plain text, so right-click it, choose Open with, and pick Notepad on Windows or TextEdit on a Mac. You'll get something like this:
BEGIN:VCALENDAR
VERSION:2.0
BEGIN:VEVENT
UID:planning-day-nov-2026@yourcompany.com
DTSTART:20261112T100000Z
DTEND:20261112T160000Z
SUMMARY:Team planning day
LOCATION:Birmingham office
END:VEVENT
END:VCALENDAR
SUMMARY is the title, DTSTART and DTEND are the times, and the Z on the end of those means the times are in UTC, so they may not match your local clock. That's usually enough to tell you what the file is. For the rest of it line by line, how to create an ICS file walks through every field, and reading one is easier once you've typed one.
Opening the file this way changes nothing. It's a text file being read by a text editor, and your calendar never hears about it.
When it won't open at all
Four things account for most of it.
The file isn't really an .ics. Windows hides file extensions by default, so a file that was saved out of Notepad as invite.ics.txt shows in the folder as invite.ics and no calendar app will touch it. Turn on File name extensions in Explorer's View menu and you'll see what you've actually got.
Nothing is registered to open .ics files, which happens on a machine with no desktop calendar app. The default apps route above fixes it, or use the web version of your calendar and import instead.
The file itself is broken. A BEGIN line without its matching END, or a date with a digit missing, and most calendar apps refuse the file without saying why. If you can read it in a text editor you can usually spot it, and the where .ics files go wrong section on our generator page covers the less obvious faults.
And it's new Outlook, doing nothing on a double-click. See above. This one alone probably accounts for half the people who search for this.
If the events land but sit at the wrong time, the file worked and its timezone didn't. The times were written without one, or the file was made in a different timezone from the calendar that's reading it. The same page covers why that happens.
An imported event is a copy, and it stays a copy
This catches people well after the file has been opened and forgotten about.
Microsoft puts it about as bluntly as it can in its own documentation: when you import an .ics file, your calendar doesn't refresh the imported events, even if the calendar's owner makes an update. Google behaves the same way. The event in your diary is a snapshot of what the file said on the day you imported it.
So when the organiser moves the event a fortnight later, your copy sits there at the old time, and nothing in the file can tell you otherwise. Only a proper meeting invitation, sent through a mail system with the same event ID, can move an entry that's already in someone's calendar. Subscribing to a calendar by URL is the other way to stay current, and that's a different thing from importing a file.
Which is why an event that changes, and events do change, is better sent again as a fresh file with a plain sentence in the email saying what moved.
If you're the one sending these out from HubSpot, add-to-calendar links in HubSpot event emails covers the full set of links an event email needs. EventEngine builds the .ics from the HubSpot event record, so the file always says whatever the event currently says.
Questions that come up
How do I open an ICS file on Windows?
Double-click it and Outlook shows the event with a Save button. In new Outlook the dialog often opens silently in the Calendar view, so switch to Calendar if nothing seems to happen. If the wrong app opens, go to Settings, then Apps, then Default apps, search for .ics and choose Outlook.
How do I open an ICS file on an iPhone or Android phone?
Open it from the email it arrived in rather than saving it first. Tap the attachment and the phone's calendar app shows the event with an Add or Save button. Neither Google Calendar nor Apple Calendar has an import screen on mobile, so a saved file often has nowhere to go.
Can I open an ICS file without adding the event to my calendar?
Yes. Right-click the file, choose Open with, and pick Notepad or TextEdit. An .ics file is plain text, so you can read the title, dates and location without importing anything.
Is there a size limit on importing an ICS file?
Google Calendar accepts files up to 1MB. Larger files usually fail with a message saying Calendar is temporarily unavailable. Export the events in smaller date ranges and import them one file at a time.
Why did my imported events appear at the wrong time?
The times in the file were written without a timezone, or the calendar's timezone doesn't match the one the file was made in. Check the DTSTART line in a text editor: a trailing Z means the time is UTC.
