How to Sync Fastmail Calendar with Google Calendar

The short version

Your calendar lives in Fastmail, but something you rely on only reads Google: a booking tool, a client's scheduling setup, or an Android phone. There are two good ways to sync a Fastmail calendar with Google Calendar, and both let you keep working in Fastmail.

The free way: publish a link from Fastmail and add it in Google Calendar. It costs nothing extra, but the link is read-only, anyone who has it can view your events, and Google doesn't say how often it checks for updates.

The CalDAV Bridge way: it copies your Fastmail events into a Google calendar on a schedule and keeps the copies up to date. Edits you make in Fastmail show up in Google. If an invite went to the address you connect with, the Google copy has a link to answer it.

One thing to clear up first, because it's easy to land on the wrong tutorial: Fastmail has its own built-in Google connection, but it runs the other way. Fastmail describes it as syncing a calendar from another service while being able to view and manage it from your Fastmail account. That's Google into Fastmail. This guide is the reverse: your Fastmail events, showing up in Google.

Sold already? Skip ahead.

Have a Fastmail app password and your Fastmail CalDAV address ready.

Get started with Google

Show Fastmail in Google with a published link (free)

Fastmail can publish any calendar as a link, and Google Calendar can subscribe to it. No new account and no app password.

In Fastmail:

Open Settings, then Calendars.
Find the calendar you want to share and click to edit it.
In the Publish section, turn on "Full event details" to share everything, or "Free/busy information" to share busy times only.
Copy the URL, then click Save to activate it.

Then in Google Calendar, on a computer:

Find Other calendars and click Add other calendars.
Choose From URL.
Paste the link and click Add calendar.

Your Fastmail events appear under Other calendars in Google. A few honest catches:

Anyone with the link can view it. In Fastmail's words, "The URL is read-only, and can be viewed by anyone who has the link." Fastmail also says "URLs are not guessable," but treat the link like a password. You can reset it or turn publishing off from the same screen.
It's for looking, not editing. The link is read-only, so keep editing in Fastmail.
Google decides when to check for new events, and Google's help page for adding a calendar by URL doesn't say how often that happens. So there's no stated time for a new event to show up.

If that's all you need, you're done. If you want events copied on a schedule, want to answer invitations from the Google copy, or don't love the anyone-with-the-link part, keep reading.

Connect Fastmail with CalDAV Bridge: what you need

CalDAV Bridge is a small tool that does one job: it copies events from your calendar into a Google calendar and keeps the copies in step. Three things to have ready:

A Google account to sign in with.
A Fastmail app password. Your regular password won't work here; Fastmail's server settings page says "You cannot use your regular Fastmail password." The next section shows how to make one.
Your Fastmail CalDAV address, covered in the section after that.

One plan note before you start: Fastmail's Basic plan doesn't include CalDAV. From Fastmail's app passwords page: "Users on a Basic plan will not be able to use Fastmail on third-party mail clients or create app passwords, as Basic plans do not include access to IMAP, SMTP, CalDAV, or CardDAV." If you're on Basic, you can't connect Fastmail to CalDAV Bridge.

Create a Fastmail app password

An app password is a separate password that Fastmail makes for one app. Here's the path, from Fastmail's app passwords page:

In Fastmail, open Settings, then Privacy & Security.
Open Connected apps & API tokens, then Manage app passwords and access.
Click New app password.
If a "Verify it's you" box appears, enter your Fastmail password and click Continue.
Pick a name for the password, or choose Custom... and write your own. Something like "CalDAV Bridge" makes it easy to recognize later.
For data access, the default "Mail, Contacts & Calendars" includes calendars. Fastmail says you can also limit an app password to calendar data only, if you'd rather.
Click Generate password. The next page shows the password, so copy it now.

Fastmail suggests testing the app before you click Done, which is good advice: paste the password into CalDAV Bridge first, then come back and click Done. You can disable or remove an app password from the same screen at any time.

Find the Fastmail CalDAV address

Fastmail's CalDAV address is:

https://caldav.fastmail.com/

That's from Fastmail's server names and ports page, which lists it for third-party calendar apps. One more detail on that page matters. For the username, it says "Your Fastmail email address, including the domain." and is specific about which one: "You must use the username you used to sign up your account; other addresses will not work." Use your sign-up address, not an alias.

If the address above doesn't connect, Fastmail has a fallback: in Settings, then Calendars, click Export on a calendar. The popup shows that calendar's own CalDAV URL, which you can paste instead.

Open CalDAV Bridge and sign in with your Google account.
In the dashboard, choose Connect a CalDAV account.
Paste https://caldav.fastmail.com/ into the field labeled CalDAV server. With or without the https:// part is fine, because CalDAV Bridge fills in what's missing. As you type it, the form reminds you that Fastmail needs an app password and links to Fastmail's help page, in case you skipped ahead.
In Username, enter your Fastmail sign-up address. In Password, paste the app password you just made.
Click Connect. Nothing is saved until the connection check passes. If the short address doesn't connect, use the per-calendar URL from the Export popup instead.
If your Fastmail account has one calendar, it connects on its own. If it has several, a Select a calendar step lists them with the first one picked, so choose the one you want. Each connection covers one calendar.

There's no one-click button for Fastmail the way there is for iCloud and Zoho, which is why you paste the address yourself.

After you connect, the dashboard shows a short blue note saying caldav.fastmail.com isn't in the quick-setup list yet and has been noted as a possible addition. That's not an error. It's just a note.

Find your events in Google Calendar

CalDAV Bridge adds one new calendar to your Google account, named Synced Calendar (CalDAV Bridge). Every calendar you connect feeds into it, and it can't read, change or delete your other Google calendars.

A few things to expect:

Events from 30 days back to 365 days ahead get copied.
A big calendar can take more than one sync run to copy over, so a long history may appear in waves. There's a Sync now button on your dashboard if you don't want to wait, though one run won't finish a huge import.
If you use a booking tool, check which Google calendars it looks at and make sure it includes Synced Calendar (CalDAV Bridge).

Limitations to know

Worth reading before you rely on this day to day. Here's what you'll actually see:

Editing in Google does nothing to Fastmail. It's a one-way copy: events go from Fastmail into Google, and edits you make to the copies in Google don't go back. Keep editing in Fastmail.
Invitations get a reply link. If an invite was sent to the same address you use as the Username when you connect Fastmail, the Google copy ends with a plain-text link in the event description. Open it and you get Accept, Maybe and Decline, and CalDAV Bridge sends your answer back to your Fastmail calendar. Answering the event in Google Calendar itself doesn't send a reply. If the invite went to a different address, like an alias, the event still copies but there's no link.
Nobody gets notified. CalDAV Bridge doesn't send invitation emails or updates to anyone when it copies events, so copying a calendar full of invites won't email the people on them.
One changed occurrence of a repeating event may not carry over. If you move, edit or delete one occurrence, Google may keep showing the old time. That happens when the calendar saves the change as a one-off, and one-off changes aren't synced yet. A booking tool reading the copy would then block the old time and leave the new time open. If the change is saved on the repeating series instead, the Google copy updates on the next sync.
Free stays Free, everything else is Busy. Events marked Free in your original calendar stay Free in Google. Everything else shows as Busy.
Timing is a target. The Free plan checks roughly every hour and Pro roughly every five minutes. A change you make in Fastmail doesn't show up the moment you save it.
Old deleted events can linger. If you delete an event that's more than 30 days old, it can stay on the Google copy, since only events from 30 days back to 365 days ahead are synced.
Other apps that edit the copies get overwritten. If something else edits the copied events in Google, those edits are replaced the next time the event changes in Fastmail, and deleted copies come back on the next sync. Treat the Google calendar as read-only.

If the connection stops working

A few things to check, in order:

The error message may not say what's wrong. A failed connection shows "Couldn't connect:" followed by a technical message from the connection check. It won't always tell you whether the password or the address is the problem, so work through the checks below.
App password, not your regular password. Fastmail says you can't use your regular password. If you typed your sign-in password, make an app password and use that instead.
Username is your sign-up address. Not an alias: the address you signed up with, including the domain.
Basic plan has no CalDAV. If you're on Fastmail's Basic plan, third-party CalDAV access isn't included.
Form messages. "All fields are required." means something was left blank. "That server didn't report any calendars to sync." means the check ran but no calendars came back, so make sure the account has a calendar.
The blue note about the quick-setup list isn't an error.
Free plan limit. The Free plan covers one connected calendar. If you already have one and try to add another, you'll land on the upgrade page.
Removed the app password in Fastmail? Fastmail says removing one stops the app from accessing your account, so make a new one and reconnect. You can also disconnect a calendar from your CalDAV Bridge dashboard at any time, and choose whether to keep or delete the events it copied to Google.

Pricing and the founder offer

The Free plan is $0 and covers one connected calendar, checked roughly every hour. Pro is $2.99 a month or $12 a year, with no set limit on calendars, checked roughly every five minutes. Those are targets, not promises, and every plan has a Sync now button. Details are on the pricing page.

Founder offer: enter the code FOUNDER at checkout and Pro is free for life. It's first come, first served with limited spots, a thank you to the early adopters helping shape this.

On privacy: your calendar password is encrypted before it's stored, and so is the Google sign-in token. CalDAV Bridge stores the connection details and the event information it needs to keep the copies in sync. The privacy policy has the full picture.