How to connect a CalDAV calendar
One open standard, one connect dialog, and a long list of calendars behind it: Zoho, Fastmail, Yahoo, Yandex, Apple iCloud, and any server you run yourself. 42min reads them for conflicts and writes every booking back.
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Which calendars speak CalDAV
CalDAV is the open standard for reading and writing a calendar over HTTPS. Five services get a preset in 42min with the server address already filled in. Everything else goes through the generic option, where you supply the address yourself.
Connect in 4 steps
The same four steps whichever service you are on. Only step 3 changes.
Generate an app password
Open your calendar provider's account security settings and create an app password for 42min. Most providers show it once, so copy it before you close the page. The connect dialog links straight to the right page for whichever service you pick.
Pick the service in 42min
Open Availability → Calendar, click Add Calendar, and choose your service from the provider list. The five presets already know their server address, so there is nothing for you to look up.
Fill in what your service asks for
Zoho adds a region selector. A generic CalDAV connection adds a Server URL field. Everything else takes your email address and the app password you just generated.
Say what each calendar is for
Tick the calendars that should block your booking page, then choose the single one new bookings are written to. An account can be connected and perfectly healthy while the calendar holding your meetings sits unticked.
Field-by-field reference, including every error the dialog can return, lives in the CalDAV and Apple iCloud help guide.
Connecting a server you host yourself
The generic CalDAV connection takes any server that implements the standard, which covers Nextcloud, Radicale, Baïkal, and the calendar app on a Synology NAS. Alongside your username and password it asks for a Server URL, and that means the DAV endpoint rather than the web interface you log into. Nextcloud publishes its at /remote.php/dav/; most other servers use /dav/. Your server's documentation will name it if neither fits.
Because 42min reaches your server from its own infrastructure rather than from your laptop, the address has to satisfy three rules before a connection will go through.
HTTPS on port 443
Traffic goes over TLS to the standard HTTPS port. A server answering on some other port is turned away, so publish it on 443 or put a reverse proxy in front of it.
A public hostname
The address has to be a DNS name that resolves on the public internet. IP addresses are rejected outright, along with loopback, private ranges, and link-local addresses.
One pinned origin
The address you enter becomes the only origin your credentials ever travel to, rechecked on every request. A redirect pointing at a different host stops the request instead of following it.
All three rule out the same shape of setup: a calendar behind a VPN, one on a home LAN, one on a machine only your office network can reach. The usual fix is a reverse proxy with a real certificate and a public DNS name, which is the same thing any other calendar client would need from outside your network.
What travels over the connection
The connection runs both ways, and it behaves identically whichever server is on the other end.
Busy times
Every calendar you tick for conflict checks is subtracted from your booking page. An appointment already sitting on your Fastmail or Nextcloud calendar closes that slot without you opening 42min.
New bookings
Each confirmed booking becomes a real event on the calendar you set as the write target. Rescheduling moves that event and cancelling removes it, so the calendar you already live in stays correct.
Meeting poll holds
While a meeting poll is collecting votes, its candidate times are held on your write-target calendar, so nobody quietly books a slot the group is still choosing between.
Repeating events, across servers that disagree
CalDAV servers differ in how much work they will do on a client's behalf, and recurrence is where that shows. 42min first asks your server to expand your repeating events itself, which is both fast and exact. A server that declines gets a plain query instead, and 42min works the occurrences out locally. The answer is the same either way: a weekly stand-up blocks every week. 42min remembers which of the two your server supports, so later checks go straight to the one that works.
When an event uses something that resists full expansion, that stretch of time is treated as busy rather than assumed free. Fewer bookable slots is a recoverable outcome; a double booking is not.
Three things a CalDAV connection leaves to other tools
- Invitations from your calendar server. The booking lands on your calendar without attendee lines, so your server never emails an invite of its own and nobody receives two. Your invitee still gets the 42min confirmation with an
.icsattachment for any calendar. - Additional attendees. An event type's additional attendees need a Google or Microsoft write calendar to be invited, so they are left off events written over CalDAV.
- Google Meet and Teams links. Both ride on their own vendor's calendar connection. Zoom works on any provider, and the phone, in person, and custom link meeting types work everywhere.
Everything else in 42min is indifferent to which calendar you connected. Round robin, group events, routing forms and meeting polls all behave the same, and a team can run one booking link with every host on a different calendar provider.
When the connection won't go through
“No CalDAV support was found at this address.” The Server URL points at something that isn't a DAV endpoint, usually the web interface instead of the calendar API. Look up your server's DAV path: Nextcloud uses /remote.php/dav/ and many others use /dav/.
“The calendar server could not be reached.” The hostname doesn't resolve from the public internet, or it answers somewhere other than port 443. A server on a home LAN or behind a VPN lands here too.
“The server rejected the username or password.” On any of the five presets, use the app password rather than the password you sign in with. If you rotated your account password recently, generate a fresh app password: most providers invalidate the old ones when the main password changes.
“Too many attempts.” Connection attempts are rate limited so that guessing credentials gets nobody anywhere. Wait a minute and try again.
Connected, but nothing is offered as a write target. 42min only offers calendars it has confirmed it can write to, which rules out subscribed feeds, holiday calendars, and calendars shared with you read-only. Create or pick a calendar you own on that account, then refresh it.
Connected to Zoho, but only one calendar appears. Zoho shares just your default calendar with calendar clients. Move the meetings you want protected onto it.
Connected, but the slots are wrong. Tick the calendar that actually holds your events for conflict checks. Adding the account selects nothing on its own.
CalDAV calendar FAQ
CalDAV is the open standard for reading and writing calendars over the web, published as RFC 4791 and spoken by most calendar services outside Google and Microsoft. It is what lets the calendar app on your phone talk to a server somebody else runs. 42min uses it the same way: it reads the calendars you point it at, and creates booking events on the one you choose.
Any calendar that speaks the standard
Zoho, Fastmail, Yahoo, Yandex, or the server in your own rack. Connect it once and let your booking page work from the calendar you already keep. Free, with no per-seat bill.
No credit card · Free plan · Every feature unlocked