What Is iCal?

iCal is the everyday name for iCalendar, an open file format for sharing calendar data such as events and to-dos between apps and websites. In hotel and rental distribution, an iCal link lets one booking site read another site's booked and blocked dates, so a night sold on one is closed on the other.

Last updated: October 2026

How iCal works

iCalendar is an internet standard. RFC 5545, published by the IETF in September 2009, defines it as a data format "for representing and exchanging calendaring and scheduling information", independent of any particular calendar service or protocol (RFC 5545). It replaced the original RFC 2445 and defines building blocks called components, including VEVENT for an event, VTODO for a to-do and VJOURNAL for a journal entry (RFC 5545).

The data travels as plain text. Its registered media type is text/calendar, and files use the .ics extension, or .ifb for free/busy time (IANA).

The format dates from 1998, when the IETF Calendaring and Scheduling Working Group created it, with Frank Dawson of Lotus and Derik Stenerson of Microsoft as the spec authors. It is heavily based on the earlier vCalendar format (.vcs) (Wikipedia). The format is sometimes called iCal, which was also the name of Apple's calendar app until 2012. Apple's app is one implementation of the standard among many (Wikipedia).

Booking sites use the format as a feed. One site publishes a calendar URL, and another site subscribes to that URL and checks it on a schedule. On Airbnb, a host exports the Airbnb calendar URL to paste into sites such as Vrbo or Booking.com, and imports those sites' URLs into Airbnb; imported URLs must end in .ics (Airbnb Help).

Each site sets its own schedule. Airbnb updates its calendar automatically every 3 hours, offers a manual refresh and rate-limits update requests (Airbnb Help). On Vrbo, imported events can take up to 20 minutes to appear on the web dashboard, and the owner app syncs every 30 minutes (Vrbo Help).

The feed carries a narrow set of data. Airbnb's help article covers booked and blocked nights (Airbnb Help). Booking.com's calendar sync imports and exports booked or closed dates (Booking.com Partner Hub).

Why it matters for hotel distribution

Airbnb, Vrbo and Booking.com all accept iCal links (Vrbo Help).

The first limit is timing. Every feed is checked on its own schedule, so some time always passes between a sale on one site and the block on the next. Booking.com states that "calendars aren't synced in real time and can take up to two hours to refresh" (Booking.com Partner Hub). The manual for Smily (BookingSync) says its iCal connection is one-way, is "not instant" and can take up to 6 hours to update. Tentative bookings are not shown as blocked, and the manual advises against instant booking on iCal-connected channels because double bookings become more likely (Smily manual).

Each site also caps what it accepts. Vrbo shows imported events for up to the next 365 days and allows up to five imported calendars per property (Vrbo Help). Airbnb's imported calendars cover up to 2 years of data, and an imported calendar cannot be paused, only disconnected and reconnected (Airbnb Help).

The biggest limit for hotels is eligibility. Booking.com offers calendar sync only to properties with 20 room types or fewer, a maximum of one unit per room type, and no connectivity provider (Booking.com Partner Hub). Vrbo does not let properties managed through third-party property management software import calendars (Vrbo Help). A hotel with several identical rooms of the same type falls outside Booking.com's rule. Booking.com suggests such properties consider a connectivity provider, which "can give you access to advanced features" (Booking.com Partner Hub).

iCal compared with other connection types and formats

 What it isHow it relates to an iCal feed
iCal (iCalendar) feedA calendar file at a URL that another site checks on a scheduleShares booked and blocked dates one way, with a delay set by each site
Channel managerSoftware that connects a property's reservation system to each channel and keeps rates, availability and booking rules up to date What is a channel managerBooking.com suggests it to properties that cannot use calendar sync Booking.com Partner Hub
CalDAVA protocol for reading and editing calendars stored on a server (RFC 4791) RFC 4791Used by calendar apps; a booking site's iCal feed is a plain file read on a schedule

Frequently asked questions

What is an iCal link?
An iCal link is a web address that points to a calendar in iCalendar format, usually ending in .ics. You copy the export link from one booking site and paste it into the import field of another, which then reads your booked and blocked dates on its own schedule. Airbnb requires imported links to end in .ics.
What is the iCal format?
The iCal format is iCalendar, the internet standard set out in RFC 5545 for representing and exchanging calendar and scheduling information. The data is plain text with the media type text/calendar, and files use the .ics extension, so an iCal file and an ICS file are the same thing. The format grew out of the older vCalendar format (.vcs).
What is an iCal feed?
An iCal feed is a calendar file that one site publishes at a fixed URL and other sites subscribe to. Each subscriber checks the URL on its own schedule and copies the booked and blocked dates it finds. Airbnb updates its calendar every 3 hours, and Vrbo accepts up to five imported calendars per property, showing events for the next 365 days.
Is iCal the same as a channel manager?
No. iCal is a file format that shares booked and blocked dates between sites, one feed at a time, on each site's schedule. A channel manager is software that connects a property's reservation system to the channels where it sells rooms and keeps rates, availability and booking rules up to date on all of them.
How often does iCal sync update (and why is my iCal not syncing)?
Each site sets its own timing. Airbnb updates every 3 hours and rate-limits requests, Booking.com can take up to two hours to refresh, Vrbo's owner app syncs every 30 minutes, and Smily reports delays of up to 6 hours. If dates are missing, check that the link ends in .ics and that the channel allows iCal for your property; Booking.com excludes properties that use a connectivity provider, and Vrbo excludes properties managed through third-party property management software.
Is iCal sync good enough, or do I need an API connection?
iCal is not real time, so a booking can land on a second site before the next check. Smily advises against instant booking on iCal-connected channels because the risk of double bookings is high. Hotels with several units per room type cannot use Booking.com's calendar sync at all; Booking.com suggests a connectivity provider instead.

Related terms

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Where Jetstream fits

iCal shares booked and closed dates between a few sites (Booking.com Partner Hub). Jetstream builds an AI channel manager that connects a property's reservation system to the channels where its rooms are sold and keeps rooms, rates and availability accurate on each one, managed from one place.

See Jetstream's AI channel manager Book a demo