How to Sync Your Calendar With a Scheduling App

To sync your calendar with a scheduling app, open the scheduler's calendar or integrations settings, connect your calendar account (Google, Outlook, or Apple), and choose which calendars it checks for conflicts and where new bookings land. Most tools — Calendly, Cal.com, Acuity, SavvyCal — do this in three or four clicks for Google and Outlook.

The part nobody tells you up front: the experience is very different depending on which calendar you use. Google and Outlook get clean, real-time, two-way sync. Apple Calendar does not — and as of 2024, the most popular scheduler dropped iCloud support entirely. If you live on a Mac or iPhone, that detail changes everything.

I build hora Calendar, a native calendar for Mac, so I spend a lot of time in the weeds of how calendar data actually moves between apps. Here's the practical version.

What "syncing your calendar with a scheduling app" actually means

A scheduling app (also called a booking tool) shows other people your open time slots and lets them book you. For that to work without double-booking yourself, the scheduler needs to read your real calendar — your meetings, your focus blocks, your dentist appointment — and treat that time as unavailable.

So "syncing" is really two separate jobs:

Read availability: the scheduler looks at your calendar and hides any slot you're already busy.
Write bookings: when someone books you, the scheduler creates an event on your calendar.

Whether a tool does one, the other, or both is the difference between one-way and two-way sync — and it's the first thing to check.

One-way vs. two-way sync (and why it matters)

This is the single most important concept, so it goes first.

One-way sync moves data in a single direction. Usually: bookings flow out of the scheduler and onto your calendar. But events already on your calendar don't flow back to block your availability. Result: people can still book you during your existing meetings.
Two-way sync goes both directions. New bookings appear on your calendar, and events on your calendar block your booking page automatically. This is what prevents double-bookings.

When a tool advertises "calendar sync," confirm it's two-way and that it's checking the specific calendar your events live on. A common failure mode is a one-way ICS feed dressed up to look like full sync — bookings land on your calendar, but your existing events never protect your time.

How to connect a Google or Outlook calendar

If your calendar is Google or Microsoft, you're on the easy path. Both expose a proper API, so schedulers can do real-time, two-way sync. The flow is nearly identical everywhere:

In the scheduling app, open Availability → Calendar settings (or Integrations).
Click Connect calendar account and pick Google or Outlook / Microsoft 365.
Sign in and grant the requested permissions.
Choose which calendars to check for conflicts (read) and which calendar new bookings should be added to (write).
Save.

That's it. Bookings now appear instantly, and your existing events block your availability. Calendly, for instance, connects natively to Google, Outlook/Office 365, and Exchange this way (Calendly Help).

If you keep several calendars — work Google, personal Google, a shared team calendar — connect all of them as "check for conflicts" sources but pick a single one as the booking destination. Otherwise new bookings scatter across calendars and you lose track of them.

The Apple Calendar problem (and the iCloud workaround)

Here's the catch for Mac and iPhone users. Apple Calendar has no public API. Unlike Google and Microsoft, Apple doesn't offer a hosted way for third-party apps to read and write your iCloud calendar in real time. Schedulers can only reach iCloud through CalDAV, an older sync protocol, or a one-way ICS subscription feed.

It got worse in 2024: Calendly removed the ability to connect an iCloud calendar on August 20, 2024 (Calendly). If your availability lived in Apple Calendar, that integration simply stopped.

You have three realistic options:

Bridge through Google. If your events sync to a Google account that you also view inside Apple Calendar, connect the scheduler to the Google account instead of iCloud. The scheduler reads Google (with full two-way sync); you keep using Apple Calendar as your viewer. This is the cleanest workaround for the Calendly-style tools.
Use a scheduler that still supports iCloud via CalDAV. Some tools (Cal.com, Acuity, and others) still connect to Apple Calendar through CalDAV. Expect slower refresh — minutes, not seconds — and check whether it's true two-way sync or a one-way feed.
Subscribe to a one-way ICS feed. As a fallback, many schedulers publish an ICS link you can add to Apple Calendar so bookings appear there. Just know this is one-way: it won't block your booking page from your Apple events.

If the CalDAV-vs-API distinction matters to your setup, I went deep on the tradeoffs in Google Calendar API vs CalDAV — the short version is that API-based sync is faster and more reliable, which is exactly why the iCloud-only path feels laggy.

CalDAV itself is built on the open iCalendar standard (RFC 5545), the same .ics format used to share events across Google, Outlook, Apple, and basically every calendar app (iCalendar, Wikipedia). That portability is great for moving an event around; it's just not a substitute for real-time two-way sync.

Why your scheduler isn't blocking busy times

You connected your calendar, but people can still book you during meetings. This is the most common sync complaint, and it's almost always one of two fixes.

1. Your events are marked "Free," not "Busy." Calendars let each event carry an availability status. Most schedulers only treat Busy events as conflicts — a Free event won't block anything (Calendly). All-day events default to Free in a lot of calendars, which is why "I'm out all day" events famously fail to block bookings. Open the offending event and switch it to Busy.

2. The calendar isn't selected as a conflict source. Connecting an account isn't the same as telling the scheduler to check that specific calendar. Go back to calendar settings and confirm every calendar that holds real commitments is ticked under "check for conflicts." A secondary or shared calendar is easy to miss here.

A couple of other usual suspects: sync delay (CalDAV and ICS feeds refresh on a timer, often every 5–15 minutes, so a just-added event may not block yet), and time-zone mismatches between your calendar and your scheduler.

A cleaner setup: one calendar as the source of truth

The reason calendar sync gets messy is usually fragmentation — work events in Google, personal in iCloud, a side project in Outlook — with a scheduler trying to read across all of it. Every extra connection is another place sync can quietly break.

The setup that holds up: pick one calendar account as your source of truth, route everything into it, and point your scheduler at that single account. On a Mac, that means using a fast, native calendar that sits on top of a real API rather than juggling browser tabs and laggy CalDAV feeds. That's the whole idea behind hora — a native Mac calendar built directly on the Google Calendar API, so what you see is what your scheduler sees, in near real time. I wrote about getting that sync to feel instant in Real-time Google Calendar sync on macOS, and about why a native app beats a web wrapper for this in Best Fantastical Alternative for Google Calendar Users.

You don't need a fancy stack. You need one calendar that's reliably synced, marked Busy where it matters, and connected to your scheduler as a conflict source. Get those three right and double-bookings basically stop.

FAQ

Does Calendly work with Apple Calendar?

Not directly anymore. Calendly removed iCloud calendar connections on August 20, 2024. The common workaround is to connect Calendly to a Google account that your events also sync to, and keep viewing that calendar in the Apple Calendar app.

What's the difference between one-way and two-way calendar sync?

One-way sync sends data in a single direction — usually bookings onto your calendar — but doesn't read your existing events to block availability. Two-way sync does both: bookings appear on your calendar and your calendar events block your booking page, which is what prevents double-bookings.

Why isn't my scheduling app blocking out busy times?

Most often the conflicting events are marked "Free" instead of "Busy," so the scheduler ignores them — switch them to Busy. The other common cause is that the calendar holding those events isn't selected as a "check for conflicts" source in your scheduler's settings.

How long does calendar sync take?

Google and Outlook connections sync in near real time because they use push-based APIs. Apple Calendar and other CalDAV or ICS-based connections refresh on a timer, often every 5–15 minutes, so a newly added event may take a few minutes to block your availability.

Will syncing show my private event details on my booking page?

No. Schedulers read your events only to mark slots as busy; they show the time as unavailable, not the title or details. Your private event content stays private to your calendar.

If this saved you from a few double-bookings, it did its job.

Follow the build at @moto_szama, check out hora Calendar, or reach out at hello@horacal.app.