How to sync multiple calendars: setup guide

One calendar is easy. Three calendars take real effort to keep straight. If you want to sync multiple calendars so you stop getting double-booked, here's the short version:

1. Viewing is not blocking. Overlaying your calendars lets you see all your events. Syncing them lets other people see when you're actually free.
2. The built-in tools have limits. Calendar subscriptions in Google and Outlook can take hours to update, and they don't block your time for anyone else.
3. Keep the details private. Your boss should see "Busy," not "Therapy Appointment."
4. Use a sync tool like Caltsu for real-time blocking. Connect all your Google and Outlook accounts and it blocks your busy time across all of them.

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You have a work calendar in Outlook, a personal calendar in Google, and maybe a shared family calendar in iCloud.

Each one is tidy on its own. None of them know about the others.

So you accept a meeting on your work calendar because the slot looked empty, and your personal calendar has a dentist appointment at the same time.

Here's how to connect them properly.

Why syncing multiple calendars is harder than syncing two

Syncing two calendars, from A to B, is simple. Events go one way.

With a third or fourth calendar, every calendar has to reflect busy time from every other one. That's a lot more connections to keep right.

Get the setup wrong and you'll run into:

• Privacy leaks. Clients see the details of your personal doctor's appointments.
• The "zombie" loop. An event syncs from calendar A to B, then from B back to A, and the copies keep multiplying.
• Slow updates. You cancel a meeting on one calendar, and another still shows you as busy three hours later.

A good sync tool handles all of this for you.

Common multi-calendar scenarios

Most people who sync multiple calendars fit one of these three setups.

The "double agent" (work and personal)

Your job runs on Microsoft 365 and your personal life runs on Google or iCloud. Coworkers need to know you're unavailable during your kid's school play, but company policy or plain privacy keeps your personal events off the work calendar.

The freelancer or consultant

Three clients have each given you an email address on their domain. That's three calendars, and Client A keeps booking you over Client B's meetings because neither can see the other's schedule.

The family manager

You run a work calendar, a shared calendar with your partner and a calendar for your kids' activities. You have to look at all three just to find a free hour.

Option 1: the built-in sync (limited)

Google and Outlook can show one calendar inside another for free. The catch is that it's read-only.

You see all your schedules in one place. Your scheduling tools, like Outlook's "Find a Time," don't.

How to do it (syncing a Google calendar to an Outlook calendar):

1. Open Google Calendar on your computer.
2. Go to Settings and sharing for the calendar you want to share.
3. Scroll down to the Secret address in iCal format and copy the URL.
4. Open Outlook on the Web.
5. Choose Add Calendar > Subscribe from web.
6. Paste the URL and give it a name.

This only creates an overlay. You see your Google events in Outlook, but when a coworker tries to book you, that slot still looks free to them.

These subscriptions also refresh on the provider's schedule, which can mean hours of delay. For a busy week, that's too slow.

Option 2: third-party sync tools

To block your time across platforms, you need a dedicated sync tool. It copies busy slots from one calendar to the others as they happen.

That's the only way a meeting booked on Calendar A immediately blocks the same time on Calendars B and C.

Why Caltsu works for multi-calendar syncing

We built Caltsu for exactly this. Unlike the built-in options, Caltsu syncs both ways across every calendar you add to a sync.

• It blocks your time for real. Caltsu creates placeholder events on your other calendars, so scheduling tools like Calendly or Outlook's Scheduling Assistant see you as busy.
• It keeps details private. Blocks never carry the event's title, attendees, location, notes or meeting link. Your "Client strategy session" on Calendar A shows up as "Busy" on Calendar B.
• It's fast. Google and Microsoft send Caltsu push notifications when something changes, so blocks update within seconds, not once a day.

Step by step: how to set up a multi-calendar sync with Caltsu

1. Connect your accounts

Sign up for Caltsu and give it permission to access each calendar provider.

• Connect your primary Google Calendar.
• Connect your work Outlook/Office 365 account.
• Apple iCloud is not supported yet. If you use Apple Calendar, keep the events you want synced in a Google calendar.

2. Create your sync

Add every calendar you want to keep aligned to one sync. Caltsu syncs both ways, so each calendar gets a block for events on the others. A meeting booked on Client A's calendar blocks that time on Client B's calendar and on your personal calendar.

3. Decide which calendars to include

More calendars in the sync isn't automatically better. Every extra one adds blocks to the others.

Worth syncing:

• Calendars with fixed meetings, like video calls and client reviews.
• Calendars with deep work blocks, if you actually keep them.
• Calendars with travel time.

Better left out:

• Task calendars. If you use a calendar as a to-do list, you don't want every 15-minute task blocking time on your boss's view of your week. Keep tasks on a calendar that isn't in the sync.
• Holiday calendars. Most calendar apps already have a built-in holiday calendar. Syncing a "US Holidays" calendar into accounts that already show US holidays just creates duplicates.

Privacy settings for your multi-calendar sync

For most people this is the main worry. You want to show when you're busy, not what you're doing.

Caltsu never copies the event's title, attendees, location, notes or meeting link. Each block carries the start and end time, a title, Busy by default, and the note "Blocked time from" followed by the source calendar's name.

Tip: You can change the block title. Blocks from your personal calendar could show up as "Personal commitment" on your work calendar, which reads as professional and still reveals nothing.

How to troubleshoot your multi-calendar sync

These are the problems people hit most often.

The infinite loop

Calendar A syncs to B, B syncs back to A, and each side treats the copy as a new event.

Caltsu recognizes its own blocks and doesn't sync them back. If you're running the built-in sync and a third-party tool at the same time, turn the built-in one off. Use one method.

The "ghost" event

You deleted a meeting from your Google calendar, but it still blocks time on your Outlook calendar.

Check how often your sync updates. A subscribed iCal feed can take hours to drop a canceled event. Caltsu removes the block as soon as Google or Microsoft notifies it of the change.

Duplicate entries

You see the same meeting twice on your phone.

You're probably showing both the source calendar and the destination calendar in your phone's calendar app. Hide one of them. You don't need the original and the copy side by side.

Get all your calendars in sync

You shouldn't need three apps to answer "Are you free next Tuesday at 2 PM?"

Once busy time flows between all your calendars, any one of them answers that question correctly. Connect your accounts, put them in one sync, and check the first week of blocks to make sure the right calendars are included.