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Free calendar sync: a guide to tools and limits

What free calendar sync can do: Google and Outlook sharing, Apple Calendar and iCal links. Where each falls short, and when a paid sync tool is worth it.

5 min readCaltsu Team

On this page7
  1. Overlays vs. true syncing
  2. The best free calendar sync options
  3. iCal links: the free but flawed method
  4. Paid sync tools with a free trial
  5. When you need to upgrade from a free sync
  6. The real cost of a "free" sync
  7. How to choose the right free option for you

Most free ways to sync calendars are view-only overlays. They let you see all your events in one place, but other people still see you as free, so they can still double-book you.

Here's what you can do without paying:

  • Built-in sharing in Google and Outlook. It works, but watch the privacy settings, and cross-platform updates are slow.
  • The Apple Calendar app. Good for seeing every event on your phone. It doesn't block any time on your work calendar.
  • iCal links. The most common free method. Updates can take hours to arrive, which is long enough for a conflict.
  • Caltsu's 14-day free trial. It syncs Google and Outlook calendars within seconds, and you don't need a credit card to start.

You probably already pay for a dozen subscriptions, and adding another just so your work and personal calendars know about each other feels silly.

Free calendar sync is possible. The free options just charge you in other ways: your time, your privacy, and your reputation when you get double-booked.

Below is what you can do for free, how to set it up, and where each method falls short.

Overlays vs. true syncing

There are two different things people call "sync".

An overlay shows several calendars in one view. Only you see the combined schedule. To everyone else, you still look free.

True syncing copies events from one calendar into another as "Busy" blocks, so other people see your real availability.

Most free options are overlays.

The best free calendar sync options

Google Calendar's built-in sharing

Google lets you share a calendar with another Google account. If everything you use is Google, this is one of the better free options.

How to set it up:

  1. Open Google Calendar on your computer.
  2. Hover over your calendar, click the three dots, and choose Settings and sharing.
  3. Under "Share with specific people," add your other email address.
  4. For privacy, choose "See only free/busy (hide details)."

The catch: It only works well between Google accounts. To get the calendar into Outlook you need an iCal link, and those update slowly.

Outlook's built-in sharing

Outlook has a similar free option.

How to set it up:

  1. Open Outlook on the web.
  2. Go to Settings > Calendar > Shared calendars.
  3. Under "Publish a calendar," choose your calendar and the permission level.
  4. Click Publish and copy the ICS link.

Paste that link into another calendar app to get a view-only copy of your Outlook calendar.

The catch: A published Outlook calendar can take hours to update in Google Calendar, and you can get double-booked in the gap.

Apple Calendar on your iPhone or Mac

Apple's Calendar app can show several accounts at once, such as Google, Exchange and iCloud.

How to set it up:

  1. On an iPhone, open Settings > Apps > Calendar > Calendar Accounts. On iOS 17 and earlier it's Settings > Calendar > Accounts. On a Mac, open System Settings > Internet Accounts.
  2. Tap Add Account and sign in to your other accounts.

The catch: This only combines the calendars on your device. Your work calendar still doesn't know about your personal events, so scheduling tools show you as free when you aren't.

Subscribing to a calendar by iCal link works in almost every calendar app and takes a minute to set up. The problem is the refresh rate. The app that subscribes decides when to fetch updates, and Google Calendar can take several hours. You can't force it to refresh sooner. A meeting added this morning may not show up in time to block the slot.

Because the built-in options are slow, several companies sell sync tools. Some have a limited free tier. Others, like Caltsu, have a free trial.

The Caltsu free trial

Caltsu has no free plan. There is one paid plan, and you can try all of it free for 14 days without a credit card. See pricing for the current price. If you don't subscribe after the trial, your existing sync keeps running, but at most every 15 minutes, and you can't add accounts or rules.

Caltsu copies each event into your other calendars as a "Busy" block, so people see you're taken without seeing what you're doing.

  • Source: Your personal calendar (event: "Job interview")
  • Destination: Your work calendar (event: "Busy")

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When you need to upgrade from a free sync

A paid sync tool is worth it if:

  • You use scheduling links. Overlays don't block time for booking tools like Calendly.
  • You need changes to show up fast. iCal feeds can lag by hours.
  • You want to control what others see. Built-in sharing often shows either everything or nothing.

The real cost of a "free" sync

A free sync that misses updates costs you in other ways. Missed meetings, reschedules, and the minutes you spend copying events by hand add up. A sync tool that runs in the background lets you trust the calendar without checking it.

How to choose the right free option for you

  • Your schedule rarely changes: use the built-in sharing in Google or Outlook.
  • You mostly want to see everything on your iPhone: use the Apple Calendar app.
  • Your calendar changes every day and other people book you: use a sync tool like Caltsu, and use the free trial to see if it fits.

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