Why Does Syncing Your Calendars Require Another Company Knowing Your Schedule?

Christoph Gockel · May 2026

I have three calendars. One personal, one for my company and one with a client who gave me an Office 365 account. For a long time, I thought that was just how it works. You accumulate calendars the way you accumulate email addresses.

The trouble started when company meetings kept overlapping with client meetings. Neither calendar knew about the other, so I'd get double-booked in both directions. I'd have to reschedule, apologise and wonder why something this simple was so hard to get right.

If you have more than one calendar, you probably know this feeling. A meeting gets scheduled because your team can only see one of your calendars. A personal commitment gets steamrolled because nobody knew it existed. You end up manually cross-checking calendars before accepting anything, which works until you forget. And we always forget eventually.

Looking for a fix

When I went looking for a solution, I found plenty of sync services. Most of them work the same way: you sign in with your Google account, your Microsoft account, your Apple account. You give the service permission to read and write to your calendars. Then their servers pull your events, figure out the overlaps and push placeholder events back.

It sounds reasonable. And it works. The sync happens, the double-bookings stop and you can get on with your day.

I was about to sign up for one of these services when I paused on the permissions screen. It was asking for full read and write access to every calendar on my Google account. Every event. Every attendee. Every location. Every note I'd ever added to a calendar entry.

What your calendar actually knows about you

Think about what's in your calendar for a moment. Not just the meetings. The doctor visits. The school pickups. The therapy sessions. The job interviews you haven't told anyone about yet. The recurring lunch meeting that tells anyone paying attention who you spend your time with.

Your calendar is one of the most detailed records of your daily life. It knows where you'll be, when you'll be there and often who you'll be with. It's more revealing than most people realise.

And when you use a SaaS sync service, all of that goes to a company's servers. Not just your data. If your calendar has meetings with clients, colleagues or patients, their names, email addresses and meeting details go along for the ride. You might be comfortable sharing your own schedule with a third party. However, your clients and colleagues never agreed to that.

A question worth asking

I'm not suggesting these services are careless with your data. Many of them have solid security practices and clear privacy policies. The question isn't whether they'll misuse your data. The question is whether another company needs access to your schedule at all.

Calendar sync is a straightforward problem. You have events in one place, and you want a copy of them in another place. Both places already exist on your computer. Your Mac already has access to all your calendars through its built-in Internet Accounts. The events are already right there.

So why give another company access just to move them around?

Sync without adding another company to the mix

On-device sync takes a different approach. Instead of giving a new service access to your calendars, it reads your events directly from your Mac's calendar store and creates the placeholder events right there on the same machine. No additional company gets access to your schedule.

This works because macOS already knows about all your calendars. When you add a Google account or a Microsoft account in System Settings, your Mac downloads those events and keeps them up to date. A local sync app simply works with what's already there.

The result is the same: your work calendar shows when you're busy with personal things, and your personal calendar shows when you're in meetings. The difference is that no additional company needs access to make it happen. Google and Microsoft still sync your calendars as they always do. No new party gets added to that chain.

What about your clients?

This is the part that really made me think. If you're a consultant, freelancer or anyone who works with clients, your calendar contains their information too. Meeting titles, project names, participant lists. When you hand all of that to a sync service, you're making a decision about your clients' data on their behalf.

With on-device sync, that question goes away. No additional company gets access to their data. There's no new service to disclose in your privacy policy, and no extra place where their information could show up in case of a data breach.

Why I built Very Good Calendar Sync

This is exactly why I built Very Good Calendar Sync. I wanted a sync that worked well and didn't require me to trust a third party with my entire schedule.

It runs on your Mac and uses the calendars you already have set up. There's no account to create, no credentials to hand over and no additional service that gets access to your schedule.

You set up your syncs once and it runs quietly in the menu bar. Whenever your calendars change, it picks up the new events and creates the corresponding blockers automatically. You can filter by day of the week or time of day, so you only sync what matters during work hours.

Because it runs on your Mac, it only syncs while your Mac is awake. If you need your calendars to stay in sync around the clock, even when your computer is off, a cloud-based service will be a better fit. See how it compares to OneCal or CalendarBridge.

Your first sync is free, no payment required. If it solves the problem for you, plans start at £1.99/month.

If you're tired of double-bookings and don't want to give another company access to your schedule, give it a try.

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