Best Calendar Sync Tools: 9 Compared on Price, Speed and Privacy

You accept a meeting in one calendar. The other still shows you free. Someone takes that hour, and now you owe two people the same 2pm.

A calendar sync tool copies your events between calendars so all of them show you busy at the same times. Nine tools do that job. Three more get recommended for it constantly and do something else.

Every competitor price and speed figure on this page comes from that vendor's own published pages, checked on 11 August 2026.

Keeper.sh is free with two accounts and three connections, and $5 flat at thirty calendars. Three quieter questions decide whether you are still happy in a year:

• Where do your event titles, locations and attendee names end up?
• What does this cost once you have ten calendars instead of two?
• What happens to your synced calendars the day the vendor is acquired or switched off?

Which calendar sync tool should you use?

• Most people should start with Keeper.sh. Connect your work Google and your personal iCloud, sync them both ways, and add one more one-way copy on top. That is free, permanently, with no card and no clock.
• Keeping your event titles to yourself — Keeper.sh. A calendar you connect starts stripped: Keeper.sh writes a block of busy time carrying the calendar's name, and leaves the title, the description and the location behind. Detail is a Pro setting you switch on, not one you switch off.
• Your iCloud calendar, read every minute — Keeper.sh. Keeper.sh reads yours every minute on every plan, and on Pro the block is on your other calendar about a minute later, two at the outside. CalendarBridge publishes 5–10 minutes and OneCal up to 10.
• HIPAA with a signed BAA today, or Microsoft GCC High — CalendarBridge. Nothing else in this category touches GCC High. That flank costs $40 a month for eight calendars, on US cloud only, with no CalDAV and no way to run it yourself.
• An AI to rearrange your week — Reclaim.ai, and it is good at that. Sync there is one of eight features and rate-limited by tier. It connects Google and Outlook only — no iCloud, no CalDAV, on any plan.
• A signed data processing agreement and German hosting before you can buy — Kalender Sync. It publishes Falkenstein databases, a signed GDPR agreement and named subprocessors, from €4 a month. Keeper.sh answers differently: self-host and the database sits on your own hardware, in your own country.

Connect two accounts free. There is no clock on it and no card at the end.

Price, speed and privacy across all nine tools

Four of those rows carry no published speed figure at all. Keeper.sh reads every calendar every minute, iCloud and CalDAV included.

Which ones can an AI assistant drive?

Three of the nine publish an MCP server, the connector that lets an assistant like Claude or ChatGPT act on your calendar rather than just talk about it.

Keeper.sh's is free at 25 calls a day and uncapped on Pro, and the REST API behind it does the same things from a script. Checked 11 August 2026.

Ten calendars: $5 here, $40 for eight at CalendarBridge

OneCal, CalendarBridge and SyncThemCalendars all charge by the calendar or by the sync pair. The price goes up in proportion to how bad your problem is. A contractor with nine client calendars plus a personal one is the worst case, and a common one.

• CalendarBridge — $40 a month, the top published tier, covering eight calendars. Ten is a conversation.
• OneCal — $25 a month per user billed annually, the tier that stretches to 50. Six accounts already moves you off the $5 plan.
• SyncThemCalendars — $3.99 a month for five sync pairs, $7.99 for sixteen, $17.99 for thirty-six. The meter is pairs, so the bill tracks how tangled your calendars are.
• Keeper.sh — $5 a month, flat. Ten calendars, thirty calendars, as many connections as you want.

At two connected accounts Keeper.sh is free outright. OneCal, CalendarBridge and SyncThemCalendars have no free plan. At eight calendars the gap is $35 a month, every month, for a problem that got worse rather than a product that got better.

Start with two accounts, free — the $5 tier is there when you outgrow it, at any number of calendars.

What each calendar sync tool is like to use

Keeper.sh

Keeper.sh is for anyone whose calendars live in more than one place and who does not want their meeting titles copied onto a server they cannot read or run.

It is free for two linked accounts and three connections, and Pro is $5 a month for as many as you like. Keeper.sh reads every connected calendar every minute on both plans. On Pro the copy lands about a minute later, two at the outside; on free it is about fifteen minutes, thirty-one at the very worst.

Setting up takes three decisions. Sign in with Google or Microsoft, or use an app-specific password for iCloud and Fastmail, which lets Keeper.sh in without handing over your main password. Then pick which calendar feeds which, and pick the direction.

What arrives is a block of busy time named after the calendar it came from. Title, description and location stay behind, and letting more through is a Pro setting. Attendees, reminders and meeting links never travel at all.

Cancel a meeting and the copy goes with it. Keeper.sh keeps a record of every copy it wrote so it can take that copy back, and it never deletes an event it did not create.

It works with Google, Outlook, iCloud, Fastmail, and any other calendar that uses the CalDAV standard. Read-only calendar links work too, so the conference feed and the university timetable block time against work like everything else.

Keeper.sh also ships an MCP server with 14 tools, so an assistant like Claude can list your calendars, read events, and create, move, cancel or RSVP to them. The same actions are in the REST API. Both are free at 25 calls a day and uncapped on Pro.

The code is AGPL-3.0 on GitHub, with seven published Docker images, including a standalone container that brings up the whole stack. The version you can run yourself is the version that runs the hosted service. Start on the hosted version — same engine, none of the upkeep.

SyncDate

SyncDate is the one to look at if you want a hosted service run from European data centres. It publishes about four seconds on Google and Outlook, with a 15-minute backup check, at $8.99 a month. It runs in Hetzner data centres in Germany and Finland and offers a self-serve data processing agreement, all checked 11 August 2026.

The trade-off — $8.99 a month against Keeper.sh's $5 flat at any number of calendars. Keeper.sh's stripped busy block is more than a policy: the code that does it is AGPL-3.0, so you can read it or run the whole thing on your own server.

OneCal

OneCal is for someone who wants sync, booking links and a unified calendar view billed as one product. It costs $5 per user a month for two calendars, up to $25 for fifty, both billed annually. It advertises "real-time" with no figure attached, and up to 10 minutes for iCloud.

The trade-off — calendars are the meter, so six accounts moves you from $5 to $10 per user, and shared team calendars head toward $25. There is no free plan, only a 14-day trial, and no CalDAV. It says "We don't store any calendar event data" — a promise, with no code to read and no server of yours to keep it on.

CalendarBridge

CalendarBridge is for regulated work. It has been HIPAA compliant since 2022 with a BAA from the Premium plan up, holds SOC 2 Type 1, and supports Microsoft GCC High for government tenants. Nothing else in this category goes there.

Pricing runs $5 a month for two calendars, up to $40 for eight. It publishes within a minute on Google and Outlook, and 5–10 minutes on iCloud.

The trade-off — $40 a month for eight calendars is the most expensive per-calendar price on this page, and the published tiers stop there. Compliance is certificate-based on US cloud: no EU or regional residency, no CalDAV, no self-hosting.

SyncThemCalendars

SyncThemCalendars is for a few sync pairs across a lot of calendars, cheaply. It charges $3.99 a month for five sync pairs, rising to $17.99 for thirty-six, and calendars and events are unlimited. It publishes no speed figure.

The trade-off — pairs are the meter, so the bill grows with how fragmented your calendars are rather than staying flat. There is no free plan, no CalDAV, no calendar links, no team features, and nothing to read or run yourself.

Kalender Sync

Kalender Sync is for a European buyer who has to satisfy a privacy officer before anything gets signed. It publishes databases in Falkenstein, Germany, a signed GDPR data processing agreement and named subprocessors, from €4 a month. It quotes seconds to a few minutes on paid plans, and every 5 minutes for iCloud, and writes anonymised busy blocks by default (checked 11 August 2026).

The trade-off — a data processing agreement is a promise about a server somebody else runs. Self-hosting Keeper.sh puts the database on hardware you choose, in the country you already trust. The code deciding what leaves it is AGPL-3.0 and readable before you sign anything.

Unicala

Unicala is aimed at exactly the buyer Keeper.sh is built for. Its headline is "Sync All Your Calendars. Own Your Data", it advertises self-hosting and "real-time" with no figure published, and pricing is free, then $5, then $6 per seat.

The trade-off — its "Open source" checkmark links to no repository and names no license, checked 11 August 2026. Owning your data is a property of software you can read and run, not a line on a feature grid. Ours is on GitHub under AGPL-3.0, with the Docker images that build it.

Reclaim.ai

Reclaim.ai is for people who want an AI to arrange their week, and it is good at that. Sync is one of eight things it does, at $10 per seat a month, and the free tier gives you one calendar sync. It publishes no speed figure for sync.

The trade-off — it connects Google and Outlook only, which rules it out if anything you own is on iCloud, Fastmail or your own server. Sync is also rate-limited by tier. Reclaim is inside Dropbox now, so what gets built next answers to Dropbox.

OGCS

OGCS is for a Windows user with desktop Outlook installed who wants sync that costs nothing. It is free and open source under MPL-2.0. It syncs every 15 minutes, or every 2 minutes for changes you make in Outlook.

The trade-off — it runs only while your PC is awake and the app is open, it needs desktop Outlook, and there is no iCloud or CalDAV. A Keeper.sh instance you run yourself works from a server instead, and never phones home: no telemetry collector is hardcoded.

Calendly, Zapier and IFTTT: what they actually do

These three come up constantly in answers to "how do I sync two calendars". None of them copies your existing events between your calendars.

Calendly

Calendly is a booking tool. Its own help pages describe the calendar connection precisely: "Calendly checks your calendar for busy times and adds new meetings to it".

That is reading your busy times and writing the meetings it books. The free plan checks one calendar for conflicts, and paid plans cap at six calendar connections per user at every tier, including Enterprise. Keeper.sh does not count your calendars.

Zapier

Zapier says it outright: "Zapier does not support two-way syncing at this time". The same page warns that loops "will repeat the same data over and over".

Repeating events are a documented problem too: "Repeated events in Google Calendar aren't supported with the New Event trigger", and editing a series fires once per occurrence. Its free plan checks every 15 minutes, dropping to 2 minutes on Professional and 1 minute on Team.

IFTTT

IFTTT can create a calendar event. On its Google Calendar service, the only actions are "Quick add event" and "Create a detailed event".

There is no update action and no delete action. An event you move or cancel has no published way to change on the other calendar. The iOS Calendar service has one action and the same gap.

Where calendar sync actually breaks

Most comparison pages stop at price and speed. The things that ruin a synced calendar are elsewhere.

A repeating event is not one event. Your Monday standup is a rule, not fifty meetings, and a tool that treats the series as one item moves all fifty when you move one week. Keeper.sh expands the rule into individual occurrences first, honours the dates you already deleted, and moves only the week you moved.

Daylight saving breaks naive tools. A 9am recurring meeting has to still be 9am after the clocks change. Keeper.sh carries a 140-entry table for Exchange time zone names like "Eastern Standard Time", which Google rejects outright.

Deletions are harder than additions. Cancel a meeting, and a copy that stays behind still blocks you. Keeper.sh keeps a record of every copy it made so it can remove that copy later, and it never touches an event it did not create.

Feeds in the wild are malformed. Conference schedules, university timetables and government holiday feeds all break the standard in small ways. Keeper.sh is regression-tested against ten captured real-world feeds — Google holidays, GOV.UK, Hebcal, Meetup, Stanford, Berkeley, an Exchange export — inside a suite of 1,086 test cases.

The guest list stays behind. Keeper.sh never copies attendees, meeting links or reminders, so the copy blocks the time without re-inviting the room. It does read attendees, so you can accept an invitation from inside Keeper.sh.

None of this is visible when it works, which is the whole job. The long version of why calendar sync is hard is written up separately.

What happens when a calendar sync tool shuts down

This is the question that costs you the most. When a hosted sync tool goes away, you get two problems at once. Nothing is syncing, and every copy it ever made is still sitting on your calendars with nothing left to clean it up.

Reclaim is now inside Dropbox, and several names in the table above did not exist two years ago. A tool whose code you cannot get is one acquisition away from a roadmap written by somebody with different priorities.

Keeper.sh is AGPL-3.0 on GitHub, with seven published Docker images. One is a standalone container that starts the whole stack and runs its own database migrations. If the hosted service disappeared tomorrow, the software would still be there, and it would still run.

Almost everyone should let us run it: a server, a domain, updates, backups and your own Google and Microsoft sign-in apps are real work. Either way you can read exactly what the code does with your calendar before you trust it with one. Start on the hosted version.

Common questions about syncing two calendars

Does Keeper.sh do two-way sync?

Yes, and you build it from two connections, one in each direction. The free plan's three connections cover a two-way pair plus one more one-way copy.

Keeping direction explicit is deliberate: at a glance you know which calendar you edit and which one shows a copy.

Can I sync iCloud with Google Calendar?

Yes. You set it up with an app-specific password from Apple, so Keeper.sh never sees your Apple ID password.

Keeper.sh reads iCloud every minute on every plan, and on Pro the copy lands about a minute later, two at the outside. On free it is about fifteen minutes, thirty-one at the very worst.

Will my colleagues see my private appointments?

Not by default. Keeper.sh replaces the title with the calendar's name and drops the description and location before anything reaches the other calendar. Your dentist appointment arrives as a block of busy time with no detail attached.

Letting more detail through is a Pro setting. So are event filters, and the window Keeper.sh looks at — a month back and two years ahead by default. On the free plan you get the private defaults and cannot change any of them.

Where do my event details actually live?

Keeper.sh reads the whole event to work out when you are busy, and on the hosted service that read sits in our database. What never travels is the detail: titles, descriptions and locations are stripped on the way out by default.

Run Keeper.sh yourself and that database is on your own hardware. The software never phones home, and you can read the code that decides what leaves it.

If I cancel a meeting, does the copy really go away?

Yes. Keeper.sh writes a record the moment it makes a copy, and that record outlives the event, so the copy can still be found and removed. An event Keeper.sh did not create is never touched.

Set up your first calendar sync free

Connect a work calendar and a personal one. The first block of busy time lands on the other calendar with the title stripped. Two accounts and three connections are free, permanently, with no card and no countdown.

Connect two accounts free

Where these figures come from

Every competitor figure here comes from that vendor's own pages and was checked on 11 August 2026. Keeper.sh's own figures come from the code that runs the hosted service, so you can check ours the same way we checked theirs.