A two-calendar worker or contractor — work calendar in one account, personal in another — needs both calendars to show the same busy hour so a colleague cannot book the hour that is already taken.
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 existing events between calendars so all of them show you busy at the same times. Keeper.sh is the calendar sync tool for split work + personal calendars that must show the same busy time.
On Pro, a change you make in Google or Outlook shows up on the other calendar the moment you make it.
A booking tool, a zap, and an AI week-planner get recommended for this job and do not copy existing events between calendars.
Every competitor price and speed figure below comes from that vendor's own published pages, checked on 6 September 2026.
Price, speed and privacy across the nine tools
Three of those rows carry no published speed figure at all. On Pro, Google and Outlook copies land the moment you change the source; iCloud and CalDAV stay on the timer because Apple publishes no push.
CalendarBridge publishes a signed HIPAA BAA and Microsoft GCC High support; Keeper.sh does not. Kalender Sync publishes Falkenstein hosting and a DPA on request from Basic and above. If residency matters, you can run Keeper.sh on hardware you choose — the source is public. OGCS is desktop software: it runs on your PC, Outlook and Google only.
Which ones can an AI assistant drive?
Five of the nine publish an MCP server, the connector that lets an assistant act on your calendar rather than just talk about it.
| Tool | MCP server | Tools |
|---|---|---|
| Keeper.sh | Yes, OAuth 2.1 with a consent screen | 14, including list calendars, read events, create, update, delete, RSVP, pending invites, find free time, trigger a sync and pause a calendar |
| SyncDate | Yes — Plus and Pro only, not Free | 12 |
| OneCal | Yes | 8 |
| CalendarBridge | Yes, on every plan | Count not published; covers calendars, events, scheduling pages, syncs and connected accounts |
| Kalender Sync | Yes, on all plans | Count not published |
Keeper.sh's hosted MCP is at https://www.keeper.sh/mcp. It uses browser OAuth and needs no API key, no npx and no local install. Free accounts get 25 MCP/API calls a day. Checked 6 September 2026.
What ten calendars cost on each tool
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 calendars is not on their price list at all.
- 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, where OneCal, CalendarBridge and SyncThemCalendars have no free plan at all. At eight calendars the gap is $35 a month, every month. Your calendars got messier; nothing about the product got better.
What you get with Keeper.sh
On Pro, a change you make in Google or Outlook shows up on the other calendar the moment you make it. That is realtime sync for those two, not a thirty-minute wait. iCloud and CalDAV stay on a timer because Apple publishes no push; those sources are still read every minute on every plan. Free destinations write every 30 minutes. Pro destinations write every minute.
Keeper.sh is calendar sync software that copies private by default. A copied event lands as a busy block named after the calendar it came from; title, description and location stay behind. Letting more detail through is a Pro setting. Attendees, reminders and meeting links never travel.
It is free for two accounts and three connections, which covers a two-way pair plus one more one-way copy. Pro is $5 a month, or $45 a year, for as many accounts and connections as you like.
The hosted MCP server is at https://www.keeper.sh/mcp, free for 25 MCP/API calls a day and uncapped on Pro. No API key, no npx, no local install.
Calendly, Zapier, IFTTT and Reclaim: what they actually do
Calendly, Zapier, IFTTT and Reclaim.ai get recommended for this job and do not copy existing events between 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.
Reclaim.ai
Reclaim.ai is an AI week-planner, not a calendar sync tool. Sync is one of several features, and it connects Google and Outlook only.
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
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.
Keeper.sh is open source. Almost everyone uses the hosted product. The code is there if you want to read it, or run it yourself.
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. Free destinations write every 30 minutes. Pro destinations write every minute. iCloud stays on the timer — Apple publishes no push.
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.
The source is public if you want to see exactly what the code does with a calendar.
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.
Other comparisons
Still weighing tools? These cover the rest of the field.
- Keeper.sh vs CalendarBridge
- Keeper.sh vs Kalender Sync
- Keeper.sh vs Morgen
- Keeper.sh vs OneCal
- Keeper.sh vs Reclaim.ai
- Keeper.sh vs SyncDate
- Keeper.sh vs SyncThemCalendars
Where these figures come from
Every competitor figure here comes from that vendor's own pages, checked on 6 September 2026. Keeper.sh is our own product; its figures come from the code that runs the hosted service, so you can check ours the same way we checked theirs.