Calendar sync tools compared
A calendar sync tool copies events from one calendar account onto another and keeps the copies current, so every calendar shows the same busy times.
Keeper.sh is a calendar sync service that copies events between Google Calendar, Outlook, iCloud, Fastmail and any CalDAV server, so every calendar shows you as busy at the same times. It is free for 2 calendar accounts and 3 connections, and Pro is $5 a month for unlimited calendars.
The blog has step-by-step guides for syncing Google Calendar, Outlook and iCloud with each other, and for syncing Fastmail, Nextcloud, Proton, Zoho or Radicale with one of them. Calendar sync guides
How the tools compare on price, free plan and speed
Figures for other tools come from each tool's own website, linked beside them, and were checked on 10 November 2026.
| Tool | Entry price | Free plan | Calendars | Update speed |
|---|---|---|---|---|
| Keeper.sh | $5/month, or $45/yearkeeper.sh/pricing | Yes: 2 calendar accounts and 3 connections, no card neededkeeper.sh/pricing | Google Calendar, Outlook, iCloud, Fastmail, any CalDAV server; .ics links read-onlykeeper.sh/features | Pro: Google and Outlook within seconds, iCloud, Fastmail and CalDAV every minute. Free: every 30 minuteskeeper.sh/docs/plans-and-limits |
| SyncDate | $10/month billed yearlysyncdate.app | Yes: 2 accounts, 2 calendars, 1 sync, copies 30 days aheadsyncdate.app | Google Calendar, Outlook, iCloud, Fastmail, Nextcloud, any CalDAV server; ICS links read-onlysyncdate.app | Google and Outlook "Usually in under a minute"; iCloud and CalDAV "Checked about every 15 minutes"syncdate.app |
| OneCal | $5/user/month billed annually, 2 calendarsonecal.io | No: 14-day trial, no cardonecal.io | Google Calendar, Outlook, iCloud, any CalDAV serveronecal.io | "in real-time", no figure published; iCloud and CalDAV up to 10 minutesonecal.io |
| CalendarBridge | $5/month, or $4/month billed yearlycalendarbridge.com | No: 7-day trial, no cardcalendarbridge.com | Google Calendar, Microsoft 365 for Business, Microsoft personal accounts, iCloud; .ics linkscalendarbridge.com | Google and Outlook in real time; iCloud and .ics links every 5 to 10 minuteshelp.calendarbridge.com |
| SyncThemCalendars | $3.99/month billed yearly, or $4.99/month, 5 calendar syncssyncthemcalendars.com | No: 14-day trial, no cardsyncthemcalendars.com | Google Calendar, Outlook, iCloudsyncthemcalendars.com | "in real time", no figure publishedsyncthemcalendars.com |
| Kalender Sync | €5/month, or €50/yearkalender-sync.de | Yes: 2 calendar accounts and 1 sharing with another personkalender-sync.de | Google Calendar, Outlook, iCloud, GMX, WEB.DE, Posteo, mailbox.org, STRATO, Disroot, Infomaniak kSuite; iCal feeds read-onlykalender-sync.de | Google and Outlook by webhook; iCloud about every 5 minuteskalender-sync.de |
| CalendarSync | $5/month, or $50/yearunicala.io | Yes: 2 calendar accounts, 1 sync configuration, 1 scheduling linkunicala.io | Google Calendar, Outlook, iCloudunicala.io | "Changes propagate instantly via webhooks", no figure publishedunicala.io |
| Reclaim.ai | $10/seat/month billed yearlyreclaim.ai | Yes: Lite, with 1 Calendar Syncreclaim.ai | Google Calendar and Outlookhelp.reclaim.ai | "in real-time", no figure publishedreclaim.ai |
| OGCS | Freeoutlookgooglecalendarsync.com | Yes: the whole app is freeoutlookgooglecalendarsync.com | Outlook and Google Calendaroutlookgooglecalendarsync.com | Every 15 minutes at the fastest; Outlook edits within 2 minutes with push turned onoutlookgooglecalendarsync.com |
All nine tools on one page
Calendar sync services
SyncDate alternative
SyncDate Plus is $10 a month billed yearly for 5 accounts. Keeper.sh Pro is $5 a month for unlimited calendars, and every copy hides the event's details by default.
OneCal alternative
OneCal has no free plan and starts at $5 per user a month, billed yearly, for 2 calendars. Keeper.sh is free for 2 calendar accounts, and Pro is $5 a month for unlimited calendars.
CalendarBridge alternative
CalendarBridge's plans are $5 to $40 a month, billed monthly, after a 7-day trial. Keeper.sh is free for 2 calendar accounts, and Pro is $5 a month for unlimited calendars.
SyncThemCalendars alternative
SyncThemCalendars syncs Google Calendar, Outlook and iCloud from $4.99 a month, or $3.99 a month billed yearly, after a 14-day trial. Keeper.sh adds Fastmail and CalDAV, and is free for 2 calendar accounts.
Kalender Sync alternative
Billed monthly, Kalender Sync is €5 a month for 3 calendar accounts and €12 a month for unlimited. Keeper.sh Pro is $5 a month for unlimited calendars, and connects Fastmail and any CalDAV server.
SyncGene alternative
SyncGene's free plan syncs by hand once a month. Keeper.sh's Free plan syncs 2 calendar accounts every 30 minutes without a click.
Calendar apps and planners that also sync
Morgen alternative
Morgen is a calendar and planning app whose blocking workflow runs daily at 6pm, or when you run it by hand. Keeper.sh copies busy time between calendars through the day, free for 2 calendar accounts.
Reclaim.ai alternative
Reclaim.ai's Calendar Sync covers Google Calendar and Outlook. Keeper.sh also syncs iCloud, Fastmail and CalDAV calendars, free for 2 accounts and $5 a month on Pro.
Notion Calendar alternative
Notion Calendar is a free calendar app with a blocking feature. Keeper.sh syncs Google Calendar, Outlook, iCloud, Fastmail and CalDAV calendars in whichever app you already use.
Booking tools used with calendar sync
How to stop Calendly double-booking
Calendly only blocks time on the calendars it checks for conflicts. Connect the missing calendar, or have Keeper.sh copy its events as busy blocks onto one Calendly already checks.
Calendly with Keeper.sh
Calendly checks 1 calendar on its Free plan and up to 6 on paid plans. Keeper.sh copies the rest onto a calendar Calendly already checks, so you keep your booking links.
Desktop and automation tools
OGCS alternative
Outlook Google Calendar Sync is a free Windows app that syncs while the PC runs it. Keeper.sh syncs from its own servers, free for 2 calendar accounts.
Zapier alternative for calendar sync
A Zap creates an event when another event appears, and each one uses a task. Keeper.sh keeps every copy current, with no task count, free for 2 calendar accounts.
Prices and head-to-head comparisons
CalendarBridge pricing explained
CalendarBridge's three plans differ by synced connections: 2, 20 and 56. Five calendars that all show each other need 20 connections, which is Premium.
OneCal vs CalendarBridge
OneCal starts at $5 per user a month billed annually and connects any CalDAV server. CalendarBridge starts at $4 a month billed yearly and signs a HIPAA BAA.