For two or more Google accounts, SYNCDATE is the one we recommend: two-way or one-way between accounts, a Busy-only privacy mode (new syncs copy events as Busy; a two-way Mirror between calendars you own keeps the real titles; you can change either before you start), free for 2 accounts and 1 sync, up to 5 accounts on Plus and 20 on Pro. We make SYNCDATE, so weigh this as our view; the other tools below were checked on 8 October 2026.
Native Google Calendar sharing and overlays show your calendars together, but they do not copy an event from one account into another, so they do not mark you busy where a colleague or client is looking. Copying needs a sync tool. Each entry below says what that tool is best for, using only what its own page says on 8 October 2026.
The tools, in order
- SYNCDATE: two-way or one-way, Busy-only mode, free for 2 accounts
- 2calendars: Google only, real-time, one flat monthly price
- Keeper.sh: one-way copies, open source, several providers
- SyncThemCalendars: Google, Outlook and iCloud, one-way or both ways
- OneCal: Google, Outlook and iCloud, 14-day trial, per-user pricing
- CalendarBridge: Google, Microsoft and iCloud, 14-day trial
1. SYNCDATE
Best for: people with two or more Google accounts (work, personal, a client) who want other accounts to see only that they are busy. SYNCDATE copies events between accounts two-way or one-way, and can show copies as plain Busy blocks. New syncs copy events as Busy. A two-way Mirror between calendars you own keeps the real titles. You can change either before you start. It also connects Outlook, iCloud and CalDAV accounts if you add one later. The free plan covers 2 accounts, 2 calendars and 1 sync with no credit card. Plus allows up to 5 accounts, 5 syncs and 4 calendars in one two-way Mirror. Pro allows up to 20 accounts, 20 syncs and 5 calendars in one Mirror, and lets each destination show a different level of detail. We make SYNCDATE, so this entry is our view; see current prices and the full limits.
2. 2calendars
Best for: Google-to-Google sync only, with a flat monthly price. Checked 8 October 2026 on 2calendars.app: the page says it "mirrors events between your Google Calendars in real time", mentions no other provider, syncs both ways by default and can be set to one way, and says "Connect as many Google accounts as you need". Mirrored events show as Busy unless you change that. The plans are measured in sync connections: Free is "1 sync connection, forever free", Pro is $7 a month for up to 6, and Business is $19 a month for up to 40, with a 14-day trial on the paid plans. If every account you have is Google, it is a straightforward choice; if one of them is Outlook or iCloud, its page does not cover that.
3. Keeper.sh
Best for: people who want an open-source, self-hostable tool and are happy with one-way copies. Checked 8 October 2026 on keeper.sh: the page says it is open source under AGPL-3.0 and that "the copying runs one way". You sign in directly with Google, Outlook, iCloud or Fastmail, or paste a calendar link for others. A copy shows the name of the calendar it came from, with no title, description, location or guest list; Pro can include the title, description and location. Free is $0 for up to 2 linked accounts and 3 connections, updating every 30 minutes. Pro is $5 a month with unlimited accounts and connections, and Google and Outlook update within seconds. If you need changes to flow both ways between accounts, the page does not describe that.
4. SyncThemCalendars
Best for: a paid tool that mixes Google, Outlook and iCloud and lets you choose the direction. Checked 8 October 2026 on syncthemcalendars.com: the page says you can sync "across any combination" of Google Calendar, Outlook / Office 365 and Apple Calendar (iCloud), and choose to "mirror events both ways, or only copy from one to another". It lets you hide the details of any field in the copied event. Every plan has a 14-day free trial with no credit card, then Basic is $3.99 a month billed yearly for 5 calendar syncs, Premium $7.99 for 16 and Professional $17.99 for 36, each for 1 user.
5. OneCal
Best for: a paid tool across Google, Outlook and iCloud when you want several one-way or multi-way syncs. Checked 8 October 2026 on onecal.io: the pricing page lists "One-way & multi-way calendar sync" and Google Calendar, Outlook, iCloud Calendar and CalDAV, though the home page labels CalDAV "Coming Soon". It says you can control the level of detail shown, including excluding event titles. There is a 14-day trial with no credit card and no free plan after it. Prices are per user per month billed annually: Starter $5 for 2 calendars, Essential $10 for 5 and Premium $25 for 50.
6. CalendarBridge
Best for: people whose calendars include Microsoft 365 or iCloud and who want a choice of detail level. Checked 8 October 2026 on calendarbridge.com: the page lists Google Calendar, Microsoft 365 for Business, Microsoft personal accounts, iCloud and .ics links. It says Google and Microsoft calendars sync "typically within a minute or two" and iCloud and .ics every 5 to 10 minutes, and that you choose what is shared, "from simple busy blocks to full event details". It offers a trial with no credit card and no free plan. On the pricing page, yearly billing is $4 a month for 2 calendars, $8 for 5 and $32 for 8. The page does not say whether sync is one-way or two-way.
Which one to pick
If every account is Google and you only need a simple mirror, 2calendars and SYNCDATE both fit; check the plan limits against your account count. If one account is Outlook or iCloud, look at SYNCDATE, SyncThemCalendars, OneCal or CalendarBridge. If you want to self-host or only need one-way Busy copies, look at Keeper. Whichever you choose, create a test event in each account and check what the other accounts show before you rely on it. For a wider comparison, see free Google Calendar sync tools and the calendar sync comparison.
How to set it up with SYNCDATE
First decide where events need to appear. If you just want to see your week, a native overlay may be enough. Collecting client events into one personal calendar needs a one-way Push. Every account showing your availability needs one two-way Mirror.
| Job | Arrangement | What it does not do |
|---|---|---|
| See several calendars together | Native calendar overlay or unified view | Does not create event copies in each account |
| Collect client events in one calendar | One Push: multiple sources to one hub | Does not send hub copies back to the client calendars |
| Let each calendar receive the others' events | One Mirror containing all writable calendars | Does not remove plan limits, filters or provider delays |
Several client calendars into one personal hub. Connect the accounts you are allowed to access, open the client-calendar hub recipe, select the client calendars as sources and one personal calendar as the destination, then check the appearance settings: the recipe keeps original titles, so use a private hub or change that setting if others can read it. Start the sync and verify a test event from each source.
Shared availability across work, personal and client accounts. Connect the accounts and confirm write access to each calendar, open the multi-account Mirror recipe, select all calendars in one Mirror, choose Busy titles unless every destination may see details (a two-way Mirror between calendars you own keeps original titles by default), then check that a harmless event created in each calendar reaches the others, including edits and deletion.
Telling the copies apart. When several calendars feed one, a custom title that starts with the source calendar's name shows where each copy came from, on every plan. See Label synced events with the calendar they came from.
Do not chain separate syncs. With A to B and B to C, a copy arriving in B is not passed on to C. Use one larger Mirror instead, and read the known limitations before changing an existing setup. For a work and personal pair, see the personal-to-work recipe.
Which SYNCDATE plan fits?
| Limit | Free | Plus | Pro |
|---|---|---|---|
| Connected accounts | 2 | 5 | 20 |
| Syncs | 1 | 5 | 20 |
| Calendars across syncs | 2 | 20 | 100 |
| Calendars in one Mirror | 2 | 4 | 5 |
| Calendars in one Push | 2 | 10 | 20 |
| Forward window | 30 days | 1 year | Unlimited |
| Different appearance per destination in one sync | No | No | Yes |
Count both sources and destinations. One Google account can contain several calendars; account limits and calendar limits are separate. A Push's complexity also depends on the number of sources and targets.
For five calendars, Pro is needed if all five must mirror each other. Plus may fit a one-way arrangement of four sources and one hub, provided the account and complexity limits fit. Choose based on direction, not just the number five.
See current prices and the complete limits. Team provides Pro limits per seat with shared billing; it does not raise the per-Mirror cap.
If copies are missing or colleagues still book over you
Check selected calendars, write access, direction, filters, the sync window and any dashboard error. Provider delays and retries can affect arrival times. Avoid running a second tool on the same calendars as a repair, because it can create duplicate copies. For booking problems, follow the double-booking checks. If one account is Microsoft, choose the Google and Outlook method first; two Microsoft accounts have their own Outlook setup guide. For iCloud, see the iCloud guide.
Frequently asked questions
Can I sync two Google accounts for free?
Yes. The Free plan covers 2 connected accounts, 2 calendars and 1 sync, with no credit card, which is enough for one work and one personal Google account in a single sync. A third account needs Plus, which allows up to 5 accounts; Pro allows up to 20. See the free plan and current prices.
How many syncs do I need for three calendars?
One Mirror can contain all three writable calendars on Plus or above. If only one calendar needs the others' events, use one Push with two sources and one destination. Separate pairs do not relay copies onward.
Can I sync five Google Calendars on Plus?
Plus can fit some five-calendar Push arrangements, such as four sources into one hub, subject to account and complexity limits. A five-calendar Mirror requires Pro. Plus's total allowance of 20 calendars is not a per-Mirror allowance.
What if I add a sixth calendar?
Check the arrangement before connecting it. Standard Pro allows five calendars in one Mirror. A six-calendar Push may fit, but copies only flow from its sources to its targets; it is not a substitute for every calendar sharing availability with every other.
Can I keep client names private?
Use Busy titles and exclude descriptions, locations and guests, then inspect a test copy. The client-hub recipe keeps original titles by default. Different appearance per destination in one sync requires Pro.
Does seeing all calendars together prevent double-bookings?
Not by itself. Confirm which calendars your booking tool checks and whether the relevant events are marked Busy. A combined view and copied availability are different things.