Quick answer: Compare these tools by the calendars you need to connect, the copies each destination should receive and who will operate the service. Keeper offers hosted and self-hosted options. SYNCDATE is hosted, with one-way and two-way arrangements and controls over copied fields. Both can suit calendar copying; a generic push-versus-polling claim does not distinguish them accurately.
We make SYNCDATE. The vendor facts below come from Keeper's own pages checked October 18, 2026; we have not run a comparative provider benchmark. An earlier version of this comparison said Keeper only used fixed polling. Its current product pages describe provider notifications on Pro, so that contrast has been removed.
What Keeper currently publishes
Keeper's site names Google Calendar, Outlook, iCloud and Fastmail. Hosted Free lists two linked accounts, three connections and 30-minute updates. Pro describes push notifications for Google/Outlook and timer-based CalDAV updates within a minute. It also offers configurable copied details and agent/API access.
Its self-hosting page describes AGPL-3.0 code and paid sync features without hosted plan limits. You supply infrastructure and Google/Microsoft OAuth applications. This is a separate operating commitment, not the hosted Free tier. Check Keeper's current plans and setup documentation for your exact arrangement.
What to check in SYNCDATE
SYNCDATE connects Google, Outlook and writable CalDAV calendars, including iCloud, Fastmail and Nextcloud. An iCal feed is a read-only source. A Push copies originals in one direction; a Mirror lets originals from either side travel to the other. Separate syncs do not relay copied events onward.
Free covers two accounts, two calendars and one sync, with a 30-day forward window. Several calendars sharing availability need one Mirror containing those calendars: Plus allows up to four in one Mirror and Pro up to five. A total-calendar allowance is not the size of a single Mirror. For a consolidated view without copying back, use a one-way hub instead. Check current plan requirements.
Google and Outlook changes usually reach the other calendar in under a minute. CalDAV and iCal are polled about every 15 minutes on all plans. Google/Outlook fallback polling is separate: paid plans use 15 minutes; Free uses two hours with a live push channel or one hour without it. Notifications, provider limits and retries can add delay. These are configured behaviors and published expectations, not a measured speed contest against Keeper.
Decide what each destination may show
New SYNCDATE syncs copy events as Busy. A two-way Mirror between calendars you own keeps the real titles. You can change either before you start. Review Description, Location, Guests, Privacy and Free or busy independently; a title does not certify availability or field omission after you change the settings.
Use the personal-to-work recipe when work should receive masked personal copies. If one destination needs real titles and another needs masked copies within the same sync, review the per-destination appearance requirement before choosing a plan. Appearance settings explain the controls.
For either tool, ask which account can read the resulting copies and which calendar the booking tool or Scheduling Assistant actually checks. A combined view does not prove that another account contains a copy or shows you as unavailable.
Hosted service or your own installation
Choose a hosted service when you want the vendor to operate it. Choose self-hosting when you are prepared to maintain the installation, credentials, upgrades, backups and monitoring. Account-connection policies still apply: running your own server does not grant permission to connect an employer's accounts.
Then compare the exact units each plan counts: linked accounts, calendars, connections or syncs. Similar-looking totals can describe different arrangements. List your original calendars, direction, required destination fields and forward window before comparing the plans. A useful Free setup can be enough; paying is appropriate when a specific supported requirement exceeds it.
Verify before replacing a working setup
Test with separate non-sensitive calendars where possible. Create a harmless Busy event, inspect its actual destination copy, move it and check cleanup after deletion. For a two-way arrangement, repeat from the other calendar. Check the Scheduling Assistant or booking tool against the destination, not an overlay of the source.
Before switching the production pair, record the old service's cleanup behavior and stop it writing to that pair. Inspect retained copies before enabling another writer; do not bulk-delete events merely because they look similar. Removing old Busy copies can temporarily reopen availability, so plan the handover and keep the originals safe. Cancel the old subscription through its separate vendor procedure only after the replacement is verified.
There is no universal migration time or guaranteed conflict-free switch. For a Google–Outlook arrangement, use the method-choice guide; for several accounts, review one multi-account Mirror.
Frequently asked questions
Does Keeper only use scheduled polling?
No. Its current site describes provider notifications for Google and Outlook on Pro, and timer-based checks for CalDAV. Hosted Free lists 30-minute updates. Check the current plan and provider rather than applying one timing figure to every setup.
Is self-hosting the same as a hosted free plan?
No. Self-hosting means operating the service and its infrastructure yourself. Compare that responsibility separately from the account and connection limits of a vendor-operated Free plan.
Can a Busy title still leave time bookable?
Yes. Title and Free/Busy are separate properties. Inspect the actual destination event and confirm that the scheduling surface checks that calendar.