Glossary
Two-Way Sync
Two-way (bidirectional) sync mirrors changes in both directions. An event created or edited on either calendar is reflected on the other within minutes.
How two-way sync works
When you enable two-way sync between calendar A and calendar B, the sync engine watches both for changes. A new event on A creates a mirror on B; a delete on A removes the mirror on B; an edit propagates either direction. Each mirrored event carries an internal identifier so the engine knows which events belong together.
Conflict resolution
Two-way sync needs a rule for what happens when both sides change the same event in the same window. The standard approach is last-write-wins by updated timestamp. SyncCal uses that default and surfaces a warning when it detects a conflict so you can review.
When to prefer one-way sync
If one calendar is the system of record (for example, your work Outlook calendar) and the other is downstream (for example, the Google calendar Calendly watches), one-way sync is safer. There is no chance an accidental edit on the downstream calendar propagates back.
What gets mirrored
Title, start and end times, location, attendees (optional), description (optional), free/busy status. Reminders, attachments, and platform-specific extensions like Google’s color labels are not mirrored.
In context
Two-way sync is the right default for iCloud-to-Outlook setups where you genuinely edit on both sides. One-way is the right default for Calendly conflict mirroring, where the destination calendar exists only so the booking tool sees the truth.
For troubleshooting when two-way sync stops working, see Why is my calendar not syncing.