You have a Google Calendar and you need it to show up somewhere else — another account, Outlook, or a second view. If both Google accounts have to hold real events, that is How to Sync Google Calendars Between Two Accounts. Google and Outlook is How to Sync Google Calendar with Outlook. This page is which Google screen does which job, and when you need copies.
Who is this for?
Someone who needs to know which of those jobs they actually have. If you only need both calendars on one screen, a share or a subscribe is enough. If another account, a colleague, or a booking tool has to see the time as taken, you need events written into that calendar.
What does Google mean by sharing or subscribing?
Sharing grants another person permission to look at, or edit, the same calendar. It does not create a second event they own. Google: they get an email, and “To find your calendar, they need to click the link in the email.” Permissions — See only free/busy, See all event details, Make changes — still apply to your calendar. A work or school administrator can block it.
On a computer: My calendars → More → Settings and sharing → Shared with → Add people and groups → Send.
Caption: Settings and sharing → Shared with → Add people and groups.
Subscribe to calendar adds someone else’s Google calendar under Other calendars after they approve. Google says it then “shows under Other calendars.” Computer only: “To subscribe to a new calendar, you must use a computer web browser.” From URL is in the same menu. Google: “You can only add a calendar with a link if the other person's calendar is public.”
Caption: Other calendars menu → Subscribe to calendar and From URL.
Subscribe to someone else’s calendar. Google does not publish how often a URL-added calendar is re-read.
Secret address in iCal format (Settings → the calendar → Integrate calendar) is how you view your calendar in other applications. Google: “The Secret Address lets you view your calendar in other applications.” “If you want to let someone else view your calendar, you can share your calendar.” “You should not give your Secret Address to other people.” If the other application is Outlook, the full path is How to Sync Google Calendar with Outlook.
Caption: Integrate calendar → Secret address in iCal format.
Share your calendar with someone.
Share grants access to the same calendar. Subscribe to calendar and From URL overlay it. The secret address is view-only in other apps.
Why doesn’t Import & Export keep two calendars in sync?
Google: “Imported events don't stay in sync between your 2 accounts. If you want your calendars to sync, share your calendar with the other account.” You can transfer events from a different calendar application or Google Account. Guests and conference data are not imported. It is a one-time dump, not an ongoing write.
Settings → Import & Export → Select file from your computer.
Caption: Import & Export.
Import events to Google Calendar.
Import & Export transfers events once. It does not keep two calendars in sync.
When is an overlay enough?
When you are the audience. Share, subscribe, or add the second account in the Google Calendar app if you only need both calendars on one screen while you plan. Nothing else — Find a time, a booking page, a colleague — is reading the other account for those times.
How do you copy events out of Google Calendar?
Connect the Google account and the destination account to Keeper.sh. On the source calendar, under Send Events to Calendars, tick the calendar that should receive copies. Each tick is one direction. Two-way is two connections.
Copies are private by default: titled after the source calendar, description and location hidden unless you turn each on (Pro). Sources are read every minute. Free writes every 30 minutes. Pro writes every minute, and Google notifies Keeper.sh on change. Free is 2 accounts and 3 connections. Pro is $5 a month or $45 a year.
Two Google accounts specifically: How to Sync Google Calendars Between Two Accounts. Outlook: How to Sync Google Calendar with Outlook. Dashboard detail: Docs and Guides.
Caption: Keeper: Send Events to Calendars ticked toward the destination.