Summary
Connect Google and Outlook in Keeper.sh and send busy-block copies each way: Google onto the Outlook calendar a colleague actually books against, Outlook onto the Google calendar they actually check. Two ticks, two mappings. Copies land while the laptop is shut.
Work Outlook + personal Google, or the reverse. A colleague using Scheduling Assistant or Find a time must see the other calendar’s hours as taken. If they only need to add Google Calendar to Outlook as a visible overlay in the grid, that is /blog/add-google-calendar-to-outlook — Secret address plus Subscribe from web. Stop there if overlay is the whole job.
The weakest link is that Outlook Add calendar / Subscribe from web / classic From Internet is a read-only feed on Microsoft’s clock. Google From URL / Make available to public is a pull-only overlay. An .ics import is a snapshot. Outlook Google Calendar Sync (OGCS) can write both ways, but only while that Windows PC stays on.
Keeper.sh exists to write private copies (placeholder title from the source calendar) onto the calendar that stays empty. On Pro, a change on Google or Outlook shows up on the other calendar the moment you make it. Nothing of theirs has to stay awake.
Subscribe, From URL, import, and OGCS fail that leftover job; the numbered Keeper.sh setup does not.
Outlook Add calendar is a read-only feed
A dentist runs a clinic calendar on personal Google. A colleague using Outlook Scheduling Assistant sees that hour as free and books it. Overlay does not fix this: a subscribed feed is not a first-class Outlook appointment. The reverse is the same job: work hours on Outlook, personal Google still showing the slot open.
Forum proof backs this up. A Microsoft Tech Community reply marked as solution on 4 Jun 2025 says subscribed .ics events “Do not show up in Scheduling Assistant availability” and “Do not mark you as 'busy' for others.” Same reply: “What Won’t Work: Subscribing via an .ics feed… Importing a static .ics file… Viewing a calendar in ‘overlay’ mode — it shows up visually but does not influence your free/busy availability” (Microsoft Tech Community). Slipstick’s Bowen, on 11 Jun 2026, describes work Exchange plus personal Google, using ICS into “Add a calendar from the Internet,” and writes “updates take forever to sync I missed a meeting because of this last week.” Chandler replies, “It only provides a read-only calendar and updates can be delayed by several hours.” (Slipstick).
Microsoft’s path for overlay is clear. On 29 Aug 2026, View your Google Calendar in Outlook says:
“Below the calendar grid on the left, select Add calendar, then select Subscribe from web.”
“Paste the copied URL into the address bar, then select Import.”
Google’s side, from Sync your calendar with computer programs, fetched 29 Aug 2026:
“If your calendar application doesn't have a full sync option, or if you want a read-only view of one calendar, you can sync your calendar to the application using a link to iCal.”
“In the "Secret address in iCal format" section, copy the link.”
“Important: Only you should know the Secret Address for your calendar. Do not share this address with other people.”
Microsoft’s refresh guidance in Import or subscribe to a calendar in Outlook.com or Outlook on the web, fetched 29 Aug 2026:
“When you subscribe to a calendar, your calendar will automatically refresh if the other calendar is updated. This can sometimes take more than 24 hours.”
“This update can take more than 24 hours, although updates should happen approximately every 3 hours.”
And from Calendar sharing in Microsoft 365, fetched 29 Aug 2026:
“If the recipient is an Outlook.com user, the sync will happen approximately every three hours.”
“If the recipient is in Gmail.com, the calendar might be updated every 24-48 hours.”
Classic Outlook readers still name this From Internet. Microsoft’s current View your Google Calendar page does not print that label (checked 29 Aug 2026). If overlay was the whole job, stop at /blog/add-google-calendar-to-outlook.
Verdict: Add calendar / Subscribe from web (and classic From Internet) is a read-only overlay on Microsoft’s clock. It does not mark you busy for a colleague, and it does not write back.
Google From URL and publish are pull-only
The reverse native path is the same limitation. Paste an Outlook ICS into Google with From URL, or publish Google so Outlook can subscribe. Both are pull-only.
Google’s Subscribe to someone else’s calendar, fetched 29 Aug 2026:
“To subscribe to a new calendar, you must use a computer web browser. You can't subscribe to a calendar in the Google Calendar app for Android, iPhone, or iPad.”
“Important: You can only add a calendar with a link if the other person's calendar is public.”
“On the left, next to "Other calendars," click Add other calendars From URL.”
“Enter the URL of the published calendar.”
“Click Add calendar.”
“The calendar displays on the left, under "Other calendars."”
And Create & manage a public Google calendar, fetched 29 Aug 2026:
“Under "Access permissions for events," check the box next to "Make available to public."”
“If you don't want other people to read the details of your events, select See only free/busy (hide details).”
“To share a calendar that can be accessed in iOS: Click Integrate calendar copy the link in "Public address in iCal format." The iCal address only works if the calendar is public.”
Google publishes no refresh interval for a URL-added calendar.
/docs/accounts-and-calendars: “A calendar subscribed from a link is read-only, so it can send events but never receive them.”
Verdict: From URL / Make available to public overlays a read-only feed, and only if the source is public. It is not a copy onto the calendar a colleague books against.
Importing an .ics file is a snapshot
Microsoft’s classic path, from the same View your Google Calendar in Outlook page under the Classic Outlook tab, fetched 29 Aug 2026:
“In classic Outlook, select File > Open & Export > Import/Export.”
“In the Import and Export wizard, select Import an iCalendar (.ics) or vCalendar file (.vcs), then select Next.”
“Select Open as New.”
“The imported calendar is a static snapshot; it does not self-update. To update it, you need to subscribe to it (as described above) or repeat this procedure later to import a copy of the most current version of your calendar in Google Calendar.”
Also at the top of that page:
“By importing a snapshot of your Google calendar into Outlook, you can see it alongside other calendars in the Outlook Calendar View.”
“If you don't, the only way to update it will be to import another, more current snapshot.”
From Import or subscribe to a calendar in Outlook.com or Outlook on the web, fetched 29 Aug 2026:
“When you import an .ics file, you get a snapshot of the events in the calendar at the time of import. Your calendar doesn't refresh the imported events automatically -- even if the calendar's owner makes an update.”
Verdict: Import is a one-time snapshot. It never updates itself and it never becomes a live copy.
OGCS only runs while the PC is on
Outlook Google Calendar Sync, or OGCS, is a Windows desktop app, not a Google or Microsoft built-in. Its FAQ (OGCS FAQs, page last edited 13 Jan 2025; fetched 29 Aug 2026) says:
“Granted, it would be nice for OGCS not to need installing on a PC that is powered on for it to sync.”
“scheduled syncs are restricted to a maximum frequency of 15 minutes, or 120 minutes if Push Sync is also enabled.”
“Push Sync triggers an automatic sync within 2 minutes of any calendar change within Outlook.”
“From its origin, OGCS has been focused on users who are sat behind a corporate firewall connecting to Exchange accounts and want to sync out to Google.”
OGCS is Outlook ↔ Google on a Windows machine. It does not host itself, run on Mac, or sync iCloud.
Verdict: OGCS can write both ways, but only while that Windows PC is powered on. It is not unattended when the laptop is shut. Keeper.sh does not replace OGCS for air-gapped Exchange; it replaces it when the PC cannot stay on.
Put busy blocks on both calendars with Keeper.sh
You need a Keeper.sh account. Connecting copies nothing by itself. /docs/accounts-and-calendars: “Connecting copies nothing by itself. Events only move once you send them to another calendar.” Busy-block both ways is two mappings.
- Sign in to Keeper.sh and connect Google through the Google permission screen. Connecting copies nothing.
- Connect Outlook through the Microsoft permission screen. Two accounts is the Free allowance.
- Open the Google calendar page. Under Send Events to Calendars, tick the Outlook calendar. One connection, Google → Outlook. Copies are real Outlook events. /docs/sending-events-to-another-calendar: “Each calendar you tick becomes one connection. Events are copied into it, one way, and the copies are kept corrected as the originals change.”
- Open the Outlook calendar page. Tick the Google calendar. Second connection, Outlook → Google. That is two of Free’s three connections.
- Leave the privacy defaults. Copies use a placeholder title from the source calendar; description and location stay hidden. Those toggles are Pro. Guest lists are never copied. See /docs/what-a-copied-event-shows.
- Confirm on each destination: a real event, named after the source calendar, no notes, no location, no guest list. Wait for the next write.
A create still lands on the calendar that owns the event. If nothing arrives, see /guides/event-has-not-arrived. If the same event appears twice, see /guides/same-event-appears-twice. Untick stops new copies; already-copied events stay (/docs/sending-events-to-another-calendar: “Untick the calendar in Send Events to Calendars and new events stop being copied. Events already copied stay where they are.”). If a password or admin revokes the connection, re-auth at /docs/accounts-and-calendars.
A pasted share, ICS, or subscribe link is not a destination. If you connected a URL instead of signing in, you can send from it, not into it.
Sources are read every minute on every plan. Free destinations write every 30 minutes. Pro writes every minute; on Pro, a change on Google or Outlook shows up on the other calendar the moment you make it. Free includes 2 accounts, 3 connections, and 1 shareable link. Pro is $5/month or $45/year (/docs/plans-and-limits: “Pro is $5 a month, or $45 a year paid annually.”). Guest lists are never copied, on any plan.
Recipes: /recipes/sync-work-and-personal-calendars and /recipes/keep-personal-details-out-of-work.
Why a Keeper.sh copy instead of a feed or a PC left on
- Add calendar / Subscribe from web / From Internet only overlaid a read-only feed. A Keeper.sh connection writes a private copy onto the calendar that stayed empty.
- An
.icsimport was a snapshot. Keeper.sh copies are kept corrected as the originals change. - OGCS stopped when the Windows PC slept. On Pro, a change shows up on the other calendar the moment you make it, while the laptop is shut.