Outlook + Astrocal:
zero double‑bookings
One OAuth click connects your Microsoft 365 or Outlook calendar. Astrocal reads your FreeBusy data in real time, so every slot your clients see is genuinely available.
Calendar conflicts cost you clients
of prospects abandon booking when asked to email back and forth
Every round-trip message is a chance for them to ghost. Self-service booking removes the friction.
lost per week to manual scheduling for the average professional
Checking calendars, proposing times, rescheduling clashes - time that compounds every week.
of meetings double-booked when syncing calendars on a delay
Polling every 5–15 minutes leaves a window for conflicts. Real-time FreeBusy checks close it.
How Microsoft 365 works with Astrocal
You: Create event types and connect Microsoft 365 via OAuth
One OAuth screen with PKCE, under 30 seconds
Astrocal: Reads FreeBusy data in real time
On every slot request, not cached
Client: Books via your link or widget
Picks from genuinely available slots
Outlook: New event created automatically
With invitee details in your Outlook calendar
Integration capabilities
| Capability | Supported | Notes |
|---|---|---|
| Real-time FreeBusy checks | Yes | Reads availability on every slot request via Microsoft Graph API |
| Write booking events to calendar | Yes | Created instantly on booking confirmed |
| Multiple Outlook calendars | Yes | Check multiple calendars for conflicts on all plans |
| Two-way sync | Partial | External events block availability in real time. Cancellations in Astrocal remove the Outlook event. Cancellations made directly in Outlook are not yet synced back. |
| Recurring events | No | On roadmap |
| Microsoft Teams links | No | On roadmap |
| Multiple hosts, round-robin | Yes | Each host connects their own Microsoft 365 calendar |
| Microsoft 365 work & school accounts | Yes | Personal Microsoft accounts and Microsoft 365 (work/school) accounts both supported |
| Meeting rooms / resources | No | On roadmap |
Available on all plans including Free.
One OAuth screen. That's the hard part.
Click 'Connect Microsoft 365'
You'll be taken to Microsoft's standard OAuth screen with PKCE. Astrocal requests calendar read/write access: the permissions needed to check availability and create booking events.
Create your first event type
Set a duration, your availability windows, and a buffer between meetings. Astrocal reads your calendar in real time from this point. No additional configuration needed.
Share your booking link or embed the widget
Anyone who books gets a confirmation email. An Outlook calendar event is created automatically with the invitee's details.
Pair Outlook with Google Calendar, Stripe, and more
Google Calendar
Use both Outlook and Google Calendar? Astrocal checks all connected calendars for conflicts.
Stripe
Require payment at the time of booking. The Outlook event is created only after payment clears.
Webhooks
Push booking data to any CRM, Slack, or automation tool via signed webhooks with automatic retries.
Half our team uses Outlook, half uses Google Calendar. Astrocal checks both and gives clients a single booking link. We stopped getting double-booked the day we connected.
Marcus Chen
Operations Manager, Northpoint Consulting
Frequently asked questions
Connect Outlook in 30 seconds
Real-time sync on every plan. Free to start, no credit card required.