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Proton Calendar vs Microsoft Outlook: catalog facts
Proton Calendar	Microsoft Outlook
Freemium Free account available, with paid Proton plans and a business version.	Freemium Free app and account available; Microsoft 365 plans add paid features and Office apps.
Android, iOS, Web	Windows, macOS, Android, iOS, Web
End-to-end encryption of event details Built-in scheduling for booking meetings	Email, calendar and contacts for multiple accounts in one app Available on desktop, mobile and web
Requires a Proton account Works best within the Proton ecosystem	Closed source and tied to Microsoft services Some features, including Copilot, require a paid plan
Downloadable app, Web application, Hosted service	Downloadable app, Web application
Closed source	Closed source
License not stated	License not stated
Account needed	Not stated if an account is needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked September 23, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.