Proton Calendar end-to-end encrypts the parts that give your day away, the event title, description, location, and who is invited so Proton cannot read them; only the start and end times stay readable so it can fire reminders. The web app is open source and independently audited, the Android app went open source in 2025, and the whole thing shares one login with Proton Mail and Drive. As with Tuta, the encryption means no CalDAV: you can import and export .ics files but not sync live with outside apps. Choose it if you are already on Proton, or want an encrypted suite more than broad interoperability.
Proton Calendar
Encrypted calendar that comes with a Proton account.
proton.me
FreemiumOpen SourceE2E EncryptedAccepts CryptoWindowsmacOSLinuxAndroidiOSWebSwitzerland
Pricing Free plan with up to three calendars; paid plans (Mail Plus, or the Unlimited bundle around €9.99/mo) raise that to 25.
Strengths
- Event details encrypted end-to-end
- Open-source, independently audited web app
- Shares one account with Proton Mail and Drive
- Bitcoin accepted through account credit
Considerations
- No CalDAV; .ics import and export only
- Best inside the Proton ecosystem
Listed in Calendars
