Proton Calendar

Proton Calendar is a privacy-focused calendar application developed by Proton AG, the Swiss company behind Proton Mail. Built with the same zero-access encryption architecture that made Proton Mail the gold standard for secure email, Proton Calendar ensures that your schedule, event details, and personal information remain completely private—even from Proton itself.

Every aspect of your calendar is encrypted before it leaves your device: event titles, descriptions, locations, and participant lists are all protected with end-to-end encryption. This means that unlike mainstream calendar services that can read your schedule to serve targeted advertising, Proton has no technical ability to access your calendar data. Your meetings, appointments, and personal events stay truly private.

Proton Calendar is headquartered in Geneva, Switzerland, and all data is stored exclusively on servers in Switzerland, Germany, and Norway. This places your calendar under some of the world’s strongest privacy protections, outside the jurisdiction of US surveillance programs and protected by Swiss neutrality. The service is fully GDPR compliant and operates under Switzerland’s Federal Act on Data Protection.

The calendar integrates seamlessly with Proton Mail, allowing you to add events directly from email invitations and send encrypted calendar invites to other Proton users. Native apps for iOS, Android, and web provide cross-device synchronization, while features like customizable reminders, recurring events, and calendar sharing make it a practical replacement for mainstream alternatives.

Key Features

• End-to-End Encryption: All event data encrypted before leaving your device
• Zero-Access Architecture: Proton cannot read your calendar, even with a court order
• Cross-Platform Sync: Web, iOS, and Android apps with seamless synchronization
• Proton Mail Integration: Add events from emails and send encrypted invitations
• Calendar Sharing: Share calendars with family, friends, or colleagues
• Customizable Views: Day, week, and month views with multiple themes including dark mode
• Recurring Events: Daily, weekly, monthly, or custom repeat patterns

Privacy Highlights

Proton Calendar implements the same privacy-by-design principles as Proton Mail. All calendar data is encrypted client-side using OpenPGP, ensuring that event details never exist in readable form on Proton’s servers. The encryption keys are derived from your password and never leave your device.

All servers are wholly owned and operated by Proton, located exclusively in Switzerland, Germany, and Norway under EU/EEA/Swiss jurisdiction. The service collects only the minimum data technically necessary to function, and this metadata is never used for advertising or sold to third parties.

Privacy Breakdown

Data Residency (Score: 100)

Pros:

• All data stored exclusively in Switzerland, Germany, and Norway
• Subject to Swiss FADP and EU GDPR protections
• Outside US and NATO surveillance jurisdiction
• Proton owns and operates all server infrastructure

Cons:

• None identified

Confidence: High — verified through Proton’s transparency reports and infrastructure documentation.

Open Source (Score: 90)

Pros:

• Fully open source code available on GitHub
• Independent security audit by Securitum prior to release
• Active community review and contributions
• Cryptographic libraries (OpenPGP.js) independently audited

Cons:

• Server-side code not fully open source (common for SaaS)

Confidence: High — code publicly available at github.com/ProtonMail.

Privacy Policy (Score: 88)

Pros:

• Clear, comprehensive privacy policy
• Minimal data collection philosophy
• No data used for advertising
• Regular transparency reports published

Cons:

• Some metadata (timestamps, email addresses for shared calendars) technically accessible

Confidence: High — policy reviewed January 2026.

Trackers (Score: 95)

Pros:

• No third-party analytics or advertising trackers
• No tracking pixels in calendar invitations
• Privacy-respecting error reporting only

Cons:

• Basic telemetry for app stability (can be disabled)

Confidence: High — verified through network analysis.

Terms of Service (Score: 65)

Pros:

• Clear service terms
• No broad content licensing claims
• User retains ownership of all data

Cons:

• Standard limitations of liability
• Arbitration clauses present
• Account termination policies could be clearer

Confidence: Medium — ToS reviewed January 2026.