Encrypted Calendar Sync in 2026: Comparing Your Options

Here's the good news: in 2026, there are multiple services that offer some form of encrypted calendar sync. Five years ago, you could count them on one finger. The space has grown.

The bad news? Most of these options are incomplete, locked into a specific ecosystem, or simply abandoned. If you've spent any time trying to find a proper encrypted replacement for Google Calendar, you know the frustration. Things look promising on the surface, then you dig in and find deal-breaking limitations.

We wanted to write an honest comparison. Not a marketing piece where we trash the competition and declare ourselves the winner. Just a clear-eyed look at what exists, what works, and what doesn't.

Proton Calendar

Proton Calendar is the most well-known option. It's end-to-end encrypted and comes bundled with Proton Mail. If you're already paying for Proton Unlimited, you get it included. The encryption is real. Proton cannot read your events. That matters.

But Proton Calendar has significant limitations for anyone who wants calendar sync as a standalone tool. There's no CalDAV support, which means you can't use it with third-party calendar apps. You are limited to Proton's own web app and mobile apps. No desktop client. No integration with the calendar tools you might already use.

Contacts sync? Only within Proton's own apps. Tasks? Not supported. It's a calendar and only a calendar, tightly bound to the Proton ecosystem. If you live entirely inside Proton, this works fine. If you don't, you'll hit walls quickly.

Tuta Calendar

Tuta (formerly Tutanota) offers encrypted calendar as part of their email service. Like Proton, the encryption is genuine. Your events are encrypted before they reach Tuta's servers.

The limitations are similar to Proton's. No CalDAV. No third-party app support. Calendar sharing is limited. No contacts or tasks sync outside their own app. Tuta has built a solid encrypted email product, but their calendar remains a secondary feature with a narrow scope.

Both Proton and Tuta deserve credit for shipping encrypted calendars at all. Most companies never even try. But both treat the calendar as an add-on to email rather than a first-class product.

EteSync

EteSync was the original. It did exactly what many of us wanted: end-to-end encrypted sync for calendars, contacts, and tasks using the Etebase protocol. The protocol is genuinely well-designed. Zero-knowledge architecture, proper key management, conflict resolution, offline support. The cryptographic foundations are sound.

The problem is that EteSync stopped being maintained. The apps haven't been updated. The server codebase stagnated. The Android app still works for some users, but it's not receiving fixes or improvements. The web client is outdated. For a tool that handles your daily schedule, “it still kind of works” isn't good enough.

This is actually where SilentSuite comes from. We forked EteSync because the protocol deserved a maintained product around it. More on that below.

Nextcloud with E2EE

Nextcloud is the go-to self-hosted solution for a lot of privacy-conscious users, and understandably so. It supports CalDAV, which means you can use it with almost any calendar app. The ecosystem is huge. You own the server.

Here's the nuance people often miss about Nextcloud and encryption: Nextcloud does offer end-to-end encryption for files. It does not offer E2EE for calendar or contacts data. Your events are stored in plaintext in the database on whichever server runs Nextcloud.

If you self-host Nextcloud yourself, on a box only you can access, that's actually a pretty solid privacy story. Nobody else has the keys to the building, so nobody else gets to read the events sitting in the database. For a lot of people, that's good enough.

Where it gets shakier is the hosted Nextcloud route, where a third party runs the server for you. Now “in plaintext on the server” means in plaintext on their server. A breach, a rogue admin, a misconfigured backup, or a legal request, and your calendar is readable. The CalDAV protocol and the underlying database simply weren't designed for E2EE.

This isn't a criticism of Nextcloud. They're solving a different problem and doing it well. But we see people assume that “Nextcloud + E2EE” means everything is encrypted, and that's only true if you also happen to control the server it runs on.

Skiff: a cautionary tale

Worth mentioning briefly: Skiff offered encrypted calendar (alongside email and documents) and looked promising. Then Notion acquired them in early 2024 and shut the whole thing down. Users had six months to export their data and move on.

This is the risk with VC-funded privacy tools. The incentives don't always align with long-term operation. When the acquirer doesn't care about your encrypted calendar product, it just disappears. Something to consider when choosing where to put your trust.

SilentSuite

This is what we're building. We should be transparent about our bias here: this is our project, and we obviously believe in it. But we'll try to be straightforward about what we offer and where we currently stand.

SilentSuite is a fork of EteSync, built on the Etebase protocol. Full end-to-end encryption for calendars, contacts, and tasks. The server never sees your data in plaintext. Our code is open source under AGPL-3.0. Servers are hosted on GDPR-compliant EU infrastructure.

We offer a paid hosted service (because that's how you sustain a product without selling data) and a self-host option for people who want full control. The Etebase protocol means your data isn't locked into our service. You can export it. You can run your own server.

Honestly, we're still early. We don't have feature parity with Google Calendar and we're not pretending to. What we do have is a working encrypted sync layer, active development, and a clear roadmap. We're building the client apps now.

Comparison table

Here's how everything stacks up. We've tried to be fair. If we've gotten something wrong, let us know.

	Proton	Tuta	EteSync	Nextcloud	SilentSuite
E2EE calendar	Yes	Yes	Yes	No	Yes
E2EE contacts	Partial	Partial	Yes	No	Yes
E2EE tasks	No	No	Yes	No	Yes
CalDAV support	No	No	Via bridge	Yes	Yes*
Mobile apps	Yes	Yes	Outdated	Via 3rd party	Yes*
Web app	Yes	Yes	Outdated	Yes	Yes
Self-hostable	No	No	Yes	Yes	Yes
Open source	Partial	Yes	Yes	Yes	Yes (AGPL-3.0)
Status	Active	Active	Abandoned	Active	Active
Price	Free / from €4/mo	Free / from €3/mo	Was €2/mo	Self-host cost	From €3/mo

“Partial” for Proton/Tuta contacts means encrypted contacts exist within their own apps, but there's no sync protocol you can use with external clients.

* SilentSuite: Android is native, CalDAV works through our standalone bridge for Apple Calendar and Thunderbird, and iOS still works with the original EteSync app since we share the Etebase protocol.

The honest take

If you're already in the Proton ecosystem, Proton Calendar is a reasonable choice. Same goes for Tuta. They're real companies with real encryption, and for many users the walled-garden trade-off is acceptable. You get a working encrypted calendar as part of a bundle you're already paying for. That's not nothing.

But if you want encrypted sync for calendars, contacts, and tasks, with open-source code you can audit, a protocol you can self-host, and no lock-in to a specific email provider? The options are thin. EteSync proved the concept and then went quiet. Nextcloud doesn't encrypt PIM data. Skiff got acquired out of existence.

That gap is exactly why SilentSuite exists. We took a proven protocol from a project that stalled and are building a maintained, sustainable product around it. Not because the other options are bad, but because none of them do the specific thing we needed.

What we're asking

If encrypted calendar sync matters to you, get started with SilentSuite. It helps us understand demand, plan capacity, and prioritize features.

We'll send you one email when the beta opens. That's it. No newsletter spam. No growth-hack drip campaigns.

Your schedule, your contacts, your tasks. Encrypted. Open source. Yours.