How Much Does Slack Cost? Slack vs Mattermost 2026
How Much Does Slack Actually Cost? The True Price vs Mattermost
Slack's pricing page says $8.75/user/month for Pro. But the real cost? It's higher than you think.
Slack's Real Pricing (2026)
| Plan | Per-User/Month | What You Actually Get |
|---|---|---|
| Free | $0 | 90-day message history, 10 integrations, 1:1 huddles |
| Pro | $8.75 | Full history, unlimited integrations, group huddles |
| Business+ | $15 | SAML SSO, data exports, compliance |
| Enterprise Grid | Custom ($25-35) | Unlimited workspaces, HIPAA, key management |
The Hidden Costs
1. Per-Seat Pricing Adds Up Fast
| Team Size | Slack Pro/Year | Slack Business+/Year |
|---|---|---|
| 10 | $1,050 | $1,800 |
| 25 | $2,625 | $4,500 |
| 50 | $5,250 | $9,000 |
| 100 | $10,500 | $18,000 |
| 250 | $26,250 | $45,000 |
2. Guest Users Still Cost Money
- Single-channel guests on paid plans count as users
- Multi-channel guests count as full users
- External partners and contractors = more seats
3. Storage Limits
- Pro: 10 GB per user
- At 50 users = 500 GB total
- Need more? Upgrade to Business+
4. Compliance and Export
- Message export for compliance: Business+ only ($15/user)
- Data residency: Enterprise Grid only
- HIPAA: Enterprise Grid only
5. Integration Limits on Free
- Free plan: 10 integrations max
- Forces upgrade even for small teams
Mattermost Self-Hosted: The Real Cost
| Component | Monthly Cost |
|---|---|
| VPS (4 GB RAM, Hetzner) | $7 |
| Domain | ~$1 |
| Backups (Backblaze) | $1 |
| Total | $9/month |
What You Get
- Unlimited users
- Unlimited message history
- Unlimited integrations
- Unlimited file storage (limited by disk)
- Full data ownership
- Compliance export built-in
- Self-hosted = full control
Side-by-Side Cost Comparison
| Team Size | Slack Pro/Year | Mattermost Self-Hosted/Year | Annual Savings |
|---|---|---|---|
| 10 | $1,050 | $108 | $942 (90% less) |
| 25 | $2,625 | $108 | $2,517 (96% less) |
| 50 | $5,250 | $156 | $5,094 (97% less) |
| 100 | $10,500 | $192 | $10,308 (98% less) |
| 250 | $26,250 | $300 | $25,950 (99% less) |
What You Give Up
Switching to Mattermost isn't free in non-monetary costs:
| Factor | Slack | Mattermost |
|---|---|---|
| Setup time | 0 (SaaS) | 2-4 hours |
| Maintenance | None | ~1 hour/month |
| Huddles/calls | Built-in | Plugin (Jitsi/BBB) |
| App ecosystem | 2,500+ apps | 100+ plugins |
| Familiarity | Everyone knows Slack | Learning curve |
| Uptime SLA | 99.99% | You manage it |
When Slack Makes Sense
- Teams < 10 (free plan is fine)
- Heavy use of Slack Connect (cross-company channels)
- Need enterprise compliance without in-house DevOps
- Budget isn't a concern
When Mattermost Wins
- Teams > 25 (savings become significant)
- Data sovereignty requirements
- Already have DevOps capability
- Need unlimited history without paying
- Government or regulated industries
The Bottom Line
For a 50-person team, Slack costs $5,250/year (Pro) or $9,000/year (Business+). Mattermost costs $156/year — a 97% reduction.
The real question isn't cost — it's whether your team has the 2-4 hours to set it up and 1 hour/month to maintain it.
Infrastructure and Self-Hosting Costs in Detail
The $9 per month figure in the summary above represents a real deployment for a small team, but it is worth breaking down the infrastructure requirements more precisely so you can plan for your specific situation.
Mattermost's Team Edition is the free, self-hosted open source version. It runs well on a single server with 4 GB of RAM for teams up to roughly 1,000 users. A Hetzner CX22 at $6 per month handles the Node.js/Go binary and its PostgreSQL database comfortably for teams under 200. The full-text search feature — which indexes all message history — benefits from more RAM and a fast SSD, as the PostgreSQL index grows with message volume over time. For a team that has been on Mattermost for two years and sending thousands of messages per day, budget for 50-100 GB of disk at minimum and consider the database instance requirements separately if you are running PostgreSQL on the same host.
Unlike Slack, where file storage is billed per user and upgrades are required to expand it, Mattermost file storage is limited only by your disk. Files uploaded to Mattermost can be stored locally or offloaded to any S3-compatible object store — Backblaze B2 at $0.006 per GB per month makes unlimited team file storage cost essentially nothing at typical usage volumes.
Audio and video calling is the most commonly cited limitation of Mattermost's free tier. Slack bundles Huddles with its paid plans. Mattermost relies on plugins: the Jitsi Meet plugin is free and open source, allowing you to run video calls entirely within your own infrastructure if you self-host a Jitsi instance alongside Mattermost. Running Jitsi adds roughly $10-15 per month in VPS costs depending on concurrent call volume. A turn/stun server is required for reliable connectivity through corporate firewalls — Coturn is the standard open source choice and runs on the same VPS. The total stack — Mattermost + Jitsi + Coturn — costs around $20-25 per month for a 50-person team, compared to $5,250 per year for Slack Pro. The ROI calculation is not close.
For the integration ecosystem gap, Mattermost has roughly 100+ plugins covering the most common development tools: GitHub, GitLab, Jira, Pagerduty, Grafana, Prometheus, Zoom, and others. The Mattermost Marketplace is not as large as Slack's App Directory, but it covers the workflows that engineering and operations teams actually use. If your team relies on unusual Slack integrations, verifying plugin availability before migrating is worthwhile.
Security, Compliance, and Data Residency Advantages
This is where Mattermost self-hosted wins unconditionally. Slack's compliance-friendly features — message export, HIPAA BAA, data residency, eDiscovery — are locked behind Enterprise Grid, which runs $25-35 per user per month and requires a direct sales process with a contract. A 50-person team needing compliance export pays $15,000 to $21,000 per year just for the privilege of owning their own message data.
Mattermost Team Edition includes compliance export as a standard feature. You own the data, it lives in your PostgreSQL database, and you can query or export it at any time without additional payment. HIPAA-covered organizations can run Mattermost on infrastructure they control, sign their own BAA with their cloud provider, and have a compliant messaging solution for the cost of the server.
Data residency is equally straightforward: your data lives wherever your server lives. European companies concerned about Schrems II and GDPR compliance can run Mattermost on servers in EU data centers — Hetzner in Falkenstein or Nuremberg, OVH in Strasbourg, or any other EU-based provider — with zero data ever touching US-hosted infrastructure. This is a meaningful compliance posture that is simply unavailable on Slack without the most expensive Enterprise tier.
Organizations in defense, government, and financial services often have requirements for air-gapped or on-premises deployments. Mattermost's architecture supports fully disconnected environments without any callbacks to external services, which is a capability no SaaS communication tool can match by definition.
The security audit picture is also favorable. Mattermost's source code is auditable, and multiple independent security firms have published audits of the codebase. The open source model means vulnerabilities discovered by security researchers are disclosed publicly and patched quickly — the same transparency that makes Linux trustworthy in critical infrastructure.
Migration Path and Team Transition Strategy
Migrating from Slack to Mattermost is a workflow and cultural change as much as a technical one. Most teams find the technical migration straightforward and the people transition more challenging.
On the technical side, Mattermost ships a Slack import tool that handles message history, channels, direct messages, and user accounts from a Slack export. Slack's free plan limits exports to 90 days of history, while paid plans allow full history export through the compliance export feature. If you are on Slack Pro, export your full history before beginning the migration — once you cancel, that export window closes.
The channel structure in Mattermost maps directly to Slack's model: workspaces become teams, channels remain channels, and the DM/thread paradigm is familiar to anyone who has used Slack for more than a week. Thread behavior differs slightly — Mattermost threads have an optional setting to control whether replies appear in the main channel or only in the thread — which can be tuned to match your team's preference.
The migration timeline that works well in practice is a parallel-running period of one to two weeks. Keep Slack active and announce that the team will be using Mattermost for all new conversations starting on a specific date. This gives laggards time to get comfortable with the Mattermost apps (desktop and mobile apps are available for all platforms) before Slack becomes unavailable. The how-to-migrate-from-slack-to-mattermost guide covers the step-by-step process in detail.
One tactical consideration: if your team uses Slack Connect for communication with external partners and customers, Mattermost does not have an equivalent cross-organization channel feature. External partners would need accounts on your Mattermost instance or you would need to manage external communication via email. For teams with heavy Slack Connect usage, this is the most significant functional gap to plan around. For teams that primarily use Slack internally, the transition is seamless. See the Mattermost vs Rocket.Chat comparison if you want to evaluate a second open source option with slightly different feature tradeoffs before committing to either.
Total Cost of Ownership Over Three Years
The upfront analysis often focuses on monthly costs, but the three-year total cost of ownership tells a more complete story. Consider a 50-person team deciding between Slack Business+ and Mattermost self-hosted in 2026.
On Slack Business+, the math is straightforward: $15 per user per month times 50 users is $750 per month, or $9,000 per year. Over three years, that is $27,000 assuming no price increases — which is a generous assumption given Salesforce (Slack's parent) has a history of annual price adjustments. Add the cost of the engineering time spent managing Slack bot configurations, the admin overhead of adding and removing seats as the team changes, and the occasional incidents where Slack's own infrastructure causes outages beyond your control.
For Mattermost, the three-year calculation includes initial setup time (estimate 4 hours at your fully-loaded engineer cost), monthly maintenance time (roughly 30 minutes per month for updates and monitoring, or 18 hours total over three years), and infrastructure costs (a $14/month Hetzner server plus $2/month for backups and storage, totaling $576 over three years). If your average engineering rate is $100 per hour, the total cost of ownership for Mattermost over three years is roughly $576 + $2,200 in labor = approximately $2,776. Compare that to $27,000+ for Slack and the savings are $24,000 over three years — enough to fund a significant feature development sprint or hire a part-time contractor.
The labor cost estimate is honest and worth scrutinizing. If your team has no DevOps capability and would need to hire externally to set up and maintain Mattermost, the calculus changes. But for any team with a developer or DevOps engineer comfortable with Docker and Linux, the maintenance burden is genuinely light. Monthly updates are a single Docker pull and restart command. The how-to-calculate ROI on switching to open source guide provides a more detailed framework for this calculation across multiple tools simultaneously.
See the full Slack vs Mattermost comparison on OSSAlt — features, integrations, and deployment options side by side.
See open source alternatives to Slack on OSSAlt.