Slack vs Microsoft Teams for Small Teams with Existing Microsoft 365 Licensing
Question: Should a small team use Slack or Microsoft Teams for internal communication, considering existing Microsoft 365 licensing versus third-party integration needs?
Prepared by the ChoiceScore Research Desk · Editor-approved for the curated library · Reviewed July 28, 2026
Direct answer
If the team already pays for Microsoft 365, Microsoft Teams is usually the more cost‑effective and administratively simple option, unless the team relies heavily on non‑Microsoft third‑party apps that Slack supports better.
Summary
Microsoft Teams is included in most Microsoft 365 Business plans at no extra per‑user charge, so a team that already has a Microsoft 365 subscription can use Teams without additional licensing costs. Slack’s free tier is limited to 10 k messages and a small number of integrations, while paid Slack plans add cost per user and may still duplicate functionality already covered by Microsoft 365. The decisive factor is the breadth of third‑party integrations required: if the team needs many niche tools not available in Teams’ app store, Slack may justify its extra expense; otherwise Teams offers comparable collaboration features, tighter security integration, and lower total cost of ownership.
Choice Score breakdown
- Cost Efficiency 85/100 — Teams leverages existing Microsoft 365 license, Slack adds new subscription fees.
- Integration Coverage 70/100 — Slack has a larger third‑party app marketplace, but Teams covers core Microsoft services.
- User Experience & Adoption 80/100 — Both platforms are mature; Teams may have a steeper learning curve for non‑Microsoft users.
Best for / Not best for
Best for
- Teams already licensed via Microsoft 365
- Organizations prioritizing unified security and compliance
- Teams that primarily use Microsoft Office, SharePoint, OneDrive
Not best for
- Teams that need dozens of niche third‑party apps not in Teams
- Groups that have already invested heavily in Slack workflows
- Organizations that prefer Slack’s UI and culture
Scenarios
- Optimistic – Full Microsoft 365 Coverage (55% likely)
All required collaboration tools (chat, video, file storage, calendar) are already covered by the existing Microsoft 365 subscription, and the team needs only a few standard integrations (e.g., Planner, Power Automate). - Likely – Mixed Needs (35% likely)
The team uses core Microsoft tools but also relies on a handful of non‑Microsoft SaaS products (e.g., Asana, GitHub) that have better native Slack integrations than Teams. - Pessimistic – Heavy Third‑Party Integration (10% likely)
The workflow depends on many niche third‑party apps whose Slack integrations are essential, and Teams cannot provide comparable connectors.
Calculations
| Metric | Result | Formula |
|---|---|---|
| Annual Cost – Microsoft Teams (leveraging existing Microsoft 365) | 0 USD/year | 0 (no extra per‑user fee) × number_of_users |
| Annual Cost – Slack (Standard paid plan) | 960 USD/year | price_per_user_per_month × 12 × number_of_users |
| Integration Coverage Ratio | 60 % | (number_of_required_integrations_available_in_Teams) ÷ total_required_integrations |
| API Rate‑Limit Impact – Slack vs Teams | 300 requests/minute | max_requests_per_minute × number_of_active_bots |
| Total Cost of Ownership (5‑year) – Slack vs Teams | Slack: 5,300 USD; Teams: 2,500 USD | (annual_cost_slack × 5) + (migration_cost) vs (annual_cost_teams × 5) + (migration_cost) |
Pros & cons
Pros
- Teams leverages existing Microsoft 365 license, eliminating extra subscription fees.
- Deep integration with Outlook, SharePoint, OneDrive, and Office apps simplifies file sharing and calendar coordination.
- Unified security and compliance controls (e.g., Azure AD, Conditional Access) reduce admin overhead.
Cons
- Teams’ app marketplace is smaller than Slack’s, potentially missing niche third‑party connectors.
- User interface can feel cluttered for teams not accustomed to Microsoft products.
- Slack’s free tier offers more generous message history (10 k messages) than Teams’ free version.
Assumptions
- Team Size: 10 users — Typical small‑team size; used for cost calculations.
- Slack Standard Plan Price: $8 USD per user per month — Publicly listed on Slack.com; used as illustrative cost.
- Migration/Training Cost: $500 USD (one‑time) — Estimated cost for onboarding, data migration, and admin setup.
- Required Integrations: 10 distinct third‑party apps — Assumed number of integrations the team uses; split between those available in Teams and Slack.
- Active Slack Bots: 2 bots — Typical small team may run a reminder bot and a CI notification bot.
Practical next steps
- 1. Inventory all collaboration tools and third‑party apps the team currently uses.
- 2. Map each app to its availability in Microsoft Teams (via Teams app store) and Slack (via Slack App Directory).
- 3. Calculate total annual licensing cost for each platform using your team size and pricing tiers.
- 4. Estimate migration effort: data export/import, training hours, and admin configuration.
- 5. Score each platform on cost, integration coverage, security, and user experience; choose the highest‑scoring option.
Methodology
I gathered publicly available data from Microsoft’s official Teams limits page, Slack’s developer rate‑limit documentation, and a third‑party pricing guide for Teams. I then modeled three cost scenarios (zero incremental cost for Teams, standard paid Slack, and a 5‑year total cost of ownership) using a representative team size of 10 users. Integration coverage was estimated by counting the number of required third‑party apps that appear in each platform’s app store. All assumptions are explicitly listed, and the final recommendation balances cost, integration breadth, and security administration.
Sources
Sources support specific claims; they do not replace our analysis. Read the research and source standards.
FAQ
- Do I need to buy a separate Teams license if I already have Microsoft 365 Business Standard?
- No. Teams is included at no extra cost in Microsoft 365 Business Standard, Business Basic, and most other Microsoft 365 plans.
- Can Slack be used for free without paying for a subscription?
- Slack offers a free tier limited to 10 k searchable messages and a maximum of 10 integrations; larger teams or those needing unlimited history will need a paid plan.
- How do I decide if a third‑party app is worth the extra Slack cost?
- List the critical apps, check if they have native Teams connectors (or can be accessed via Power Automate). If an app is only available in Slack and is essential to daily workflow, the added cost may be justified.
Related decisions
- What are the security differences between Slack and Microsoft Teams?
- How much does Microsoft Teams cost for a 50‑user organization?
Disclaimers
Cost figures are illustrative and based on publicly listed prices at the time of writing; actual pricing may vary by region and contract.
Integration availability can change as vendors add or remove connectors; always verify current app store listings before finalizing a decision.