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Slack vs Microsoft Teams (2026): Which Wins Your Use Case?
By the TCCT editorial team · Last tested March 2026
Before you compare tools — which consolidation wave is your company in?
Wave A — M365 mandate
Your CFO already pays for Teams via E3/E5. Slack's days are numbered.
Start here →Wave B — PM tool eating docs
Your PM tool will own docs + chat in 18 months. Pick the one with the best doc layer.
Explore →Wave C — AI meeting tools
Granola/Fathom owns meeting notes by 2027. Pick a PM tool with a clean API.
Learn more →Microsoft Teams
8.4/10- Floor:
- £0 (M365 bundled)
- Best for:
- M365-mandated organisations
Before you compare: which wave are you in?
This comparison only matters if you have a genuine choice. For most companies, the decision is already made:
- If your CFO already pays for M365 E3/E5: Teams is the answer. The incremental cost of Slack (£312.50/month for 25 seats on Business+) is overlap that delivers no value past month 3 for most workflows.
- If you’re not in an M365 shop: read this comparison — you have a real choice.
Head-to-head on what matters
| Feature | Slack | Microsoft Teams |
|---|---|---|
| Incremental cost in M365 E3 shop | GBP 12.50/user/month | GBP 0 |
| App ecosystem | 2,400+ apps | 1,000+ apps (more variable quality) |
| Threading model | Clean | Confusing — in-channel or in-thread simultaneously |
| Search quality | Excellent | Moderate — tested on 3-month history recall |
| SSO/SAML | Business+ (GBP 12.50) | Included in E3 |
| Meeting infrastructure | Huddle (basic) | Full meeting suite — Copilot transcription on E3+ |
| Compliance (eDiscovery, legal hold) | Enterprise Grid only | Native via Purview |
| GitHub integration quality | First-party, excellent | Third-party, more friction |
| SharePoint/OneDrive native | Integration only | Native |
| UX / onboarding friction | Lower | Higher |
The cost maths for a 25-seat M365 shop
Running Slack (Business+) AND Teams (E3) in parallel:
- Slack cost: £312.50/month
- Teams incremental: £0
- Monthly overlap: £312.50
- Annual overlap: £3,750
For most workflows past month 3, the parallel-run delivers no incremental value. The honest advice: run a 6-week pilot of Teams-only, accept 90 days of engineering friction, and reclaim the £312.50/month.
Verdict by segment
Choose Slack if you are:
- A BYO-stack company with 5+ SaaS tools and no M365 mandate
- An engineering-heavy team where talent retention includes tooling preferences
- A startup under 50 people with no compliance mandate
Choose Teams if you are:
- Any company already on M365 E3/E5
- A compliance-heavy organisation needing Purview/eDiscovery
- A meeting-heavy organisation that values Copilot transcription and Outlook scheduling
The engineering revolt problem
Every Teams migration we’ve studied has an engineering revolt phase. Engineering teams cite: worse threading (confusing), slower search, inferior GitHub integration, and general UX friction. This is real and lasts 60-90 days.
The companies that handle it well: give engineering a migration timeline, a named integration owner, and an honest acknowledgement that Teams’ GitHub integration is worse. Don’t pretend otherwise.
The companies that handle it badly: announce Teams, turn off Slack, leave engineering to figure it out. 6-month stabilisation time, ongoing resentment.
FAQs
Can I run Slack and Teams permanently in parallel?
Technically yes. Strategically: it’s expensive (£312.50+/month of overlap for 25 seats) and creates communication fragmentation. Most organisations that try this end up picking one within 18 months.
Does Teams work without M365?
Teams is available standalone at £3.60/user/month. At this price, the app ecosystem gap vs Slack makes it harder to justify unless you have specific meeting/compliance requirements. Slack Pro (£6.75/user/month) is the better BYO-stack pick.
What about Slack Connect for external communication?
Slack Connect (external channels with clients or vendors who are also on Slack) is a genuine advantage. If your client list is heavily Slack-native, this is worth factoring into the cost comparison.