Teams is often pitched as "free with Microsoft 365" — but the hidden costs of switching from Slack are real: months of disruption, lost message history, bot rebuilds, and a team that communicates less effectively while adapting.
Slack Pro costs $8.75/user/month (annual). A 50-person company pays ~$5,250/year. If they already pay for Microsoft 365 Business ($12.50+/user/month), Teams is available at no incremental cost — making the saving ~$5,250/year before migration costs.
But Slack has deep integrations (GitHub, Jira, PagerDuty, CI pipelines), curated channels, and years of searchable history. Teams offers better video conferencing and SharePoint integration. The switch is often driven by IT standardisation rather than pure cost — which affects how you should weigh the disruption cost.
Conservative estimates for a 30–50 person team on Slack Pro, already on M365. Adjust everything to your situation.
| Input | Suggested Value | Notes |
|---|---|---|
| Current monthly cost (Slack) | $350 | Pro plan, 40 users |
| New monthly cost (Teams) | $0 | Included in existing M365 licence |
| Contract months remaining | 4 | Slack annual contract mid-point |
| Migration hours | 60 | Channel setup + bot rebuilds + QA |
| Staff hourly rate | $80 | IT admin + developer time blend |
| Retraining hours / person | 3 | Teams orientation session |
| Staff needing training | 40 | All Slack users |
| Downtime hours (total) | 80 | Communication friction across team |
| Downtime cost / hour | $60 | Reduced velocity estimate |
| Risk buffer | 10% | Low technical risk, high adoption risk |
Pre-filled with the values above. Change any number to see your real payback timeline.
Open Calculator with These ValuesAll values are editable. Results are estimates — consult your IT and finance teams.
Slack message history does not natively import into Teams. Third-party tools (Cloudiway, Mover, AvePoint) can migrate message data, but the experience in Teams differs significantly. DMs don't map cleanly to Teams chats, and threaded replies often break. Most organisations treat history migration as a compliance archive rather than a live migration.
Teams covers the core messaging use cases. However, Slack has a richer app ecosystem (3,000+ integrations vs Teams' ~800), better search, and keyboard-first UX that power users rely on. Teams excels at video meetings, SharePoint/OneDrive integration, and org-wide broadcasting. For engineering-heavy teams, Slack's GitHub, Jira, and PagerDuty integrations are deeper.
A 2–4 week parallel run helps with adoption but doubles the confusion if communication splits across both tools. Set a hard cutover date, not an open-ended "we'll migrate gradually." Designate a Teams champion in each team to answer questions and prevent Slack regression. Without a clear cutoff, transitions drag on for months.