The real cost of a Microsoft 365 migration (and how to avoid overspending)

Microsoft 365 migrations have become almost routine in 2026 — but the cost varies wildly depending on how they're done. We've seen a 25-person firm charged £18,000 for a migration that should have cost £4,000. And we've seen another quote £2,500 that turned out to have missed half the steps needed. Here's an honest breakdown of what a proper migration costs, what drives that cost, and where businesses get burned.

What "a migration" actually involves

First, let's clarify what we mean by "Microsoft 365 migration". If you're moving from on-premise Exchange, Google Workspace, or another cloud email platform to Microsoft 365, a proper migration isn't just creating accounts and copying files. It typically involves:

• Discovery — auditing your current setup: mailboxes, user counts, shared mailboxes, distribution lists, calendars, contacts, shared drives.
• Tenant setup — configuring your Microsoft 365 tenant (or verifying an existing one), adding your domain, configuring DNS.
• User and mailbox provisioning — creating users, assigning licenses, setting up aliases.
• Email migration — moving historical email and folders from your old platform, usually in batches, with continuous sync at cutover.
• Calendar, contacts, and shared mailbox migration — often missed by cheap providers.
• SharePoint and OneDrive setup — where relevant, migrating file shares and setting up cloud storage.
• Teams rollout — setting up Teams, configuring policies, and training users.
• Security configuration — MFA, conditional access, email filtering, DLP, compliance policies.
• User training and post-migration support — usually forgotten entirely, leading to weeks of user confusion and productivity loss.

A realistic, professionally delivered migration of a 25-person firm takes 4–6 weeks of planning and 2–3 days of active migration, with several days of post-migration support.

The cost breakdown — an honest model

Here's what a well-run migration costs for a typical 25-user SME, assuming you're moving from on-premise Exchange:

Notice the range. A migration that skips user training, security config, or shared mailboxes lands at the bottom. A proper, well-delivered migration with post-migration support is at the top. Both are "migrations" — but they have very different outcomes.

What's not included in that price

Just so there are no surprises:

• Microsoft 365 licensing — that's paid directly to Microsoft (or your license reseller). Typical licensing for a 25-person SME ranges from £5–£30/user/month depending on the tier.
• Hardware refresh — if your current PCs are old and can't run modern Office, they may need replacing.
• Third-party tools — backup, MFA, or additional security tools may have separate costs.
• Ongoing managed IT — post-migration, most businesses move to a managed IT plan. Migration is a one-off project; ongoing management is separate.

If a quote looks significantly cheaper than this range, one of two things is happening: either they're skipping steps that will cause problems later, or they're subsidising the migration by locking you into an expensive ongoing contract. Ask both questions before you sign.

Where businesses get burned

1. Skipping the security configuration

This is the single biggest mistake we see. Moving to Microsoft 365 without proper MFA, conditional access, and email filtering leaves you exposed to the exact threats (BEC, phishing) that Microsoft 365 protects against — but only if configured properly. A "cheap" migration that skips this isn't cheap — it's a down-payment on a future incident.

2. Underestimating the "long tail" of migration

Email addresses, distribution lists, calendar permissions, shared mailboxes, public folders, signatures, aliases, forwarding rules — these take significant time to map and migrate correctly. Providers who quote based on "headline mailbox count" often cut corners here. The result: months of "why didn't this email arrive?" and "who has the shared mailbox?" confusion.

3. No user training

Microsoft 365 is not the same as on-premise Exchange. The interface is different, the features are different, and users need training. Businesses that skip training often report 3–6 months of "we moved to the cloud and everything is harder" — when the reality is that the migration was fine, but the users weren't supported.

4. Hidden licensing costs

If your old setup used cheap or "unofficial" licensing, migrating to Microsoft 365 means paying proper licensing costs. Some providers quote a migration price that looks low because they haven't accounted for the ongoing licensing delta. Make sure your quote covers the full licensing picture — not just the migration itself.

5. No backup solution

Microsoft does not provide backups of your data in the traditional sense. It provides high availability and geo-redundancy, but if a user deletes a folder, or a ransomware attack encrypts files, Microsoft can't restore them. A third-party backup solution is essential — typically £2–£5/user/month, and absolutely worth it.

How to keep costs under control

1. Get multiple quotes — and make sure they cover the same scope. Apples-to-apples comparison is essential.
2. Ask what's NOT included — training, security, backup, post-migration support. Every gap is a future cost.
3. Insist on a written migration plan — before work starts. It should cover discovery, migration, training, and post-migration support.
4. Plan for post-migration support — at least 2–4 weeks. Users will have questions.
5. Consider managed IT from day one — the migration is a good time to move to a proper ongoing support model. Bundling it often reduces overall cost.
6. Don't migrate on the cheap for "critical" workloads — email, shared files, and identity are the things that cost you most when they go wrong.

What good looks like

A well-run migration for a 25-person firm should:

• Take 4–6 weeks from start to finish, with 2–3 days of active migration.
• Include a written plan and risk assessment before any work starts.
• Result in zero or near-zero downtime for users.
• Cover email, calendars, contacts, shared mailboxes, and file storage.
• Configure MFA, conditional access, email filtering, and backup.
• Include hands-on user training (not just a PDF).
• Provide 2–4 weeks of post-migration support included in the price.
• Document everything, and hand over full admin access on completion.

If a provider can't tick all of those, the "cheap" migration will end up costing more — either in additional work later, or in the cost of the incident that results from skipped security steps.