One to two weeks end to end. The part your staff actually notice is usually one evening.
Resources / How long does a Microsoft 365 migration actually take?
For a business of 5 to 25 people, plan on one to two weeks end to end, with the actual cutover in a single after-hours window. Most of that fortnight is discovery and background mailbox syncing that happens while everyone keeps working normally on the old system. Migrations start from $1,200. The part your staff experience is usually one evening and about fifteen minutes each the next morning.
End to end, for 5 to 25 people
The cutover window staff notice
A clean small business migration
Very little of it is the migration itself. The first two days are discovery: how many mailboxes there are and how large, what system they are on now, who controls the domain's DNS, which addresses are shared mailboxes rather than people, what distribution lists exist, what devices everyone uses, and who needs which licence. Skipping this is the single most common reason a migration goes badly.
The next few days are tenant setup and licensing: creating the Microsoft 365 tenant, verifying domain ownership, creating accounts and groups, and assigning licences. Nothing has moved yet and nothing is disrupted.
Then the mailboxes pre-sync. Their contents copy across in the background, over hours or days depending on size, while everyone carries on using the old system as normal. This is the bulk of the calendar time and almost none of the disruption.
The cutover evening is short by comparison: a final catch-up sync of anything that arrived since, the DNS change that redirects mail to the new mailboxes, and client reconfiguration. Then a few days of settling while stragglers get their phones sorted out.
Mail routing follows the MX record in your domain's DNS. Until that record changes, mail keeps being delivered to the old system, and Microsoft's own documentation is explicit that email continues to route to the old mailboxes until the MX record is changed.
That means the switch is a moment, not a gradual thing, and doing it at eleven on a Tuesday morning splits the day's mail across two systems while people are trying to work. Doing it in the evening or over a weekend means the final catch-up sync is small, DNS changes have overnight to propagate, and people arrive to one mailbox with everything in it.
There is no true zero downtime option for a small business migration, and anyone promising one is describing a much larger and more expensive piece of work. What there is instead is a well chosen window where the disruption lands outside working hours.
Mailbox count and size matter most. Microsoft's cutover method, used when you are coming from an on-premises Exchange server, supports up to 2,000 mailboxes, but Microsoft recommends migrating 150 or fewer because of how long larger batches take. A small business is nowhere near either number, which is why these migrations are measured in days rather than months.
Where you are coming from changes the method. Google Workspace, a generic IMAP host, an old on-premises Exchange server and a hosted cPanel mailbox all migrate differently, and some carry across calendars and contacts more cleanly than others. That gets decided in discovery, not on the night.
Then there is structure: how many shared mailboxes and distribution lists exist, whether anyone is using public folders, how much sits in archive files on individual laptops. And bandwidth, since everything has to upload.
The most common cause of delay is none of those. It is DNS access. If nobody in the business can log into the domain registrar, or the previous IT provider holds the domain and does not reply, the migration stops until that is resolved. It is an administrative problem, not a technical one, and it is why we check it on day one.
Nobody knows who registered the domain. The previous IT person controls the DNS and has stopped answering. Mailboxes turn out to be four times larger than anyone estimated because nothing has ever been archived. Several shared addresses are actually personal accounts that six people log into with the same password. There are devices too old to handle modern authentication.
Every one of those is findable in a two day discovery and expensive to find on cutover night. That is the entire argument for the discovery step, and it is why we will not quote a migration without doing one.
Realistically: they sign out, sign in again with their email address and a new password, approve a multi-factor prompt on their phone, and Outlook rebuilds itself. Their old mail is already there because it was pre-synced over the previous week. Mobile devices need the account removed and re-added, which is the step most people need a hand with.
For most people that is fifteen minutes on the first morning. The ones who need longer are usually those with very large mailboxes, several shared accounts, or a phone nobody has updated in three years.
Sending a short note the day before with the new sign-in details and what to expect removes most of the friction. The technical work is rarely what makes a migration feel bad. A surprise is.
Yes. Mail, calendar and contacts move across for each mailbox. Nothing is deleted from the source system when the migration completes, which is the safety net: if something looks missing in the first fortnight, the original is still sitting there to check against.
One thing worth knowing once you are on Microsoft 365: the platform is not a backup. Deleted items sit in retention windows measured in weeks, not years, and Microsoft's own agreement puts the responsibility for backing up your content on you. That is a separate decision to make after the migration, not part of it.
A clean migration for a 5 to 25 person business starts from $1,200, covering discovery, tenant setup, the mailbox migration itself, the after-hours cutover and the first days of support afterwards. The exact number depends on mailbox count and sizes, the source system and how much shared structure needs rebuilding, which is what discovery establishes.
A discovery call is free and takes about half an hour. Tell us how many people you have and what you are on now, and you will get a fixed quote in writing within a business day, along with an honest view of whether the timing suits your business.
The 10-step Microsoft 365 migration plan: The full playbook we run, step by step, and what it costs.
Does Microsoft back up my emails and files?: Mostly no. What retention actually covers, and what it does not.
Managed IT support: One accountable partner after the migration, not just during it.
Services and pricing: The full price list, in plain English.
For 5 to 25 people, plan on one to two weeks end to end. Most of that is discovery and background mailbox syncing that happens while everyone keeps working. The cutover itself is a single after-hours window, usually an evening or a weekend.
There is a short window during the cutover, which is why it is scheduled outside working hours. Mail keeps routing to the old system until the MX record changes, so the switch is a moment rather than a gradual handover. Most staff notice about fifteen minutes of setup the following morning.
Yes, all three move for each mailbox. Nothing is deleted from the source system when the migration completes, so the original remains available to check against if anything looks missing in the first couple of weeks.
Most often it is DNS access rather than anything technical: nobody can log into the domain registrar, or a previous IT provider holds the domain and will not respond. Oversized mailboxes, shared addresses that are really personal accounts, and devices too old for modern authentication are the other common ones.
From $1,200 for a clean migration of a 5 to 25 person business, covering discovery, tenant setup, the mailbox move, the after-hours cutover and initial support. The final number depends on mailbox count and size, the system you are coming from, and how much shared structure needs rebuilding.
Tell us your team size and current setup. We will map what fits, honestly, with a fixed quote in one business day. Free 30-minute discovery call, no obligation.
Prefer to talk? Call (02) 9053 8789.
Belivanis Information Systems