What Microsoft 365 Backup will actually cost you
Microsoft charges $0.15 per GB per month of protected content. The bill is driven by archives, recycle bins and file versions that don't appear in the usage reports most people check. Put your numbers in and see the whole thing.
Your tenant
Start with seats and average sizes. Rough numbers are fine — you can refine them later.
These three are estimates, not measurements
The parts nobody counts
Archives, recycle bins and versions are billable under native backup but are not reflected in the standard usage reports. They are usually why a quote comes in higher than expected.
Scoping and growth
Native pricing rewards protecting less. Most tenants should scope per site and mailbox rather than protect everything.
Why this number is usually wrong the first time
Microsoft publishes a pricing calculator, but it's a spreadsheet you download and fill in by hand after collecting sizes from PowerShell or the usage reports. Those reports leave out recycle bin contents and online archives, both of which are billable. If you size a backup budget from them alone, you will under-forecast.
The other thing the reports won't tell you: the bill follows your storage curve, not your headcount. A tenant with a decade of project archives sitting in SharePoint pays for all of it every month unless someone scopes the policy deliberately.
What we'd check next
We're building a version that connects to your tenant with read-only permissions and fills these fields in from real data — measured sizes, unprotected mailboxes, leaver accounts approaching deletion, and which sites are safe to leave out of scope.