If you are running a phased BitTitan migration, plan for the period where users in both the source and destination tenants need active licenses at the same time.

In a wave-based BitTitan migration program, users who have already cut over require active Exchange Online licensing in the destination tenant, while users who have not yet migrated still need active licenses in the source tenant. Throughout the wave period, both tenant license pools must remain available concurrently.

That dual-licensing window has direct cost impact, particularly in acquisition scenarios where the goal is to reduce overall license spend after consolidation. Source tenant licenses cannot be cancelled until all users have been migrated and the source tenant has been fully decommissioned. If source tenant licenses are removed before migration completes, BitTitan loses the source-side mailbox access required for migration jobs.

Estimate the overlap by using the full wave timeline from first cutover to last cutover. For example, in a three-wave program spanning 12 weeks, the dual-licensing period is approximately 12 weeks. That overlap cost should be included in the migration program budget up front, not discovered after approval.

Have you calculated the BitTitan migration dual-licensing overlap period and included that cost in your migration program budget?

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