Arthur J. Gallagher closed the $13.8 billion AssuredPartners acquisition on August 18, 2025, the largest deal in the company's history, and management has already raised the synergy target twice since, most recently to $325 million by early 2028. The company's back office integration, covering general ledger, HR, payroll, and treasury systems, is running ahead of plan and was live as of January 2026. But the number that actually carries the synergy math, the conversion of roughly 300 AssuredPartners branches onto Gallagher's agency management system, does not start in earnest until the second half of 2026 and will not finish until mid-2027. Everything Gallagher has claimed about integration success so far describes the easy part.

One thing worth flagging: Gallagher's own back office integration is reporting as ahead of plan, but the harder test, the conversion of roughly 300 AssuredPartners branches onto common agency management systems, has not started on the timeline that matters. Management is already citing synergy realization tied to a system that will not exist for another year.

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