M&A Case for a Customer-First Playbook

When First Union Bank acquired CoreStates Financial in 1997, it didn’t count on the effect the merger would have on customers. Integration blunders forced moves to automated and online channels, clerical errors, and stepped-up competition led to First Union losing 20% of its inherited customers.

When banks merge, some customers leave, taking deposits and bank revenue with them. It’s a bigger problem than many bankers realize. In fact, customers in general are three times more likely to switch after a merger. 

So, when we talk about post-merger customer retention, we are really talking about preserving revenue, deposit stability and franchise value. Those are all factors that can affect the success of a merger.

When the ABA Banking Journal looked at the 10 biggest bank mergers of 2025, they found an average deposit loss of 3%. But others have reported loss of 5% or more, particularly if branches close. 

For example, when two Massachusetts banks, Independent Bank Corp. and Enterprise Bancorp, announced their merger in 2025, they estimated deposit runoff of 5%, which amounted to about $1 billion.

In terms of customer attrition, the rate runs as high as 20-30% post-merger. 

The worst case is when best customers leave. The traditional 80-20 rule says that 80% of bank revenue and profit comes from 20% of its customers. When best customers leave, their revenue is more difficult to replace.

When financial institutions merge, the focus understandably is on getting the integration right. That means extra attention on operations, efficiency, account transition, compliance, and all the other details that need to work correctly after the combination. Customer retention, while obviously important, may not be treated with the same urgency.

As a result, customers may feel left out. Their branch may be gone. Their relationship manager may not remain. They may find there are new methods and systems to learn. Fees may change, often for the worse. For some, it is a mild irritation. But others may figure: if it’s not the bank I knew, why stick around?

Retaining customers through a merger requires more than operational efficiency — it demands a deliberate, people-centered strategy from day one.

Assign dedicated teams — or at minimum, designated roles — whose primary job is to monitor transition friction and help customers navigate change. These teams should have clear escalation paths, access to account data to flag early warning signs of attrition (like reduced transaction activity or closed accounts), and the authority to resolve issues quickly. Having a human point of contact during a merger can be the difference between a customer staying or walking away.

What gets measured gets managed. Establish baseline attrition benchmarks before the merger closes, then set realistic but ambitious targets for the post-merger integration period. Break those metrics down by customer segment: small business owners, long-tenured depositors, and loan customers each carry different risk profiles and departure triggers. Review attrition data at regular intervals and be willing to adjust your strategy in real time if numbers trend in the wrong direction.

Develop a communication calendar that gets ahead of major milestones — system conversions, branch changes, new product terms — rather than reacting after the fact. Important messages should be reinforced through multiple touchpoints over time rather than relying on a single announcement, including direct mail, email and push notifications for digital users, and in-branch signage and staff conversations for walk-in traffic. Communication should be coordinated across marketing, frontline staff, relationship managers, and customer service teams so customers receive consistent information regardless of how they interact with the institution Plain language matters here; avoid jargon about "platform consolidation" or "product rationalization" and instead explain what's actually changing for the customer and when.  

Give customers a clear, easy way to ask questions and raise concerns — a dedicated merger hotline, a staffed inbox, or an FAQ portal with regular updates. Make these channels visible and promote them proactively. The goal isn't just to field complaints; it's to signal that the bank values the relationship enough to listen.

But listening without responding erodes trust faster than not asking at all. Build a process for reviewing incoming feedback, identifying common themes, and acting on them — then communicate those actions back to customers. Even a simple acknowledgment reinforces that the bank takes the relationship seriously. For CFIs, that responsiveness is often the core differentiator from larger competitors, and a merger is an opportunity to demonstrate it under pressure.

OceanFirst Bank of New Jersey boasts that it retains 96-97% of customers after a merger. OceanFirst is in the midst of merging with Flushing Financial, its eighth acquisition, and expects to maintain the same level of customer retention by sticking to their successful merger playbook.

First, OceanFirst communicates with the acquired bank employees, assuring those who are customer-facing that they will retain their jobs and may have additional career opportunities. Role consolidation does happen, but it's focused on back-office, administrative, and operational functions — not the frontline staff that customers interact with daily.

Then they launch a strategic marketing campaign to introduce OceanFirst to its new customers by investing in the local community. The OceanFirst Foundation supports local nonprofits to show OceanFirst planting roots in the community - not extracting them. 

The bank also works to reduce friction during a merger by seeking to smooth out operational changes that may affect customers by keeping as many local branches as possible. In the Flushing Financial acquisition, OceanFirst is committed to keeping all 30 branches open, describing Flushing's footprint as efficient and well-situated.

OceanFirst CEO Chris Maher told Banking Dive, “From a customer perspective, if the branches remain the same, staff remains the same, and you do a careful and low-impact integration, you’re going to have a very successful outcome.”

OceanFirst's approach highlights an often-overlooked reality of bank mergers: customer retention requires as much planning and attention as operational integration. CFIs that treat customer retention as a strategic priority from the moment a deal is announced, rather than an afterthought once integration chaos settles, are the ones that can better protect franchise value and emerge stronger. In a consolidating industry, how a CFI handles its next merger may matter as much as why it did the deal in the first place.