The M&A Integration Checklist

Most M&A integrations fail in the first 90 days

The deal is signed. The champagne is poured. And then reality hits: two companies with different systems, different cultures, and different ways of working need to become one.

The first 90 days after close determine whether an acquisition creates value or destroys it. Get this window right, and you build momentum. Get it wrong, and you spend the next two years untangling the mess.

Why the first 90 days matter

Employees are watching. Customers are nervous. Suppliers are hedging. The longer uncertainty lasts, the more damage accumulates — in attrition, in lost deals, and in operational friction.

Speed doesn’t mean rushing. It means having a plan before close, executing it with precision, and communicating constantly.

Pre-close: Before day one

Appoint an integration lead with full authority. Map critical systems and identify overlaps. Document the top 10 integration risks and assign owners. Prepare day-one communications for all stakeholders. Secure access to both companies’ systems and data.

Days 1–30: Stabilise

Protect revenue. The single most important job in the first month is making sure customers don’t leave and orders keep flowing.

Announce the integration structure: who reports to whom, which systems stay, which go. Ambiguity breeds anxiety. Make decisions visible, even if some are provisional.

Run a full IT systems audit. Identify which systems serve the same function and document data flows between them. Don’t merge anything yet — just map the landscape.

Days 31–60: Align

Standardise processes where overlap exists: order-to-cash, procure-to-pay, and reporting. Pick the stronger process, not the acquiring company’s process by default.

Begin system consolidation planning. Decide on the target architecture: one ERP or two? Shared CRM or separate instances? Each decision should have a clear business case.

Start cultural integration. Joint team events, shared Slack channels, cross-company project teams. Culture integration doesn’t happen by memo — it happens through working together.

Days 61–90: Execute

Begin executing the system consolidation plan. Migrate users to unified platforms. Train teams on new processes and tools.

Measure integration progress against the targets set pre-close. Revenue retention, employee retention, system uptime, and process compliance are the four metrics that matter.

Document everything. The integration playbook you write now becomes the template for your next acquisition.

The integration roles you need

Integration Lead: one person, full authority, accountable for the 90-day plan. Workstream Owners: one per domain (IT, Finance, Operations, HR, Sales). Communication Lead: manages internal and external messaging. PMO: tracks milestones, risks, and dependencies.

What goes wrong most often

Decision paralysis. Too many stakeholders, not enough authority. Fix this by appointing a single integration lead before close.

IT underinvestment. Companies save on the deal by cutting the integration budget. You’ll pay three times more to fix it later.

Ignoring culture. You can merge systems in 90 days. Culture takes years. Start early and be deliberate about it.