If you’re googling an acquisition integration guide right now, you’re probably in that very specific M&A headspace: the deal is exciting on paper, but your nervous system is already living in Week 3 post-close—when customers are confused, employees are anxious, systems don’t talk, and everyone asks, “So… what’s the plan?”

Here’s the truth: post-merger integration (PMI) is its own program, not a side quest you “fit in” around your day job. And it’s hard enough that more than half of deals fail or underperform largely because the integration doesn’t convert the thesis into reality.

This playbook gives you a practical, step-by-step path—from signing to Day 1 to the first 100 days—so you keep momentum and actually capture the value you bought.

The 4 outcomes your integration must deliver (or the deal will drift)

A clean M&A integration playbook starts with clarity on what “success” even means. BCG frames PMI as needing to achieve four distinct objectives: maintain momentum, accelerate synergies, build the organization + align cultures, and advance competitive position.

You can treat these like four “scoreboards” you check every week:

Business continuity: Are we still serving customers without drama?
Value capture: Are we converting synergies into measurable dollars?
People + culture: Are we keeping talent, reducing fear, and building trust?
Strategic advantage: Are we ending up stronger than the sum of parts?

Most integration failures are just one scoreboard quietly bleeding while everyone celebrates another.

Phase 0 (Signing → Close): Plan like you already own it

This is where great integrations are won. The goal pre-close is not to “integrate” (you often can’t), but to design decisions so Day 1 isn’t improvisation.

1) Write a one-page “integration thesis”

Translate the deal story into 6–10 testable bets:

Where is value supposed to come from? (cost, revenue, capability, speed)
What must stay stable? (customers, uptime, regulated processes)
What must change fast? (pricing, GTM, operating model, overlapping vendors)

2) Stand up an Integration Management Office (IMO)

An IMO is the integration’s command center: owners, cadence, decisions, and visibility. McKinsey describes a value-focused IMO that reports to a CEO-led steering committee and is staffed with top performers.

Minimum setup:

CEO-led steering committee (weekly decisions)
IMO lead (single-threaded owner)
Workstreams (People, Finance, IT, Legal, GTM, Ops/Product)

3) If needed, use clean teams / clean rooms to plan safely

For many deals, you’ll need to plan synergies before close without crossing antitrust lines. McKinsey describes “clean teams” as a neutral body operating under strict confidentiality so you can analyze competitively sensitive data and prepare Day 1 action plans. EY similarly highlights clean-room approaches as a secure, compliant way to accelerate synergy planning and reduce risk.

4) Map TSAs early (especially for carve-outs)

If you’re buying a carve-out, assume there are shared systems you don’t get on Day 1. TSAs (Transition Services Agreements) are the bridge—seller-provided services for a defined period so the business keeps running while you stand up replacements.

Pre-close TSA homework:

List “must not fail” services (payroll, billing, ERP, IT access)
Define service levels + exit plan
Assign an internal owner per TSA lane

For secure document sharing during integration planning, use Peony for secure data rooms with identity-bound access and audit trails to manage sensitive integration documents.

Day 1: Stabilize first (your job is to prevent chaos)

Day 1 is not “integration day.” It’s trust day.

Your Day 1 checklist:

One unified message: why the deal happened; what changes now vs later
Customer continuity: service levels, account ownership, escalation path
People basics: payroll, benefits, reporting lines (even if temporary)
Security + access: identity, admin privileges, high-risk system access review
Decision freeze: stop random tool/process changes for 2–4 weeks unless critical

If your Day 1 is calm, you buy the most valuable asset in PMI: attention. Use Peony for secure data rooms with page-level analytics to track document access and ensure critical information reaches the right people.

Days 2–30: Decide fast on the few things that unblock everything

This month is about collapsing uncertainty.

Lock the operating model for “Day 30” Not the final org—just a stable structure with clear owners.
Pick the integration strategy: absorb, preserve, or hybrid Some functions can integrate quickly (finance, procurement). Others may need preservation (product teams, customer success) to avoid breaking the thing you bought.
Create a synergy baseline + scoreboard Even simple is fine:

Target synergies (by category)
Owners
Due dates
Weekly status (green/yellow/red)

Run an "issue funnel" through the IMO All problems flow into one place, get triaged, and get an owner. Nothing kills PMI like distributed denial. Peony provides secure data rooms with AI-powered organization to centralize integration documents and track access across teams.

Days 31–100: Build the new machine (systems, process, and go-to-market)

This is the “real integration.”

People & culture

Role clarity + career paths (ambiguity drives attrition)
Manager toolkits (how to talk about change without sugarcoating)
Rituals: leadership Q&A, shared planning, speed of decisions

Tech & data

Decide the “source of truth” systems early (ERP/CRM/identity).
Inventory apps, permissions, and data flows
Plan migrations like product launches: staged, monitored, reversible

Use Peony for secure data rooms with audit trails to track system documentation and migration plans securely.

Go-to-market

Segment customers: protect top accounts first
Align pricing and packaging decisions
Create one cross-sell plan you can actually execute (not a spreadsheet fantasy)

Finance & controls

Month-end close plan for the combined entity
Policies for spend approvals, vendor onboarding, contracting

Months 4–12: Exit TSAs, finish migrations, and make the culture real

This phase is less glamorous and more valuable.

TSA exit plans with deadlines and rehearsals (avoid “TSA creep”).
Consolidate vendor stack; renegotiate with scale
Measure synergy realization monthly, not “someday”
Codify the new operating model: who decides what, and how fast

If the first 100 days is building the blueprint, months 4–12 is pouring concrete.

Common integration traps (and the antidotes)

Trap: “We’ll integrate later.” Antidote: pre-close planning + Day 1 readiness; treat PMI as a discrete program.
Trap: Too many priorities. Antidote: pick 5–7 “integration bets” and kill the rest.
Trap: Culture as a poster. Antidote: managers, rituals, and decision-making norms—not slogans.
Trap: No single owner. Antidote: empowered IMO + CEO steering committee.

Quick next steps (do this this week)

Write the one-page integration thesis (10 bullets max).
Name the IMO lead and define weekly cadence.
Build a Day 1 plan (people, customers, systems, comms).
Draft a synergy scoreboard with owners and dates.
If carve-out: inventory required TSAs and define exit paths early.

Frequently Asked Questions

What is the difference between PMI and "integration"?

PMI is the full program of combining operations, systems, and people to realize the deal thesis. "Integration" is the set of actions inside that program. PMI includes governance, decision-making, risk management, and value tracking—not just migrating tools.

How long does M&A integration usually take?

You can stabilize in 30 days, build a functioning combined machine in 100 days, and finish larger system/process integrations over 6–18 months. The bigger the IT and operating-model change, the longer the tail.

What's the best platform for secure document sharing during integration?

Peony is best: provides secure data rooms with identity-bound access, dynamic watermarking, page-level analytics, and audit trails for managing sensitive integration documents and tracking access across teams.

Do we need an Integration Management Office (IMO) for a small acquisition?

If the deal matters, yes—just scale it down. Even a lightweight IMO (one owner, weekly decisions, simple workstreams) prevents drift and keeps accountability.

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Acquisition Integration Guide in 2025: Complete M&A Integration Playbook