Post Merger Integration Process

A five-phase methodology built for middle-market and PE-backed deals

Most published PMI methodologies are written by people who've never run one. They read as a sequence of abstract milestones — "align cultures," "realize synergies," "track performance" — without acknowledging the operational reality that determines whether any of it actually happens. Day 1 readiness gets compressed into a single weekend. Functional workstream leads get appointed two weeks after close. Synergy commitments made in diligence quietly disappear from the operating plan by Day 100.

The Stonehill process is built around how integrations actually run in middle-market and PE-backed deals. Five phases, each with defined timing, named deliverables, and the governance discipline to keep them on track. Senior practitioners stay on the work from pre-close through stabilization — no hand-off to a junior team, no escalation chain when a workstream stalls.

Phase 1 — Pre-Close: Integration Planning and Day 1 Readiness

Timing: Diligence through close

The decisions that determine whether an integration succeeds are made before close, not after. This phase aligns the integration plan to the investment thesis, builds the governance scaffolding, and ensures Day 1 is operationally ready — not just legally closed.

• Integration thesis validation against the synergy case in the diligence model

• EBITDA bridge construction with cost synergy, revenue synergy, and one-time cost line items

• Integration Management Office (IMO) design — leadership, cadence, reporting, escalation

• Sponsor coalition build with the executive layer that will carry adoption

• Functional workstream assignments and lead identification

• Day 1 readiness checklist across communications, customer stability, employee transitions, cash management, banking, IT access, and (where applicable) TSA dependencies

Phase 2 — Day 1 to Day 30: Stabilization

Timing: Close through Day 30

The first 30 days are about preserving value, not creating it. Customers stay, employees stay, cash flows, the lights stay on. Synergy capture starts in Phase 3 — not here.

• Communications cascade to employees, customers, vendors, lenders, and (where applicable) regulators

• Customer retention monitoring on the top 20% of accounts that drive 80% of revenue

• Cash management and banking continuity, especially in roll-up environments where treasury complexity compounds with each acquisition

• TSA management for carve-out transactions — exit sequencing, dependency mapping, cost tracking

• IMO governance launch — weekly cadence, workstream reporting, leadership review

• Quick-win identification — the visible early actions that signal momentum without overcommitting

Phase 3 — Day 30 to Day 100: Plan Execution

Timing: Day 30 through Day 100

The Day 100 plan is where most integrations either build credibility or lose it. This phase converts plans into deliverables, makes the hard operating model calls, and starts capturing the first synergy commitments.

• Functional workstream execution against the Day 100 deliverable plan — finance, HR, IT, operations, commercial, customer success

• Operating model design decisions — roles, spans, decision rights, process ownership

• Early synergy capture in procurement, vendor consolidation, redundant role elimination, and facility decisions

• Cultural integration through active leadership engagement, not surveys and posters

• Stakeholder communications cadence sustaining momentum past the initial close announcement

• Change management spine — ADKAR- and Kotter-grounded — built to carry adoption through Phase 4

Phase 4 — Day 100 to Year 1: Synergy Realization

Timing: Day 100 through close of Year 1

Synergy realization is where the deal proves its thesis. This phase converts identified synergies into captured ones, with the measurement architecture to prove it to the sponsor and to the next exit.

• Cost synergy capture and tracking against the diligence-stage bridge

• Revenue synergy enablement — cross-sell programs, channel consolidation, pricing actions

• Systems consolidation execution — ERP, CRM, HRIS, financial reporting, data architecture

• Performance management architecture — KPIs, dashboards, governance, and the reporting cadence that surfaces variance before it becomes a problem

• Talent and leadership decisions — the team that will run the post-integration business is rarely the team that closed it

• Operating model stabilization — process ownership, decision rights, and accountability institutionalized

Phase 5 — Year 1 Forward: Sustained Performance

Timing: Beyond Year 1

Integration ends when the new operating model is sustainable without integration scaffolding. This phase transitions ownership from the IMO to the line organization and institutionalizes the performance management discipline.

• IMO wind-down with capability transfer to functional leadership

• Performance management institutionalization — the cadence and rigor of integration carried forward as how the business is run

• Continuous improvement build-out for the next acquisition (in platform contexts where the next deal is already in diligence)

• Exit preparation and value creation story refinement, where the next transaction is on the horizon

If you have a transaction in diligence, just closed, or in stabilization and not tracking to the synergy case, we can help. Senior-led, scoped tight, embedded model.