Post merger integration: capturing cost synergies

Where post merger cost synergies actually sit

On UK mid-market deals, most cost synergies sit in four places: duplicated third-party spend, overlapping overhead, consolidated property and IT, and pricing leverage from a bigger combined book. The mix shifts by deal type, but the sequence for capturing them is broadly the same.

• Third-party spend: duplicated suppliers, split contracts, price harmonisation
• Overhead: back-office overlap, span-of-control, duplicated systems licences
• Property & IT: footprint consolidation, contract rationalisation
• Commercial: pricing consistency and combined volume leverage

Sizing cost synergies before day one

Deal-model synergy numbers are rarely wrong on total - they are usually wrong on phasing. A pre-close sizing exercise turns the model line into a category-level view: how much is duplicated spend, how much is renegotiation, and how much needs operational change before it lands.

• Combined spend cube across both entities - vendor, category, cost centre
• Duplicate supplier mapping and top-20 contract review
• Overhead overlap analysis by function
• Realistic phasing: day 100, month 6, month 12, run-rate

The 100-day post merger integration plan

Weeks 1-4: baseline and no-regret moves

• Combined spend baseline signed off by finance
• Freeze duplicate discretionary spend categories
• Pause any renewals landing in the first six months for review

Weeks 5-8: quick wins and mobilisation

• Renegotiate the top 5-10 duplicated supplier contracts
• Consolidate overlapping SaaS and telco
• Stand up a finance-owned synergy tracker

Weeks 9-13: lock in run-rate

• Finance-validated run-rate savings, tracked to the ledger
• Named owner and cadence for every remaining workstream
• Board readout: delivered, in-flight, year-two pipeline

What a realistic synergy prize looks like

For a UK mid-market combination with £50-200m of combined addressable spend, a well-run integration typically lands 4-8% of run-rate cost synergies by day 100, with a further 5-10% in the pipeline for months 4-12. Deals with heavy overlap in category, geography or overhead sit at the top of that range.

Common post merger integration mistakes

• Waiting for the target operating model before touching supplier spend
• Letting each entity keep its own procurement policy for "a transition period"
• Tracking synergies in a spreadsheet finance never signs
• Sequencing overhead cuts before the commercial change is landed

Questions PE and corporate buyers ask

How long does post merger integration take?

The formal integration is usually a 12-18 month programme, but the cost synergy window is much tighter - most of what will land in year one is committed in the first 100 days.

How much of the deal-model synergy actually lands?

Independent studies put full realisation on cost synergies at 60-80% for well-run integrations, and materially lower when the first 100 days drift. Phasing discipline matters more than the headline number in the model.

Who should own post merger cost synergies?

A single accountable owner reporting to the CFO or portfolio operating partner, supported by category leads. Diffused ownership across "each business" is the most common reason synergies slip.

Where this connects

Post merger integration draws on our cost reduction and interim procurement services, and pairs with the 100 day cost plan and the EBITDA improvement guide.