Why M&A Due Diligence Takes So Long (And How to Fix It)

Quick answer

M&A due diligence takes so long because most teams still run the process across disconnected workstreams, document repositories, spreadsheets, and memo drafts. Boston Consulting Group reported that the average time from announcement to close for deals above $2 billion reached 191 days, with about 40% of transactions taking longer to close than announced at signing [Boston Consulting Group, "The 2024 M&A Report: Deals Are Taking Longer to Close. How to Respond.", 2024].

The slow part of diligence is usually not the analysis itself. It is the operating model around the analysis. Teams lose time collecting missing files, reconciling which version is current, translating findings across workstreams, and rebuilding the same story for deal leads, partners, lenders, and the investment committee.

That matters because timeline drag is no longer a small process problem. Boston Consulting Group reported that the average time from announcement to close for deals above $2 billion reached 191 days in 2024 and that about 40 percent of announced transactions took longer to close than expected [Boston Consulting Group, "The 2024 M&A Report: Deals Are Taking Longer to Close. How to Respond.", 2024]. Bayes Business School also reported that the average pre-announcement due diligence period reached 203 days across studied deals from 2013 to 2022 [Bayes Business School, "Cautious M&A investors taking extra care with due diligence", 2024]. That does not mean every extra day is a diligence failure, but it does show how expensive weak diligence execution becomes when the process starts to sprawl.

Why diligence feels slow even when teams are working hard

Most deals do not slow down because the team is idle. They slow down because the workflow repeatedly forces smart people to re-establish context.

A typical delay pattern looks like this:

1. 1. Management sends partial files.
2. 2. Specialists start reviewing what they have.
3. 3. New documents arrive that change the picture.
4. 4. Findings sit in separate tools by workstream.
5. 5. Leadership wants a current view across all issues.
6. 6. The team rebuilds the story one more time.

That cycle can happen multiple times before sign or close. The hours are real, but they do not all produce forward motion.

Cause 1: The file flow is still chaotic

Most diligence delays begin before any serious analysis starts. Files arrive late, are named inconsistently, or appear without enough context to know whether they are current, complete, or relevant.

• Financial schedules show up in multiple versions.
• Contracts are uploaded without clear priority.
• Tax files arrive without period coverage explanations.
• Management responses live in email instead of the review record.
• Analysts do not know which files are final and which are placeholders.

This creates a hidden tax on the process. Analysts are not spending those hours doing diligence. They are spending them finding the right starting point.

The practical consequence is not just delay in the first week. Poor file hygiene cascades into every later step because the team never fully trusts the base record.

Cause 2: Financial, tax, and legal teams run on different operating rhythms

Even strong diligence teams lose time when each workstream runs inside its own tools and cadence.

• Financial DD works from models and spreadsheets.
• Tax DD collects return packages and exposure notes.
• Legal DD lives inside document review trackers and counsel comments.
• Commercial or operational reviewers maintain separate interview notes and market views.

Each stream may be individually competent, but the process still slows when no shared record exists for how the issues connect.

Bain's 2025 M&A report argues that assured value capture begins with faster, deeper, and more focused diligence that takes later execution seriously during diligence rather than after it [Bain & Company, "Looking Ahead to 2025: Preparing for What Comes Next", 2025]. That is difficult when the workstreams cannot see each other clearly enough to escalate the same issue in a shared way.

Cause 3: The synthesis starts too late

Many teams underestimate how much time the last mile consumes. The analysis may already exist, but leadership still needs a decision-ready view that answers basic questions quickly:

• What changed since the last review?
• Which issues are truly material?
• What evidence supports each conclusion?
• Which questions are still open?
• What should happen to price, structure, or diligence scope because of those findings?

That synthesis often begins only after specialist work is mostly complete. By then, the team is trying to move findings from spreadsheets, PDFs, tracked comments, and side conversations into a narrative that can survive committee scrutiny under maximum time pressure.

This is one reason long diligence cycles still feel rushed. The process is long, but the synthesis window is still compressed.

Cause 4: Findings do not stay attached to source evidence

Delays also happen when the team cannot move quickly from a summarized issue back to the supporting source material.

McKinsey notes that M&A is resource-intensive and that GenAI can materially improve the process by expediting diligence and negotiation tasks [McKinsey & Company, "Gen AI: Opportunities in M&A", May 21, 2024]. But speed gains disappear when the team cannot validate what it is seeing.

In practice, that means momentum drops when:

• the issue summary is detached from the source file
• reviewers cannot see who changed the conclusion
• late questions require a manual scavenger hunt
• the current answer exists only in someone’s head or inbox

This is where many processes become deceptively slow. The team appears to have an answer, but the answer is not reviewable enough to move forward confidently.

Cause 5: Pre-LOI work gets discarded

Pre-LOI diligence often surfaces useful signals, but many teams treat that early effort as disposable. Then post-LOI diligence begins as if nothing meaningful has already been learned.

That restart creates duplicate work and forces the team to recover context it already had once:

• early financial concerns have to be rediscovered
• key contracts get re-prioritized manually
• tax or legal flags must be restated for new audiences
• management credibility concerns are remembered informally rather than preserved structurally

When early financial, tax, and legal concerns are preserved, the later process starts with sharper questions and better prioritization. When they are not, the team spends the first part of post-LOI diligence reconstructing the same insight base.

Cause 6: Every audience requires a different format

Diligence almost never has just one audience. The same underlying work has to serve:

• analysts and associates doing the review
• partners and deal leads deciding where to push deeper
• lenders assessing risk and structure
• legal teams shaping protections
• investment committee members who need the conclusion fast

If the operating model cannot support all of those audiences from one live record, the team starts reformatting rather than reviewing. That is one of the most common reasons a process feels busy while still moving slowly.

What actually compresses the timeline

The fix is not simply more people. In many deals, more people just create more translation overhead. The real fix is a better operating model.

This is the operating distinction between a diligence process that looks busy and one that actually moves.

What faster teams do differently

The fastest serious teams are not the ones that skip diligence. They are the ones that remove waste from how diligence is run.

They usually do five things well:

1. 1. They define the first request set deliberately. They do not ask for everything. They ask for what will sharpen the buyer's view fastest.
2. 2. They prioritize issues visibly. Not every finding deserves the same review clock.
3. 3. They keep one current answer per issue. No parallel truths across spreadsheets, memos, and chat threads.
4. 4. They build the executive narrative while the work is live. Not after the specialists are done.
5. 5. They carry early context forward. Pre-LOI work becomes the front end of full diligence rather than a disposable draft.

Those practices sound operational because they are. Timeline compression usually comes from operating discipline, not analytical shortcuts.

Where AI helps and where it does not

Deloitte reported that 86 percent of surveyed organizations have integrated GenAI into M&A workflows [Deloitte, "2025 GenAI in M&A Study", 2025]. That matters because the technology can make parts of diligence materially faster:

• ingestion of large document sets
• extraction of recurring data fields
• first-pass summarization and issue clustering
• comparison across versions and document sets
• draft synthesis of recurring themes

But AI does not fix:

• missing files
• poor version control
• unclear issue ownership
• weak prioritization
• disconnected workstreams
• late-stage committee narrative assembly

If the workflow is fragmented, the team only automates pieces of a slow process. That is why some AI deployments feel impressive in demo form but fail to shorten the real diligence cycle meaningfully.

The metrics that reveal the real problem

If a team wants to shorten diligence timeline, it should measure where time is actually being consumed.

Useful process metrics include:

• time from request to usable document
• percentage of documents arriving in final versus revised form
• time between issue creation and first reviewer decision
• time from specialist finding to executive visibility
• number of times the same issue is restated for different audiences
• number of open issues without attached source evidence

Those metrics make delay visible. Without them, teams often assume the problem is “the deal is complex” when the real problem is that the operating model forces repeated rework.

What a shorter diligence cycle should still preserve

There is a bad version of speed and a good version of speed.

The bad version removes review steps, pushes judgments too early, or accepts unsupported answers because the clock is tight. That is not timeline improvement. It is risk transfer.

The good version preserves five things:

• source visibility
• reviewer accountability
• cross-workstream coordination
• executive readability
• the ability to explain how the team reached its conclusion

McKinsey's M&A work is useful here because it frames AI as a way to expedite tasks, not eliminate judgment [McKinsey & Company, "Gen AI: Opportunities in M&A", May 21, 2024]. That is the right standard for timeline improvement more broadly: the process should move faster because less time is wasted, not because fewer serious questions are asked.

Where Sorai fits

Sorai is built to compress the timeline by keeping issues, evidence, reviewer status, and executive visibility in one operating record. That means the team spends less time rebuilding context and more time deciding what the findings actually mean.

The point is not simply to review documents faster. The point is to keep the financial, tax, legal, and pre-LOI record coherent enough that the process does not restart every time a new audience needs the answer.

The bottom line

M&A due diligence takes so long because most teams still run a multi-workstream, high-stakes review process across disconnected files, tools, and reporting formats. The hours are real, but too many of them are spent re-establishing context rather than making better decisions.

If the goal is to reduce the diligence timeline, focus on the operating system around the work: file readiness, shared issue tracking, live synthesis, evidence linkage, and continuity from pre-LOI into full diligence. That is where most of the delay actually lives, and that is where the best improvement usually comes from.

Sources cited

1. Boston Consulting Group, "The 2024 M&A Report: Deals Are Taking Longer to Close. How to Respond.", 2024
2. Bayes Business School, "Cautious M&A investors taking extra care with due diligence", 2024
3. Deloitte, "2025 GenAI in M&A Study", 2025
4. McKinsey & Company, "Gen AI: Opportunities in M&A", May 21, 2024
5. Bain & Company, "Looking Ahead to 2025: Preparing for What Comes Next", 2025

Author

Sorai Editorial

Editorial review team for Sorai's public diligence content

The editorial team translates public primary-source research and Sorai's workflow perspective into material designed for private equity, corporate development, and transaction advisory readers.

Why does due diligence take so long?

It usually takes so long because the process runs across disconnected files, workstreams, and reporting formats that force the team to rebuild context repeatedly.

What is the biggest cause of diligence delay?

The biggest cause is usually workflow fragmentation, not the raw analysis itself. Delays compound when document requests, issue tracking, and final synthesis live in separate places.

Can AI shorten the diligence timeline?

Yes, but only if it is attached to a better operating model. Deloitte reported that 86% of surveyed organizations have integrated GenAI into M&A workflows, but value still depends on whether the workflow itself is structured well enough to turn faster review into faster decisions [Deloitte, "2025 GenAI in M&A Study", 2025].

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