Most transactions that miss their intended closing date don’t fail because of a genuine deal-breaking issue. They fail because due diligence stalls, and nobody catches the slippage early enough to fix it.
McKinsey research on major global acquisitions found that delays affected roughly 30% of the 50 largest deals tracked over the past two years, with an average delay of six months. Most deal teams set a closing target without building in the visibility or buffer needed to catch a slipping workstream before it threatens the whole schedule.
This article looks at what actually causes due diligence delays and how to build a due diligence timeline realistic enough to hold up once the process is underway.
Why due diligence timelines slip?
Due diligence is taking longer, and it’s not a fluke. A 2026 ION Analytics report, published in partnership with SRS Acquiom, found that one in five senior investment banking executives say their due diligence timelines have extended over the past two years, with 57% of that group reporting the process has added one to three months.
Behind that shift, three recurring patterns account for most of the slippage deal teams see:
- Unclear workstream ownership. When no one person is accountable for a given workstream, document requests and follow-up questions sit unanswered while each side assumes the other is handling it.
- Bulk document requests. Requests arriving all at once, instead of being organized into a prioritized list, create a bottleneck that reviewers can’t work through in order of priority.
- Unmanaged scope creep. Early findings often trigger additional workstreams or a deeper review than the original schedule assumed, and if that expansion isn’t tracked, it quietly eats into the time left before signing.
Each of these causes compounds the others. A missed request sits longer when ownership is unclear, and an unprioritized backlog makes it harder to tell which delays are routine and which threaten the due diligence schedule as a whole.
Setting a realistic timeline from the start
How long does due diligence take? A deal team should benchmark the answer to that question against deal size and complexity, not against a target date picked for other reasons. A schedule built backward from an arbitrary closing date rarely survives contact with the actual review.
A few practices make the resulting M&A deal timeline more durable:
- Benchmark against comparable deals. Use deal size, sector, and structural complexity (not the desired close date) to set the baseline.
- Build buffer around known bottlenecks. Specialized reviews, such as technical, environmental, or regulatory diligence, rarely move at the same pace as the rest of the workstreams, so plan for that in advance rather than assuming uniform progress.
- Agree on milestone checkpoints upfront. Both sides should sign off on interim checkpoints, not just a single closing date, so a slipping workstream is visible weeks before it becomes a crisis.
How platform choice affects due diligence timeline?
The specific data room for M&A that a deal team selects affects how quickly workstreams can move, since search, Q&A, and permission features determine how much reviewers can handle independently. A platform with weak search or a clunky permission structure pushes more coordination work back onto the deal team, slowing every workstream that depends on quick access to the right file.
Evaluating a platform for how well it supports independent reviewer work, not just for storage capacity and security certifications, is part of setting a realistic schedule in the first place. A tool that requires the deal team to manually route every request adds hours that a well-organized, self-service platform would have avoided.
The role of document organization in keeping pace
A structured, well-organized document request list prevents the back-and-forth that eats up the most time in a compressed due diligence timeline. When reviewers can locate what they need without asking, they stop depending on the deal team to answer routine requests, and that dependency is where a lot of delay quietly builds up.
Document organization directly affects pace for a simple reason: reviewers waiting on files they can’t find themselves become the bottleneck, no matter how well the rest of the process is structured. This is one of the clearest levers available for managing due diligence workstreams, because it’s within the deal team’s control from day one, unlike delays that originate on the counterparty’s side.
Managing scope creep without blowing the schedule
Not every finding that surfaces mid-process deserves the same response. Some need immediate escalation, while others can be logged and resolved without stalling the whole review. A deal team benefits from setting the distinction early rather than deciding case by case under time pressure.
A few habits help keep scope changes from quietly consuming the schedule:
- Separate escalation-worthy findings from routine ones. Define, in advance, what counts as significant enough to pause the process versus what gets tracked and resolved in the background.
- Set a clear threshold for a formal extension. Decide what triggers a real timeline change versus what gets absorbed into the existing buffer, so the decision isn’t made ad hoc.
- Communicate schedule impacts as soon as they’re identified. Flagging an impact early gives both sides time to adjust; flagging it after the original date has passed does not.
Weekly cadence and escalation that keep things moving
A standing weekly status check across all workstreams is one of the simplest ways to catch a stalled item before it threatens the close date. Reviewing progress on a fixed cadence, rather than reacting to problems as they surface, gives the deal team a consistent view of where the process actually stands against the plan.
Two habits make that weekly check more effective:
- Assign one escalation point on each side. A single, named contact resolves schedule-threatening issues faster than a request sitting in a shared inbox or email thread.
- Track outstanding items by age, not just by category. Sorting by how long a request has been open (not just what workstream it belongs to) surfaces the oldest unresolved items first, which are usually the ones closest to becoming a real due diligence delay.
Conclusion
Due diligence timelines slip most often due to unclear ownership, disorganized document requests, and unmanaged scope creep, not the inherent complexity of the review itself.
Deal teams that set a realistic schedule upfront, maintain weekly visibility into workstream progress, and address scope changes as they arise are far more likely to reach signing on the date they originally set. As deal volume and complexity continue to grow, treating timeline management as its own discipline, rather than an assumption baked into the closing date, has become a practical way to keep transactions on schedule.
