Diligence Is Getting Longer, Not Deeper

A decade ago, the average deal spent about four months in due diligence. Today it's closer to seven.

The numbers come from SS&C Intralinks and Bayes Business School, who studied more than 900 transactions: the average pre-announcement diligence period stretched from 124 days to 203 days. And it's accelerating – deals done before 2020 averaged 189 days; deals between 2020 and 2022 ran to 247. Private targets now sit in diligence for around 234 days against 125 for public ones.

The easy read is that diligence has gotten more thorough. More time, more scrutiny, safer deals. I think that read is wrong, and the gap between "longer" and "deeper" is exactly where deals are quietly breaking.

Time is not the same as depth

More days on the calendar only means more protection if the added time is buying more rigor in the places that matter. The evidence says it often isn't.

SRS Acquiom's 2026 study found 73% of dealmakers expect diligence to keep getting more complex – and that technology diligence is now the single most burdensome element of the entire review, for 51% of them. That tells you where the extra time is going. Tech and cyber review have expanded to fill a large share of the calendar, and reasonably so; they're real risks. But attention is finite. When one workstream balloons, another gets less senior focus, and the one that tends to lose is the financial work – the quality-of-earnings scrutiny where, the dead-deal data suggests, transactions actually live or die.

So the picture isn't "diligence got deeper everywhere." It's "diligence got longer, and the new length went disproportionately into one workstream while the most deal-critical one got squeezed." A 247-day diligence that under-examines earnings quality is not safer than a 124-day one that nailed it. It just costs more and feels more thorough.

The honest counterpoint

There's a finding that seems to cut the other way, and it's worth meeting head-on. One 2026 analysis of UK deals found that transactions where diligence ran longer than three months had roughly a 15% higher chance of post-close value capture. Doesn't that argue longer is better after all?

It argues that depth is better, and depth takes time – which is not the same claim. The deals that did well weren't rewarded for sitting on the calendar. They did well because the time bought genuine scrutiny: cultural fit examined, earnings pressure-tested, risks actually surfaced. Time is a necessary input to depth, not a substitute for it. The failure mode I'm describing is the deal that spends all 247 days and still doesn't get the financial workstream the senior attention it needed. Long and shallow is the worst of both – maximum cost, minimum protection.

Buy depth, not calendar

For anyone supporting a transaction, the move isn't to compress diligence or to extend it. It's to make sure the length is buying depth where depth pays.

Protect the financial workstream's senior attention. As tech and cyber reviews expand, the quality-of-earnings work can quietly become a junior exercise. That's backwards. The most deal-critical analysis deserves the most experienced eyes, regardless of how loud the other workstreams get.

Treat synthesis as the deliverable, not collection. Longer diligence generates more documents, not more understanding. The risk that kills a deal is rarely one smoking-gun file – it's a pattern across many that only surfaces when someone capable connects them. More time spent collecting is not more insight. Time spent synthesizing is.

Ask what each added week is actually buying. If diligence is running longer, the question to put to the team is specific: what depth did the extra time purchase, and in which workstream? "We're being thorough" is not an answer. "We re-ran the add-backs and found three that recur" is.

The deal that breaks after a seven-month diligence didn't fail for lack of time. It failed because the time went somewhere other than the truth that mattered. Longer was never the goal. Deeper was – and they stopped being the same thing a while ago.