Ask a room of angels how long they spend checking a deal and you'll hear everything from an afternoon to a fortnight. So how much is enough? The honest starting point is that almost nobody has the data to answer that, because the question has been measured properly exactly once.
This page isn't a guide to running diligence. Two pieces already cover that ground: our due-diligence checklist and the walk-through of how syndicates run it. What follows is narrower and, for a numbers-minded investor, more useful: the actual evidence on whether the hours change the result.
One study put a number on it. It's American, and it's from 2007.
The one dataset that puts a number on it
If you want a figure for how many hours of due diligence pay off, there is one source, and you should know its limits before you lean on it. Robert Wiltbank and Warren Boeker, writing for the Kauffman Foundation in November 2007, tracked 539 angels across 3,097 investments and 1,137 exits. It remains the only quantified study linking diligence hours to investment multiples.
Two caveats travel with every figure that follows. The data is American, and it is now well over fifteen years old. Angel groups in the US in the mid-2000s are not UK angels in 2026, and the market has changed around them. Treat the numbers as a signal about direction, not a current UK benchmark. Across the whole study, angels saw an overall return of about 2.6x in 3.5 years, roughly a 27% IRR. The median angel spent about 20 hours on diligence per deal.
What the numbers actually showed
In the Kauffman data, more diligence went with better outcomes, and the gap was large. Deals where the angel did under 20 hours of due diligence returned about 1.1x over 3.4 years, barely the money back. Deals with more than 20 hours returned about 5.9x over 4.1 years. At 40-plus hours, the figure rose to roughly 7.1x. Those are the Wiltbank/Kauffman bands, US, 2007.
Read that gap carefully. A jump from 1.1x to 5.9x is the difference between treading water and a serious win, and it lines up with crossing the study's 20-hour median. That is why the number gets quoted so often. It is also why it gets misquoted: the study does not say that 20 hours is a magic threshold, or that the 1.1x deals would have done better with more time. It says that, on average, the better-researched deals in this sample of US angels turned out far better. The arithmetic is real; the lesson is narrower than the headline.
What the UK evidence adds, and where it stops
Does the same hold for British angels? The closest UK read is Wiltbank's NESTA study from 2009, covering 158 UK angels and 406 exits. It found the same direction: angels who did more due diligence experienced fewer total failures. So the qualitative story carries across the Atlantic.
Here is the catch, and it matters. The UK study did not publish hours-to-multiple bands. There is no British 1.1x-versus-5.9x split to point to, only the direction. And nothing newer has replaced it. The British Business Bank's recent equity research has begun reporting on angel activity, but it covers sentiment and behaviour, not diligence effort against realised returns. So anyone citing a precise UK figure for the payoff of an extra ten hours is citing something that doesn't exist. The honest position is that the direction is corroborated for the UK and the magnitude is not.
Why more hours might track with better results
Correlation isn't a mechanism, so it's worth asking what the hours stand for. The likeliest reading is selection, not alchemy. Spending 30 or 40 hours on a deal usually means you got real access: management answered hard questions, you reached customers, you read the contracts rather than the deck. The hours are a proxy for engagement, reach and the chance to walk away from something that doesn't hold up.
On that reading, the angels doing more diligence weren't buying returns with time. They were finding more reasons to say no, and what survived the work was a stronger book. That fits the failure-rate finding in both studies: more checking, fewer total losses. It also sets the ceiling on the claim. If the hours are mostly a filter, then padding the clock on a deal you've already decided to do buys you little. The work has to be the kind that could still change your mind.
What this data does and doesn't tell you
What the evidence supports is modest and worth saying plainly: skipping diligence is associated, in the one study that measured it, with markedly worse outcomes, and the UK echo points the same way. What it does not do is set your number. It cannot tell you that your next deal needs 20 hours, or 40, or that a given startup is a good use of your capital. The bands are US, from 2007, and the UK has no quantified replacement.
This is general information, not financial advice, and it is not a steer toward or away from any investment. How much diligence a deal warrants depends on the deal, your experience and what you can actually find out, and the decision is yours to make or to take advice on. For the practical side, our checklist and the syndicate walk-through cover the how; if you're weighing software to speed the work, AI diligence tools sits alongside this. Before you commit capital, confirm the position with an FCA-regulated adviser.
Frequently asked questions
How many hours of due diligence should an angel do?
The most-cited data centres on about 20 hours per deal, the median in the Wiltbank/Kauffman study, but that is US data from 2007 and not a rule. In that study, deals with under 20 hours returned about 1.1x and deals with more returned far more, which is why 20 hours gets quoted as a rough floor. There is no UK figure for the right number of hours. Treat it as a signal that skipping the work tends to cost, not as a target. This is general information, not advice.
Does due diligence improve angel returns?
The data associates more diligence with higher returns and fewer total failures, but it is a correlation, not a guarantee. The Wiltbank/Kauffman 2007 study (US) found deals with over 20 hours of diligence returned about 5.9x against about 1.1x for under 20 hours. The NESTA 2009 study found the same direction for UK angels, fewer failures with more diligence, without publishing multiples. The likeliest explanation is selection: the hours are a proxy for access and judgement, and the work helps you avoid bad deals more than it rescues good ones.
Is there UK data on due diligence and returns?
Only partly. Wiltbank's NESTA study from 2009, covering 158 UK angels, found that more diligence was associated with fewer total failures, so the direction holds for the UK. But it published no hours-to-multiple bands, and nothing newer has replaced it. The British Business Bank's recent equity research covers angel activity and sentiment, not diligence effort against realised returns. So there is no current UK figure for the payoff of extra hours; the quantified bands are all US, from 2007.
Can you over-do due diligence?
Yes, at some point thoroughness trades against speed and access. Competitive rounds close, and an angel who takes weeks longer than the syndicate may lose the allocation or sour the relationship with the founder. The studies do not put a number on where useful diligence stops paying, so this is a judgement, not a finding. The point of the hours is to change your mind where the deal doesn't hold up, not to run the clock on a decision you have already made.
Is this page financial advice?
No. It is general information about what the research found on due-diligence effort and outcomes. It does not tell you how many hours to do, and it does not recommend backing or avoiding any company. Reliefs, returns and risks depend on your circumstances, and early-stage investments can lose all the money put in. Confirm the current position and take advice from an FCA-regulated adviser before committing capital.