How common are affairs in the UK? What twenty years and 1.5 million members reveal about who’s really cheating, when – and why the surveys undercount it.
There’s a question that surfaces at a certain point in every dinner party, usually somewhere between the second bottle and the cheese. Someone mentions a couple who’ve split up, someone else lowers their voice, and eventually somebody asks it: how many people do you think actually have affairs?
Everyone has a guess. Nobody has the faintest idea. And the people at the table who could answer from experience are, for obvious reasons, keeping quiet and passing the crackers.
We’re in an unusual position on this one. Illicit Encounters has been running for more than twenty years, with over 1.5 million British members – which means we’ve spent two decades watching who joins, when they join, and what they’re looking for. Put that alongside what the public research shows and you can get surprisingly close to an honest answer. The short version: affairs are more common than the surveys say, less chaotic than the films suggest, and a great deal closer to home than most people would like to believe.
The polite answer: about one in five
Ask British adults directly – anonymously, in a formal survey – and roughly one in five will admit to having been unfaithful to a partner at some point in their lives. That figure has proved remarkably stable across decades of polling. Some surveys put it a little lower, some closer to one in three, depending on how the question is worded and who’s doing the asking. But one in five is the number that keeps coming back, year after year, like a relative at Christmas.
Sit with that for a moment. One in five means that at any decent-sized wedding, a respectable handful of the guests nodding along to the vows have first-hand experience of bending them. It means your street has them. Your office almost certainly does. The school run is positively teeming.
And that’s just the people who said yes to a stranger with a clipboard.
Why the real number is higher than any survey will ever show
Here’s the structural problem with every infidelity statistic ever published: it relies on people being honest about the one subject they have organised their entire lives around concealing.
Researchers call it social desirability bias – the human habit of giving the answer that makes us look better, even on an anonymous form. And infidelity sits at the absolute top of the list of things people under-report. When studies switch from face-to-face interviews to computer-assisted ones, where no human being will see your answer, the number of people admitting to affairs reliably goes up. Same people. Same lives. Different willingness to say so.
Then add the definitional fog. The man three years into an intense, secret, daily messaging relationship with a woman from his old job doesn’t tick the box, because “nothing happened.” The woman who had six weeks of something electric on a work project in 2019 has filed it under “a strange time,” not under “affair.” Ask people if they’ve ever cheated and they reach for the narrowest possible definition, then answer no with a clear conscience.
So whilst the published figure is one in five, most researchers will concede the true lifetime number sits comfortably higher – somewhere between a fifth and a third of British adults. The honest answer to “how common are affairs?” is: more common than anyone says out loud, including to surveys.
Who’s actually having them? Closer to home than you’d think
The popular image is practically a stock photo: powerful man, younger colleague, expensive hotel. Twenty years of membership data tells a much less glamorous and much more interesting story.
The typical member of Britain’s biggest married dating site is in their mid-forties. They’ve been married somewhere between ten and twenty-five years. They have children, a mortgage, a Labrador or strong opinions about not getting one. They are teachers, NHS staff, accountants, engineers, people who run small businesses and people who run school bake sales. They are, in almost every measurable respect, the most ordinary people in Britain.
And here’s the detail that surprises outsiders most: the majority aren’t in marriages they’d describe as bad. They’re in marriages they’d describe as fine. Functional, co-operative, affectionate in a logistical sort of way – and missing something they’ve stopped being able to name. They’re not leaving. Most have no intention of ever leaving. What they want isn’t a different life; it’s a missing piece of this one.
Men vs women: the gap that quietly closed
For decades, every survey found the same comfortable pattern: men strayed, women endured. Men still admit to infidelity at higher rates than women in most polling – but the gap has been closing for years, and among the under-fifties it has narrowed to almost nothing. Whether that’s because women’s behaviour changed or because their honesty did is a genuinely open question. Probably both.
Our own membership settles the argument rather neatly: roughly 45% of our members are women. Not 10%. Not 20%. Forty-five. When the opportunity is discreet enough and the stakes are managed, women turn out to want broadly what men want, in broadly similar numbers – they’re simply better at not getting caught and considerably better at not telling pollsters.
Helen, 49, from Bristol, put it in a way we’ve never forgotten: “I didn’t want a different husband. I wanted about ten per cent of a different life. Nobody offers you ten per cent, so you have to arrange it yourself.”
When affairs happen: the seven-to-twelve-year window
Affairs cluster. They don’t arrive randomly across a marriage; they arrive at specific, predictable pressure points. The research and our own sign-up patterns agree on the big one: years seven to twelve. Deep enough into a marriage for the early voltage to have faded, early enough that you can remember exactly what you’re missing.
Around that window, the triggers are almost boringly consistent: a milestone birthday, a youngest child starting school, a parent dying, a partner who stopped asking questions somewhere around the second mortgage renewal. People don’t stray when everything collapses. They stray when everything settles.
We see it in the calendar, too. Our busiest week of the year, without fail, is the first full working week of January – new year’s resolutions cut in more directions than gym memberships. There’s a second surge every September, when families come home from the enforced proximity of the summer holiday and one or both partners returns to the office thinking: not another year like this one.
What 1.5 million members tell us that surveys never could
Surveys measure confession. A membership database measures behaviour – and behaviour is far more honest.
Behaviour says affairs in Britain are a midweek, daylight activity: site activity peaks on Tuesday and Wednesday and falls away sharply at weekends, when family life closes over people’s heads. Behaviour says discretion is taken seriously: password-protected photos are among the most-used features on the site, which rather punctures the idea of the reckless, devil-may-care cheat. And behaviour says the geography is upside down from the stereotype: per head, it’s not the big cities that over-index. It’s the market towns and the commuter belt – places with good rail links, long marriages and absolutely nothing to do on a Tuesday.
Assemble all of that and a picture emerges that almost nobody wants to put on a poster: infidelity in Britain is not a fringe activity carried out by damaged people in the dark. It is a quiet, careful, scheduled and deeply ordinary part of national life, conducted largely by people who also remembered to pick up the dry cleaning.
Does it actually matter how common it is?
Worth asking why anyone googles this question, because it’s rarely idle curiosity. In our experience it’s usually one of two people typing: someone who suspects their partner and wants to know the odds, or someone contemplating an affair themselves and wanting to know how much company they’d have.
If you’re the second person, here’s what the numbers can and can’t do. They can’t make the decision for you – that one’s yours, and it deserves more thought than a statistic. But they can dissolve the loneliness of it. The feeling that wanting more makes you uniquely greedy or uniquely broken simply doesn’t survive contact with the data. You are, awkwardly for the dinner party, somewhere in the statistical mainstream of human behaviour – and you’d be amazed who else is in there with you, passing the crackers.
Frequently asked questions
What percentage of married people cheat in the UK? Roughly one in five British adults admit to infidelity in anonymous surveys, with some polls running closer to one in three. Because people under-report – to researchers and to themselves – the true lifetime figure is widely accepted to be higher than the published one.
Who cheats more, men or women? Men still admit to it more, but the gap has narrowed dramatically, and among under-fifties it’s close to even. Our own membership is roughly 45% female – which suggests the difference was always more about discretion and disclosure than desire.
What’s the most common age to have an affair? The mid-forties, typically within a marriage of ten to twenty-five years. The highest-risk window is years seven to twelve of a marriage, often triggered by a milestone birthday, a bereavement, or a child starting school.
How many affairs are ever discovered? Nobody can count what was never found, but the balance of evidence suggests most affairs are never confirmed. When they are, it’s rarely a dramatic discovery – it’s usually a slow accumulation of changed behaviour that a partner eventually names.
Are affairs more common now than in the past? The behaviour itself appears remarkably stable across generations. What’s changed is opportunity and honesty: dedicated discreet platforms moved affairs online, and modern surveys catch more admissions. The internet didn’t invent the affair. It organised it.
One last number
However common affairs turn out to be, yours – should you ever have one – only needs to happen once, and well. Twenty years of helping Britain’s quietest statistics stay that way has taught us exactly what careful looks like.
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