How do I know if someone new is lying?

Mostly, you can’t tell by watching someone, and the research says almost nobody can. What you can do is notice whether their story holds together over weeks, and check the few parts that matter to you against things you can actually see.

Why can’t you just tell?

Because the tells you’ve heard about (looking away, fidgeting, too much detail) don’t work. In a large review of 206 studies covering 24,483 judges, Charles Bond and Bella DePaulo found that people trying to spot lies in real time were right 54% of the time, barely better than guessing.1 People were better at recognizing truths (61%) than lies (47%), which means most of us lean toward believing what we hear.1

So how do lies actually come out? When Hee Sun Park, Timothy Levine and colleagues asked people about real lies they had uncovered, very few were caught in the moment from someone’s behavior.2 They came out later, through a friend who mentioned something, a receipt or a photo, a detail that didn’t match what the person already knew, or a confession.2

That’s good news, actually. It means you don’t need to become a human lie detector over dinner. You need time, and a life that overlaps with theirs a little more each month.

How much do people shade the truth on a profile?

Some, almost everyone, and mostly in small ways. In a study led by Catalina Toma, Jeffrey Hancock and Nicole Ellison, researchers measured the height, weight and age of 80 online daters in New York and compared them with their profiles.3 About 81% were off on at least one of the three, but usually by only a little.3 Men tended to add height, women tended to trim weight.3

Photos get the same polish. In a follow-up study of 54 online daters, the daters rated their own profile pictures as fairly accurate, but independent judges rated about a third of them as not accurate, often because the photo was older or retouched.4

So picture Renee, 46. She’s been seeing Mark for five weeks. His profile says 6’0”, and he’s maybe 5’10”. His photos are from a better haircut. None of that tells her much about whether he’s honest about the things that matter to her: whether he’s really single, whether he wants a relationship, whether his job and his kids are what he says. A polished profile is the normal background noise. The questions worth asking are about the life, not the photos.

Does being in your 40s change anything?

A little, and mostly in your favor.

In a study of 1,005 people aged 6 to 77, Evelyne Debey and colleagues found that how often people said they lied peaked in adolescence and dropped through adulthood, and that skill at lying peaked in young adulthood and declined after that.5 That’s an average across a lot of people, not a promise about the person across the table. But it’s a reason not to start from the assumption that everyone your age is running a game.

The bigger advantage is structural. At 25, a new person can be almost anyone. At 45, they usually come with a whole life: a job, maybe kids, an ex, a sibling who calls on Sundays, a house or a lease, friends from twenty years ago. A real life leaves traces, and those traces show up naturally over a few months if you’re both letting each other in.

The disadvantage is that you also come with a history. If your last relationship ended with a lie you didn’t see coming, your mind may now be scanning for the next one. That vigilance can make an ordinary slip (he got the date of his trip wrong) feel like a confession.

What’s worth checking, and what isn’t?

When something feels off, try separating four things before you react.

• What happened. Only what was said or done. “She said she’s been single a year. Tonight she mentioned a breakup in March.”
• The reading. What you think it means. “She lied about her timeline.”
• The fear. What it touches. “I’m being fooled again.”
• The next step. Something you can do. “Ask her, lightly, which it was.”

Then ask whether the thing actually matters. A trimmed age by a year or two? Probably not, and you’ll see the real one eventually. Whether they’re still living with an ex, still married on paper, or still dating three other people while saying they’re not? That matters, and you’re allowed to ask it plainly.

What tends to be useful over the first few months:

• Consistency over time. Do the stories about their week, their family and their past stay the same when they come up again?
• Overlap. Are you slowly meeting the people in their life, and are they curious about yours?
• Follow-through. Do small plans happen, or do they keep almost happening?

None of these tell you what’s in someone’s heart. They tell you whether their words and their life line up, which is the part you can see.

When is it bigger than a small fib?

Some patterns deserve a pause no matter how good the chemistry is: a person who always has a reason not to meet in person or on video, a life you never get any window into after months, or any request for money from someone you’ve known only a short time. Those aren’t puzzles to solve by reading them better. They’re reasons to slow down and talk to a friend you trust.

And if the checking has started to take over (you’re up at night cross-referencing things they said, or you can’t enjoy a single date), that’s worth attention for its own sake. If distrust is persistent and is spilling into your sleep, work or friendships, a licensed therapist is the right kind of help.

What the research doesn’t show

• Lie-detection studies mostly use strangers and short clips, not people who have been dating for months.
• The profile study measured height, weight and age, not the things most people actually worry about, like relationship status.
• The lifespan study is an average. It can’t tell you whether one particular person is honest.
• Survey answers about what’s ‘common’ on the apps are impressions, not counts.

What to do this week

• Play the sort above and notice which of your current worries landed in the Guess bin.
• Write down the one question that actually matters to you, the one about their life, not their photos.
• Ask it in daylight, in a calm moment. “You mentioned the paperwork isn’t final. Where are things, really?” is a fair question at month two.
• Listen for a simple answer. Honest answers are often a little boring.
• Let the next month do some of the work. Real lives show up over time. Give this one the chance to, or to not.