Holding onto friendship is hard, once families and more-demanding careers begin to weigh. But researchers have made a stab at pin-pointing the age at which our social circles start to contract, and it’s earlier than you might think: 25 is peak friend for both men and women, according to a study from the Aalto University School of Science in Finland and Oxford University’s Department of Experimental Psychology.

How many friends does any one person have? Obviously that’s a difficult question to answer—most people probably don’t know the answer about themselves with any accuracy. The researchers’ method was to analyze calls made from mobile phones within certain time periods, which ranged from a month to a full year. The call records were collected from one European mobile operator in 2007, and anonymized records were whittled down to 3.2 million users for whom both age and gender were available.

People of both genders called the most different people regularly—meaning at least once a month—at the age of 25.

Researchers noted that young men called more different people than young women, speculating that this reflects younger men’s search for sexual partners, which changed later in life.

But at another key age, women take over from men as having the most social contacts, and it remains that way into their 90s. That age is 39. By that time, most are calling just a small handful of others regularly: men call around 12 different people per month, and women around 15.

From around 45-55, friendship levels appear to plateau for both genders, but women still have more contacts than men.

Of course, not all the people we call are friends, and not all friendship includes phone calls. But the researchers say that their finding correlates with other studies in the ‘face-to-face’ world. Social media may well be changing friendship, but for now, a lot of it is still represented by calling up your friends and arranging to have coffee.

Cassie Werber/Quartz