The Science of Friendship: What Research Tells Us

1. Time together matters

Jeffrey A. Hall studied the development of new friendships among adults who had recently moved and first-year university students. In both studies, more time spent together was associated with greater friendship closeness.

The study became widely known for estimates of roughly 50 hours to move from acquaintance to casual friend, around 90 hours to reach friend status, and more than 200 hours for a close friendship.

These figures are not universal thresholds. They are estimates from particular samples and do not show that accumulating a set number of hours automatically produces friendship.

In practice: do not treat hours as a quota. Look for realistic opportunities to see people again when there is mutual warmth and interest.

Source: Hall, J. A. (2019). How many hours does it take to make a friend? Journal of Social and Personal Relationships, 36(4), 1278-1296. DOI

2. What you do with that time matters too

In the same research, Hall found that time spent in leisure activities was associated with friendship closeness. Some forms of everyday conversation also predicted changes in closeness.

Time alone is therefore not the whole story.

In practice: a setting that allows genuine interaction is likely more useful than simply accumulating hours in the same place.

Source: Hall (2019).

3. Proximity creates more opportunities for friendship

One of the longest-standing findings in social psychology is the role of proximity: we are more likely to develop relationships with people we encounter regularly.

More recent work continues to find this effect. A 2022 longitudinal study found that children seated near one another in classrooms were more likely to become friends over time.

This study involved children, not adults, so it should not be mechanically generalized. But it offers an unusually clear demonstration of how the structure of an environment can create opportunities for relationships.

In practice: if you want to meet potential friends, a recurring environment can be more useful than a series of one-off events where you never see the same people again.

Source: Faur, S. & Laursen, B. (2022). Classroom Seat Proximity Predicts Friendship Formation. Article

4. Repetition helps, but it is not enough

Seeing someone repeatedly increases opportunities for interaction and familiarity. It does not guarantee friendship.

The classroom proximity study is useful because the children were already familiar with their classmates. Changes in seating still predicted new friendships, suggesting that opportunity and interaction matter beyond simple exposure.

In practice: keep showing up, but do not confuse repeated presence with a relationship. At some point, interaction has to happen.

Source: Faur & Laursen (2022).

5. More personal conversation can create greater closeness

In Arthur Aron and colleagues' classic experiment, strangers spent about 45 minutes answering questions that gradually encouraged more personal self-disclosure. They reported greater closeness afterward than participants assigned to small-talk tasks.

The experiment tested the creation of interpersonal closeness in a controlled setting. It did not show that the procedure guarantees a durable friendship.

In practice: conversation can become gradually more personal when comfort and reciprocity are present. You do not need to begin with an intensely intimate disclosure.

Source: Aron, A., Melinat, E., Aron, E. N., Vallone, R. D. & Bator, R. J. (1997). The Experimental Generation of Interpersonal Closeness. Personality and Social Psychology Bulletin, 23(4), 363-377. DOI

6. The other person's response matters

Research on adult friendship connects relationship quality with trust, support and self-disclosure. A systematic review of 38 studies also highlights supportive responses and reactions to a friend's attempts to share positive experiences.

Closeness is therefore not only about what one person reveals. It also depends on how the other person receives and responds to it.

In practice: listen, ask a question, show that you understood, and remember what matters to the other person. Friendship develops in both directions.

Source: Pezirkianidis, C., Galanaki, E. & Raftopoulou, G. (2023). Adult friendship and wellbeing: A systematic review with practical implications. Frontiers in Psychology, 14, 1059057. DOI

7. Reciprocity is central to friendship

Adult friendship is commonly described in the literature as voluntary and reciprocal. Social-network research also shows that perceived friendship is not always reciprocated and that reciprocated relationships differ from unreciprocated nominations.

That does not mean every message, invitation or favor must be returned immediately in identical form.

In practice: look at the pattern over time. Does the other person sometimes initiate, respond, accept or suggest another time, remember you, and make room for the connection? Reciprocity is better understood as two-way movement than exact accounting.

Sources: Pezirkianidis et al. (2023); Vaquera, E. & Kao, G. (2008). Do You Like Me as Much as I Like You? Friendship Reciprocity and Its Effects on School Outcomes among Adolescents. Article

8. Friendships need maintenance

Debra Oswald, Eddie Clark and Cheryl Kelly identified four broad friendship-maintenance behaviors: positivity, supportiveness, openness and interaction.

This matters because it moves the question from simply finding friends to what people do to keep a friendship alive.

In practice: maintenance can be ordinary: check in, make a plan, encourage someone, share what is happening in your life, and create another chance to spend time together.

Source: Oswald, D. L., Clark, E. M. & Kelly, C. M. Friendship Maintenance: An Analysis of Individual and Dyad Behaviors. Journal of Social and Clinical Psychology, 23(3), 413-441. DOI

9. Friendship quality matters for wellbeing

A 2023 systematic review examined 38 studies of adult friendship and wellbeing. Overall, friendship quality and socializing with friends were positively associated with different dimensions of wellbeing.

The authors also emphasize important limitations: much of the literature is cross-sectional, and many samples involve university students or younger adults.

In practice: having many friends and having satisfying friendships are not the same thing. Number alone gives an incomplete picture of friendship life.

Source: Pezirkianidis et al. (2023).

10. Reliable friendship is associated with lower loneliness

A longitudinal study following 346 people from age 20 to age 30 examined several dimensions of best-friendship quality, including intimacy, reliable alliance and conflict. Perceiving a best friendship as reliably supportive was associated with higher self-esteem and lower loneliness.

This does not by itself establish that friendship caused those outcomes, but it reinforces the importance of perceived quality and reliability.

Source: Langheit, S. et al. (2024). Links Between Best-Friendship Quality and Well-Being From Emerging to Established Adulthood. Article

11. Major life events reshape social networks

A meta-analysis of 277 studies examined changes in social networks across the lifespan. Networks change with age and with life events such as entering work, becoming a parent and widowhood.

This helps explain why moving, changing jobs, separating, or having a child can alter friendship life without any friendship necessarily having "gone wrong."

In practice: after a transition, it may help to deliberately rebuild structures of repetition: a weekly activity, neighborhood routine, sport, group, volunteering, class or recurring plan.

Source: Wrzus, C., Hänel, M., Wagner, J. & Neyer, F. J. (2013). Social network changes and life events across the life span: a meta-analysis. Psychological Bulletin, 139(1), 53-80. PubMed

12. Transitions can also create new opportunities for friendship

Transitions do not only weaken existing ties. They can expose us to new people.

Longitudinal work on young adults moving away from home for university shows that major changes in circumstances can create opportunities to acquire new friends while changing the composition of an existing network.

In practice: a new city or job is not only a loss of network. It is also a period when social routines are still being built.

Source: Kempnich, M. et al. (2024). PubMed

13. People often form friendships with similar others

Social-network research has long documented homophily: social ties occur disproportionately among people who share certain characteristics, circumstances or interests.

That should not be turned into the claim that the best friends are the people most similar to us. Similarity can make interaction or identification easier, while strong friendships can obviously cross many differences.

In practice: a shared interest or context can be a useful starting point. It does not need to become a total-compatibility test.

Source: Block, P. & Grund, T. (2014). Multidimensional Homophily in Friendship Networks. Article

14. Adult friendship is more than a numbers game

Research does not support one ideal number of friends for everyone. Adults themselves distinguish between levels of closeness, and research on wellbeing points repeatedly to quality, support, satisfaction and maintenance.

In practice: instead of only asking "Do I have enough friends?", a more useful question may be: "Do my current relationships offer the kind of closeness, support and reciprocity I need?"

Source: Pezirkianidis et al. (2023).

15. Science describes probabilities, not a friendship recipe

None of this research can guarantee that a particular person will become your friend.

Time together creates opportunity. Proximity makes repeated encounters easier. Personal disclosure can foster closeness. Reciprocity and maintenance support relationships. Life transitions reshape networks.

But friendship remains a voluntary relationship between two people. Context, personality, age, culture, life stage and mutual interest all matter.

That is the distinction The Friendship Practice tries to preserve: use research as a guide, then return to the real relationship in front of you.

Source: Synthesis of the research cited on this page.

What the research does not allow us to claim

"It takes exactly 200 hours to become close friends."

No. Hall's figures are estimates from particular samples, not universal biological thresholds.

"Seeing someone often is enough to become friends."

No. Proximity creates opportunities. It does not guarantee affinity or reciprocity.

"You should disclose personal things quickly to create connection."

No. Aron's experiment used gradual disclosure in a specific setting. Disclosure that is too intimate, badly timed or unreciprocated can be uncomfortable.

"The more friends you have, the better."

That is too simplistic. Relationship quality is a central dimension in the friendship and wellbeing literature.

"If a friendship takes effort, it is a bad friendship."

No. Friendship-maintenance research specifically shows that ongoing relationships involve behaviors that keep the bond active. Effort is not automatically imbalance.

How I select the research on this page

I prioritize peer-reviewed research, systematic reviews and meta-analyses when available, longitudinal studies when the question concerns change over time, and experiments when they offer a more direct test of a mechanism, rather than press summaries.

I also distinguish association from causation. Much friendship research is observational: it can show that two things are related without proving that one necessarily produces the other.

The literature also has limitations. Many studies have been conducted with university students, adolescents, or within a limited number of countries. A robust finding in one population should not be turned into a universal claim about every friendship.

Last reviewed: August 19, 2026

Sources

Key sources

1. Hall, J. A. (2019). How many hours does it take to make a friend? Journal of Social and Personal Relationships, 36(4), 1278-1296. https://doi.org/10.1177/0265407518761225
2. Aron, A., Melinat, E., Aron, E. N., Vallone, R. D. & Bator, R. J. (1997). The Experimental Generation of Interpersonal Closeness. Personality and Social Psychology Bulletin, 23(4), 363-377. https://doi.org/10.1177/0146167297234003
3. Oswald, D. L., Clark, E. M. & Kelly, C. M. Friendship Maintenance: An Analysis of Individual and Dyad Behaviors. Journal of Social and Clinical Psychology, 23(3), 413-441. https://doi.org/10.1521/jscp.23.3.413.35460
4. Pezirkianidis, C., Galanaki, E. & Raftopoulou, G. (2023). Adult friendship and wellbeing: A systematic review with practical implications. Frontiers in Psychology, 14, 1059057. https://doi.org/10.3389/fpsyg.2023.1059057
5. Wrzus, C., Hänel, M., Wagner, J. & Neyer, F. J. (2013). Social network changes and life events across the life span: a meta-analysis. Psychological Bulletin, 139(1), 53-80. https://pubmed.ncbi.nlm.nih.gov/22642230/
6. Faur, S. & Laursen, B. (2022). Classroom Seat Proximity Predicts Friendship Formation. https://pmc.ncbi.nlm.nih.gov/articles/PMC9113197/
7. Vaquera, E. & Kao, G. (2008). Do You Like Me as Much as I Like You? Friendship Reciprocity and Its Effects on School Outcomes among Adolescents. https://pmc.ncbi.nlm.nih.gov/articles/PMC2352147/
8. Block, P. & Grund, T. (2014). Multidimensional Homophily in Friendship Networks. https://pmc.ncbi.nlm.nih.gov/articles/PMC4267571/
9. Langheit, S. et al. (2024). Links Between Best-Friendship Quality and Well-Being From Emerging to Established Adulthood. https://pmc.ncbi.nlm.nih.gov/articles/PMC11196206/
10. Kempnich, M. et al. (2024). Research on changes in egocentric networks during the transition away from home to college. https://pubmed.ncbi.nlm.nih.gov/39079231/

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Related reading: How to make friends as an adult, Why making friends as an adult is hard, the Friendship Tracker, or browse all friendship guides.