Friendship Half-Life Calculator
Predict when friendships fade without contact and get a maintenance schedule.
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Friendships don't break — they fade. Without intentional contact, closeness decays exponentially. Research by Robin Dunbar shows we can maintain about 150 social connections, but only 5 are 'close friends' who require weekly or bi-weekly contact to stay in the inner circle. This calculator shows how quickly any friendship drops to acquaintance-level without contact, and builds a maintenance schedule to prevent it.
Example
Friend: college roommate
Decay Formula
Closeness(t) = Initial closeness × decay_rate^(weeks since contact) Decay rate ≈ 0.92 per week for close friends (contact weekly) Decay rate ≈ 0.96 per week for regular friends (contact monthly) Maintenance contact needed = when closeness drops below your threshold
The Friendship Decay Model
Dunbar's research shows friendship closeness decays by roughly half for every doubling of the interval between contacts. A friend you see weekly drops to 50% closeness after 2 weeks of no contact — not because either person is cold, but because the brain's social cache updates continuously. Shared experiences and emotional intimacy slow the decay; purely logistical contact (group chats, likes) barely slows it at all.
Frequently Asked Questions
Does texting count as maintaining a friendship?
Light texting slows decay slightly but doesn't reset it. Voice calls or video significantly outperform text. In-person resets the clock most completely.
How many close friendships can one person sustain?
Dunbar's number puts the close-friend limit at about 5. The next layer (good friends) holds about 15. Beyond that, relationships become more acquaintance-level.
Are childhood friendships harder to maintain as adults?
Yes — without shared daily environment (school, neighbourhood), contact requires intentional effort. The decay model still applies.
What's the minimum contact to maintain a strong friendship?
Research suggests meaningful contact (call, in-person) every 2–4 weeks preserves closeness for most people. Monthly is the floor for 'close friend' status.