Virality is product-led growth where users bring in other users — through invites, sharing, or visible network participation — reducing reliance on paid acquisition.

How it works

Teams measure virality with the viral coefficient (K-factor):

• K = (invites sent per user) × (conversion rate of invites)
• K > 1 implies exponential self-propagation; K < 1 needs supplemental channels

Examples:

• Communication tools: each user adds teammates (Slack-style)
• Consumer apps: shareable content with watermark or referral credit
• Marketplaces: buyers pull sellers and vice versa

Loops have stages: trigger (why share), channel (how), and reward (why accept). Dropbox-style referral credits and Zoom meeting links are classic loop designs.

Virality rarely sustains alone at scale — saturation, churn, and channel fatigue drop K over time. Investors examine cohort retention alongside viral signup share to see if invited users stick.

Why it matters

• Founders: Design loops early — onboarding prompts, share mechanics, and incentives. Measure invite funnel separately from SEO or paid ads.
• Investors: High organic share with strong retention signals scalable GTM. Inflated “virality” from influencer spikes without retention is a pass.

Common mistake

Calling PR spikes or TikTok moments “virality.” True viral loops are repeatable in product analytics, not one-off traffic surges.

Related ideas

See also winner-take-most, network effects, and CAC.