Viral coefficient

Viral coefficient is the average number of new users each existing user brings in through invites or referrals. Mixpanel notes that a coefficient above one means the product is growing on its own. Below that line, referrals still add users on top of your other channels, but each round of invites produces a smaller round than the one before.

How to calculate it

The formula is: viral coefficient = invites sent per user × conversion rate of those invites. In Waitlister's example, each user sends 5 invites and 20% of them convert, so the coefficient is 5 × 0.2 = 1.0.

LaunchList splits the invite side into two levers: the share rate, meaning the percentage of subscribers who actually share their link, and the conversion rate of those shared links. You need both numbers to know which one to work on.

What numbers to expect

LaunchList puts most pre-launch waitlists between K=0.2 and K=0.6. Waitlister reports that B2B waitlists typically see 0.3 to 0.7, while consumer products can reach 1.5 to 2.0. It cites Dropbox at 0.7 to 1.0.

Common mistakes

• Planning around a coefficient above one. LaunchList calls K above 1 rare and says it almost always takes a remarkable product and a sharp incentive. Build your forecast on a lower number.
• Working only on conversion. LaunchList finds that raising share rate by 10 percentage points usually does more than raising conversion rate by the same amount. Start with prompts and incentives that get more people to share.
• Writing off a low number. Mixpanel says most product-led products run below one, and that virality still lowers customer acquisition cost.
• Checking it once. Waitlister suggests tracking it weekly, so you can see whether a change to the referral flow moved either lever.

When it matters to you

It matters most when you are about to launch a waitlist or a referral program and need to decide whether invites can carry part of your acquisition plan. Pull share rate and invite conversion from your current data this week. Multiply them, then choose the weaker lever to test first. The referral program playbook and the waitlist launch playbook cover the setup. The growth loops guide shows where invites fit next to your other channels.