Viral Factor Basics

Quick hits on how to think about virality for your product

👋 Hey, I’m Ben! I write weekly about how to grow products and companies. I go deep on growth strategies, how to build products users love, and what actionable lessons can be learned from what best-in-class companies are doing and industry experts are saying.

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Happy Friday! 

Welcome to the first edition of my Brain Expansion Nugget (B.E.N.) series! This week I’ll be covering viral factor basics because, well, everybody wants their product to go viral. Explosive user growth without an explosive marketing budget? Sign me up! 

On this topic, I’ll be going through Adam Nash’s article on Viral Factor Basics. You can find his full article here if you want to go deeper and read the whole thing. 

Product virality occurs when people like your product so much that they tell other people about it without you asking them to. Virality can be measured through a metric called viral factor; I won’t go into the math for calculating a viral factor in this post, but I do want to share some thought-provoking questions and insights that can help you evaluate how to improve your products' virality.

Adam outlined three key questions to ask yourself about your product to get a sense of its virality:

• How can a user create content that reaches another user?

• How does a user’s experience get better the more people they are connected to?

• How does a user benefit from reaching out to a non-user?

You might be surprised at the answers to these questions for your product; I know I was the first time I asked them about mine. Facilitating user to non user touchpoints is a great way to spread word of mouth, even if those touchpoints don’t occur in the context of user acquisition. 

For example, if you are building a workout app, having an easy way to share a summary of the workout after completion could be an easy way to get exposure as your users share those summaries with friends via text, social media, Strava, etc. The context of this touchpoint isn’t your user saying “hey, you should use this app!” but it’s still driving exposure and awareness for your product, which is valuable.

Adam shares another valuable insight around virality:

The key to understanding viral math is to remember a basic truth about rabbits. Rabbits don’t have a lot of rabbits because they have big litters. Rabbits have a lot of rabbits because they breed frequently.

When you are trying to drive growth, it’s easy to focus on how many invites you can drive without considering the amount of time it takes to drive those invites. Adam goes on to put this in the form of the a simple equation:

Think of a basic exponential equation: X to the Y power.

• X is the branching factor, in each cycle how many new people do you spread to.

• Y is the number of cycles you can execute in a given time period.

If you have a cycle that spreads to 10 people, but takes 7 days to replicate, in 4 weeks you’ll have something that looks like 10^3. However, if you have a cycle that takes a day to replicate, even with a branching factor of 3 you’ll have 3^27. Which would you rather have?

In practice the impact of your viral message decays over time. Ideally you want to find the optimal combination of a high branching factor with a fast cycle time.

Here’s an example on how you could approach this: it’s not uncommon for the early part of a user’s lifecycle to be the point at which they are most likely to refer friends. You could set an offer where you incentivize users to refer X friends in Y period of time and then test different values of those variables. 

What ultimately drives the highest ROI? A promotion that rewards 1 referral in 7 days, 2 referrals in 15 days, 3 referrals in 30 days, or something else entirely? You’ll have to test and find out!

That’s all I’ve got for you for now. Until next week! 

- Ben

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