Check how many users your startup has. Let's say, you've just started and currently have 150 users.
Check how many invites/shares you have on average coming from a single startup user. Let's say, each user shares your startup offer with 30 friends. That would be 150 x 5 = 750 shares.
Now, how many of those people sign up for your startup offer (or do other desired action). Let's say, 250 people (33%) do it.
Now divide the number of new startup users by the number of users you started with and you will gain your Viral Coefficient: 250/150 = 1.7.
If you are interested in more specific and complicated approach or calculating Viral Coefficient over time, check out hybrid model and this example by David Skok.
While it might seem that viral growth is something random or totally in hands of influencers who share information about your startup with their audiences, actually even a new company creating something as unexciting and common as blenders, can go viral. For example, in 2006 Blendtec went viral (700% increase in sales!) thanks to a series of YouTube videos called "Will It Blend?" where company employees were blending glass marbles, iPhone and other objects with Blendtec to demonstrate product toughness. In 2016 Pokémon GO went viral with 9.55 million active players in US only!
People talk about what makes them look better, namely more successful and more smart. It is called "social currency", people exchange knowledge about your brand for social approval. Plus, we are all more open to recommendations from people we know than to advertising: friends and family won't recommend us a dating app if we're getting married while advertising is shooting at random.
Find your distinctive feature. Uber did it quite nicely: imagine telling someone for the first time that there's an app for hailing a cab with a simple touch! Product Hunt is collecting new best startups — who wouldn't like to be the first to discover the next Tinder?
Use gamification. Foursquare with its system of badges is probably the best example here. Also, airlines, such as American Airlines or British Airways are successfully implementing various loyalty problems with gamification elements — many people aren't even using those free miles but opt-in to enjoy the process of hunting for them and other offers.
Help people feel like insiders. Invite-only communities have been popular since the beginning of Internet. For example, SmartBargain, a website offering various sales wasn't doing very good until it became an invitation only shopping web-site.
According to "Contagious" book, American consumers mention brands over 3 billion times a day. That's why you need a strong trigger that will help your startup to come up in this kind of conversations. Triggers are stimuli that connect various actions and phenomena together. They play a key role in building habit-forming products. What you need to do is connect your startup with the right trigger from the environment your users live in.
Frequency. When KitKat was losing popularity, marketing team created a campaign that helped to promote it as a perfect candy to eat with coffee. Why coffee and not hot chocolate or tea? Well, tea isn't popular in US and hot chocolate is considered to be a winter drink.
Strong connection. It's quite hard to create a strong connection with red color since so many tech companies are already using it (YouTube, Netflix, Pinterest, etc.). But yellow is far less common and Snapchat made a wise move by using it.
Presence in the right location. There's no use if people suddenly remember that they should have built a route with your app that helps to find better roads when they're stuck in the middle of nowhere with no Internet access. Invest in creating triggers that work in places your startup can be used. For example, Netflix, is heavily triggered with weekend evenings you have no plans for or are too sick to go out.
Positive emotion causing high physiological activity: Parisian Love campaign advertising Google managed to show a love story through searches a person does in their search engine.
Negative emotion causing high physiological activity: BMW The Hire campaign was packed with fear and adrenaline demonstrating risks of hiring a car instead of owning one. BMW car sales grew 12% that year.
People need to see others using your app to start using it themselves. For example, Meerkat streaming app gained a lot of popularity during SXSW15 where people could see others using it to stream video to their friends and followers and were copying their behavior. Others publicly using your product is a social proof of its worthiness.
Brands selling consumer products often give away bags, cups, stickers and other merchandise their client's wear or use publicly. They serve as behavioral residue, a reminder about the product when it is not used. Do the same for your startup.
Even though the startup above actually needs money, it offers limited pledges to encourage investments.
On the higher level stories tell people about social norms and expected behavior.
On the lower level they might inform what app is better for finding a doctor.
Stories are questioned less often than advertising. After all, it is something that happened to a real person you might even know. And the drama and action make us less likely to disagree — we're too interested how it all ends to interrupt and question details.
Viral growth is not caused by special people, your product is the one who is responsible for it.
Viral popularity is available to everybody, tech and non-tech startups included. You should simply engineer your efforts the right way.
Six principles we discussed above help startups to increase their viral potential.
Too often brand marketing is focused on making people talk about the brand instead of focusing on what exactly they will be talking about. To make your startup shine create messages and viral stories that will be associated with your product to have valuable virality.