How Zero Wins: Product Analysis of the Fasting Tracker

What is Zero?

Zero was created in 2016 by Kevin Rose (founder of Digg) as a personal side project. It has just one main button that the user presses to toggle between the start and end of his fast. It records and displays the amount of time the user fasted on each day in the past week.

Seriously? You’re going to write an entire product analysis on something that has basically the same functionality as the “Timer” tab in the default Clock app?


In my opinion, the brilliance of a product is not simply about what it does, but more importantly how it does it. As a product manager, I also see enormous commercial potential for Zero as I.F. moves from the “early adopter” stage to the “early majority” (h/t Geoffrey Moore, Crossing the Chasm).

Zero’s interface on watchOS.

Why I Love It

It is no easy feat to get 70k+ App Store reviews with an average rating of 4.8/5. Most reviews contain some variation of “It just works. Exactly what I needed.” They’re by passionate users writing to share their success stories (e.g. “lost the 15lbs I gained after back surgery”, “I feel so much better, VERY grateful!”)

So, why is Zero so popular?

In my view, it is because Zero embodies two product development principles that I highly value: Know Your Customer (KYC) and Keep It Simple, Stupid (KISS).

1. Zero intimately understands its users

There is no such thing as the perfect product for everyone. Since product managers are always making trade-offs (e.g. a feature might be highly demanded by some users but loathed by others), it’s vital that they meticulously define who Zero is for. Based on the design and engineering decisions manifested in the app, I believe that the target customer personas they had in mind are:

  • age 20 to 40,
  • working professionals,
  • living in coastal, health-conscious cities(e.g. New York, SF, LA, Seattle),
  • OINK (One Income, No Kids) or DINK (because skipping meals might be unacceptable/inconvenient when raising kids)

This general user profile can be segmented down to more specific sub-groups:

  • The “Rookie”: Newly graduated from the“unconvinced”camp, don’t want to be bothered by intricacies, adopted I.F. as a preventive measure or for longevity.
  • The “Patient”: Similar to the “Rookie”, but is already ill and adopted I.F. based on physician’s recommendation, more likely to comply in the long-term because more “skin in the game.”
  • The “Biohacker”: Deep into the quantified self rabbit hole, goes to extreme lengths to measure biometrics in order to optimise for physical or cognitive performance.

2. Zero prioritises simplicity while still accomplishing the “job to be done”

The above customer discovery might reveal to us that Zero’s core users:

  • A) disproportionally value design (tech-savvy, 0 patience for unintuitive UX), and
  • B) are willing to pay for it (high income, used to paying for subscription software).

“The main thing is to keep the main thing the main thing.”

Navigation is simple and only takes the user to one of these 3 views.

Zero’s simple, yet effective three-view design (“Setting”, “Home”, and “Science”) was no doubt a result of the first of these key insights. Upon opening the app, there is one obvious place for the user to click, that is the “Start/Stop Fasting” button. This enables the user to immediately fulfill the app’s main “job to be done” (h/t Clayton Christensen, The Innovator’s Dilemma).

The colour scheme of Zero also changes from orange to green to indicate whether the user is under or over his fasting goal. This is a best practice commonly found in the most well-designed apps (e.g. Robinhood’s interface changes from light to dark depending on whether the stock market is open).

The “Settings” page has only 3 options that can be adjusted, which limits decision fatigue (surely much appreciated by “hangry” users). Finally, the “Export Data” feature is included, but not emphasised because Zero understands that it is only really relevant to the aforementioned, niche “Biohacker” persona. The design of Zero removes all unnecessary distractions and places its core use case at the forefront.

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