Zero
Zero tracks fasting windows with a real-time timer across multiple intermittent fasting protocols, while adding mood journaling, weight tracking, body milestone notifications, hydration goals, meal photo logging, and an expert content library to support consistent fasting habits.
Start your fast with one tap — and let the science tell you exactly what your body is doing while you wait.
Zero is an intermittent fasting app developed by Zero Longevity Science, Inc. It is widely regarded as the most popular dedicated fasting tracker available, having appeared in coverage by the Joe Rogan Experience, Men’s Health, Women’s Health, and Fortune. The app is built around the premise that fasting is one of the most accessible tools for improving body composition and metabolic health, and that the main barrier for most people is consistency — not knowledge.
The core of the app is a single-tap fasting timer that tracks the active fasting window in real time across protocols including 16:8, 18:6, 20:4, circadian fasting, and custom intervals. As time progresses, the Fasting Zones system notifies users of physiological milestones — including when glycogen stores begin depleting, when fat burning increases, and when cellular autophagy typically begins — giving context that makes the discomfort of fasting feel purposeful.
A free version covers the core timer, basic statistics, a mood and reflection journal, and a content library of articles and educational material. The Zero Plus subscription at $69.99 per year adds an extended expert content library of videos, audio, and Q&As, advanced analytics, Fasting Zones, challenges, and now includes AI-powered meal photo logging and a personalized protein tracking goal.
Apps are frequently updated and may change over time. While we aim to keep our reviews accurate and up to date, some information may become outdated or no longer reflect the current version.
Disclaimer ▽ (click open)
How to Use
Getting started with Zero begins with a brief questionnaire covering eating habits, health goals, and lifestyle. The app uses this to suggest a fasting protocol — most beginners are directed to 16:8 (fasting for 16 hours, eating within an 8-hour window) — and creates a personalised starting plan. Users can change or customise their protocol at any time.
Starting a fast requires a single tap on the central timer. The timer counts up through the fast in real time, and the Fasting Zones display shows which physiological phase the body is currently in: Anabolic (0–4 hours), Catabolic (4–6 hours), Fat Burning (6–16 hours), and Ketosis (16+ hours). Each zone includes a brief explanation of what the body is doing at that stage. Notifications can be set to alert when zone transitions occur or when the fasting target is reached.
After breaking a fast, users can log a mood and energy reflection noting how the fast felt — whether it was easy, hard, or disrupted — and these entries are graphed over time to reveal patterns. A weight log tracks progress toward a goal weight. The statistics dashboard shows average fasting length, streak history, and longest fast. Streak tracking and achievement badges provide motivational feedback for consistency.
On Zero Plus, meal photo logging estimates calories and protein from a photograph. The Protein Score tracks a personalised daily protein target. The hydration tracker sets a daily water goal and logs intake. Apple Health and Google Fit sync weight, sleep, and activity data. An expert content library provides videos, audio segments, and articles from fasting and longevity researchers.
Strongest Points:
✓ Single-tap fasting timer with real-time Fasting Zones that explain exactly what the body is doing during each phase of the fast — from glycogen depletion through fat burning to autophagy
✓ Clean, low-friction design that removes all unnecessary steps between the decision to fast and starting the timer, making daily use genuinely effortless
✓ Expert content library with articles, videos, audio, and Q&As from leading fasting and longevity researchers, providing one of the most comprehensive educational resources in any health app
✓ Streak tracking, achievement badges, and challenges provide strong motivational feedback for users who benefit from visual consistency rewards
✓ Free plan preserves the core timer, statistics, journal, and content library — giving genuine value without requiring a subscription for casual or beginner users
Weaker Points:
✕ Zero Plus at $69.99 per year is relatively expensive compared to competing fasting apps, and some users feel the premium content does not justify the annual cost
✕ Free trials convert automatically to paid subscriptions, and some users have reported being charged without clear awareness of the conversion date
✕ The app does not provide medical or clinical guidance — the Fasting Zones are educational rather than personalised, and the app explicitly states it is not a diagnostic or medical tool
✕ Google Fit sync has been reported as intermittently unreliable by some Android users, which can cause gaps in health data correlation
✕ The recent addition of meal logging and protein tracking has made the app broader but means it now competes in areas where dedicated nutrition apps have significantly more depth and accuracy
How to Use
Getting started with Zero begins with a brief questionnaire covering eating habits, health goals, and lifestyle. The app uses this to suggest a fasting protocol — most beginners are directed to 16:8 (fasting for 16 hours, eating within an 8-hour window) — and creates a personalised starting plan. Users can change or customise their protocol at any time.
Starting a fast requires a single tap on the central timer. The timer counts up through the fast in real time, and the Fasting Zones display shows which physiological phase the body is currently in: Anabolic (0–4 hours), Catabolic (4–6 hours), Fat Burning (6–16 hours), and Ketosis (16+ hours). Each zone includes a brief explanation of what the body is doing at that stage. Notifications can be set to alert when zone transitions occur or when the fasting target is reached.
After breaking a fast, users can log a mood and energy reflection noting how the fast felt — whether it was easy, hard, or disrupted — and these entries are graphed over time to reveal patterns. A weight log tracks progress toward a goal weight. The statistics dashboard shows average fasting length, streak history, and longest fast. Streak tracking and achievement badges provide motivational feedback for consistency.
On Zero Plus, meal photo logging estimates calories and protein from a photograph. The Protein Score tracks a personalised daily protein target. The hydration tracker sets a daily water goal and logs intake. Apple Health and Google Fit sync weight, sleep, and activity data. An expert content library provides videos, audio segments, and articles from fasting and longevity researchers.
Strongest Points:
✓ Single-tap fasting timer with real-time Fasting Zones that explain exactly what the body is doing during each phase of the fast — from glycogen depletion through fat burning to autophagy
✓ Clean, low-friction design that removes all unnecessary steps between the decision to fast and starting the timer, making daily use genuinely effortless
✓ Expert content library with articles, videos, audio, and Q&As from leading fasting and longevity researchers, providing one of the most comprehensive educational resources in any health app
✓ Streak tracking, achievement badges, and challenges provide strong motivational feedback for users who benefit from visual consistency rewards
✓ Free plan preserves the core timer, statistics, journal, and content library — giving genuine value without requiring a subscription for casual or beginner users
Weaker Points:
✕ Zero Plus at $69.99 per year is relatively expensive compared to competing fasting apps, and some users feel the premium content does not justify the annual cost
✕ Free trials convert automatically to paid subscriptions, and some users have reported being charged without clear awareness of the conversion date
✕ The app does not provide medical or clinical guidance — the Fasting Zones are educational rather than personalised, and the app explicitly states it is not a diagnostic or medical tool
✕ Google Fit sync has been reported as intermittently unreliable by some Android users, which can cause gaps in health data correlation
✕ The recent addition of meal logging and protein tracking has made the app broader but means it now competes in areas where dedicated nutrition apps have significantly more depth and accuracy
Use it For:
🕒 Beginners starting intermittent fasting who want a clean, guided timer experience with protocol suggestions, educational content, and just enough structure to build a consistent habit
🧠 People who want to understand the science of fasting as they practise it — the Fasting Zones and expert content library make Zero one of the most educational fasting apps available
🏆 Users motivated by streaks, badges, and challenges who respond well to gamification and social accountability as tools for consistency
🔍 Anyone doing extended fasts (24+ hours) who wants real-time physiological context and motivational milestones to track progress through a longer fasting window
📱 Apple Watch users who want to check their fasting timer and end a fast directly from their wrist without picking up their phone
App Usable on:
Phone
Tablet
PC
TV
Applications and Features
Zero’s fasting timer is the centrepiece of the experience. It operates across multiple protocols — 16:8, 18:6, 20:4, 24-hour, circadian rhythm fasting, and fully custom intervals — with a real-time countdown displayed on the home screen and available on Apple Watch for quick-glance checking without opening the phone. The Fasting Zones system, available on Zero Plus, divides the fasting window into four physiological phases and provides contextual explanations of what the body is doing in each — a feature users consistently describe as one of the most motivating aspects of the app, because it turns passive waiting into a sense of active biological progress.
The mood and reflection journal prompts a brief check-in after each fast, asking the user to rate their energy level, hunger intensity, and how the fast generally felt. These responses are graphed over time and correlated with fasting length and timing data, surfacing patterns such as whether longer fasts consistently produce better or worse mood outcomes for a given user.
The expert content library includes videos, audio segments, articles, and Q&As from researchers in fasting, longevity, metabolic health, and nutrition. Zero Plus users get access to the full library; free users see a curated subset. Challenges allow users to join structured fasting goals, compare progress with friends, and unlock achievement badges. The Protein Score and meal photo logging, added in 2025, track daily protein intake against a personalised target based on weight and goals, with AI estimation from meal photographs.
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App Summary
Zero works because it focuses on one thing first and does it extremely well: making it dead simple to start and track a fast. The single-tap timer, Fasting Zones, and streak system address the three core reasons most people struggle with intermittent fasting — forgetting to start, losing motivation during the fast, and breaking streaks without understanding the consequences.
The expert content library is a genuine strength that separates Zero from most competitors. Having high-quality articles and video content from fasting and longevity researchers embedded directly in the app means users can learn while they fast rather than searching separately for credible information. For users who want to understand why they are fasting, not just track that they are, this is a meaningful advantage.
The $69.99 annual price for Zero Plus is the main point of debate. For committed fasters who use the content library and advanced features regularly, it is justified. For users who just need a reliable fasting timer and basic streak tracking, the free version — or a cheaper alternative — may serve them just as well.
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Zero is free to download, with the core fasting timer, basic statistics, reflection journal, and a curated content library available at no cost. Zero Plus costs $69.99 per year or $9.99 per month, unlocking Fasting Zones, the full expert content library, advanced analytics, challenges, AI meal photo logging, and the Protein Score. A free trial is available but converts automatically to a paid subscription unless cancelled before the trial end date — worth noting before signing up.
Learning Difficulty:
Zero is designed for complete beginners — the entire core experience is a single tap to start a fast, and the initial questionnaire sets a suitable protocol without requiring any prior knowledge of intermittent fasting.
Required Skill Sets:
Zero requires no prior knowledge of fasting, nutrition, or health tracking — the app guides new users through protocol selection and the fasting process from their very first session.
Educational Content:
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1/4
Questions & Answers: ⮛ (click to open)
Is Zero actually free, or does it force a subscription?
Zero has a genuine free version that includes the core fasting timer, basic statistics, a mood and reflection journal, and a curated subset of the content library. Zero Plus is an optional premium upgrade. The free trial that appears on first download converts automatically to a paid subscription unless cancelled, which has caused confusion for some users — but the free tier itself is available without any payment once the trial screen is navigated past.
What is the 16:8 fasting protocol and is it right for beginners?
16:8 means fasting for 16 hours and eating within an 8-hour window each day. For most beginners, this is easier to maintain than it sounds — if the eating window runs from noon to 8pm, the fasting window largely overlaps with sleep. Zero recommends 16:8 as the standard starting protocol for most users because it produces metabolic benefits while remaining practical for everyday social eating.
What are Fasting Zones and how accurate are they?
Fasting Zones are educational markers that appear on the timer as the fast progresses, indicating the general physiological phase the body is in at that point — for example, the transition from glucose burning to fat burning, or the period when cellular autophagy is thought to be elevated. They are based on average research data and are not personalised to the individual user’s metabolic state, diet history, or fitness level. The exact timing of these transitions varies considerably between people.
Can Zero replace a calorie tracking app?
Not fully. Zero’s meal photo logging and Protein Score provide a basic picture of nutrition, but the feature is focused on protein tracking and general meal awareness rather than precise calorie or macro counting. Users who want detailed nutritional tracking alongside their fasting will benefit from pairing Zero with a dedicated calorie or macro tracker such as Lose It! or MacroFactor.
Good to Knows: ⮛ (click to open)
• Zero’s free trial converts automatically to a paid annual subscription on the trial end date — users should set a calendar reminder before the trial begins if they want to evaluate the app without committing to the full year.
• The fasting timer can be started and stopped directly from an Apple Watch, which many users cite as one of the most practically useful features for meal transitions without needing to find and unlock a phone.
• Zero’s Fasting Zones are educational milestones based on general research averages, not personalised measurements — the timing of physiological transitions like ketosis onset varies significantly between individuals based on diet, activity, and metabolic state.
Takeaways: ⮛ (click to open)
• Zero is the most polished and widely used intermittent fasting app available, combining a frictionless timer with the strongest educational content library in the fasting category.
• The free version is genuinely usable for consistent daily fasting, making it a low-risk starting point for anyone new to intermittent fasting who is not ready to commit to a paid subscription.
• Zero Plus at $69.99 per year is worthwhile for users who actively engage with the Fasting Zones, content library, and challenges — but casual users who just need a timer will find the free plan sufficient.
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