Fasting calculator
Not sure which intermittent fasting schedule is right for you? Answer four quick questions and get a personalized recommendation based on your goals, experience, daily routine, and activity level.
What is your primary goal?
This helps us recommend a fasting method aligned with what you want to achieve.
How to choose a fasting schedule
Intermittent fasting is not one-size-fits-all. The method that works for a sedentary office worker focused on longevity is very different from the one that suits a competitive athlete trying to cut weight. The right protocol balances three things: effectiveness for your goal, compatibility with your lifestyle, and long-term sustainability.
The most common mistake people make is choosing the most aggressive fasting method they can find, assuming that more fasting hours equals better results. In practice, the best fasting schedule is the one you can follow consistently for months. A moderate protocol done daily will always outperform an extreme one done sporadically.
Fasting methods explained
12:12 Fasting
The gentlest form of time-restricted eating. You fast for 12 hours and eat within a 12-hour window. This is essentially just avoiding late-night snacking and eating breakfast at a normal time. It is a good starting point for people who have never fasted and want to build the habit before extending their fasting window.
14:10 Fasting
A slightly longer fast that most people can achieve by pushing breakfast back by an hour or two and finishing dinner a bit earlier. The 14-hour fast is long enough to begin depleting liver glycogen and shifting toward fat metabolism. Research shows measurable improvements in blood pressure and insulin sensitivity with 14:10.
16:8 Intermittent Fasting
The most popular and well-studied fasting protocol. Sixteen hours of fasting is long enough to trigger meaningful fat oxidation, autophagy initiation, and growth hormone increases, while the 8-hour eating window is wide enough to consume adequate nutrition across 2-3 meals. This is the default recommendation for most people.
18:6 Fasting
A step beyond 16:8 that adds two more hours of fasting. Those extra hours push you deeper into fat oxidation and ketone production. The narrower 6-hour eating window naturally reduces calorie intake, which makes 18:6 particularly effective for weight loss. Best suited for people with some fasting experience.
20:4 Warrior Diet
An aggressive protocol with a 20-hour fast and a 4-hour eating window. This method maximizes time in ketosis and deep autophagy. The eating window typically consists of one large meal and perhaps a small snack. It requires solid fasting experience and is not recommended for people who exercise intensely, as the narrow window makes adequate nutrition challenging.
OMAD (One Meal a Day)
The most extreme daily fasting protocol. You eat one large meal within roughly a 1-hour window and fast for the remaining 23 hours. OMAD produces the highest levels of ketones and autophagy of any daily fasting method. However, it is very difficult to meet protein and micronutrient needs in a single meal, so it is only recommended for experienced fasters with moderate activity levels.
5:2 Fasting
A different approach: eat normally five days per week and restrict calories to 500-600 on two non-consecutive days. The 5:2 method is a good option for people who dislike daily fasting restrictions. It offers many of the same metabolic benefits as time-restricted eating but with a weekly rather than daily rhythm.
Alternate Day Fasting
Alternating between normal eating days and fasting days (either full fasts or 500-calorie days). This is one of the most effective protocols for weight loss in clinical studies, but it requires significant discipline. The day-on, day-off pattern can be socially challenging and is best suited for experienced fasters.
Tips for choosing and starting your fasting schedule
- Start conservatively. If you are deciding between two methods, choose the easier one. You can always extend your fasting window later. Starting too aggressively leads to burnout and quitting.
- Match your eating window to your social life. If family dinners are important to you, do not choose a schedule that closes your eating window at 4 PM. Sustainability requires a plan that fits your actual life, not just your ideal one.
- Give it at least two weeks. The first 3-5 days of any new fasting protocol can be uncomfortable as hunger hormones recalibrate. Most people feel fully adapted within 7-14 days. Do not judge a method by how the first three days feel.
- Track your fasts. Consistency is the strongest predictor of results. Using a fasting tracker app helps you build streaks, see your progress, and stay accountable.
- Adjust based on results. After 3-4 weeks, evaluate how you feel. If the protocol feels too easy and you want better results, extend the fast by 1-2 hours. If it feels unsustainable, shorten it. The goal is a method you can follow for months.
When to consult a doctor
Intermittent fasting is safe for most healthy adults, but you should consult a healthcare professional before starting if you:
- Have type 1 or type 2 diabetes, especially if you take insulin or sulfonylureas
- Are pregnant or breastfeeding
- Have a history of eating disorders
- Take medications that must be taken with food at specific times
- Are under 18 years old
- Have a BMI below 18.5 (underweight)
For everyone else, intermittent fasting is one of the most accessible and well-researched dietary strategies available. Pick a schedule that fits your life, stay consistent, and give your body time to adapt.
Common questions about choosing a fasting schedule
How do I choose the right fasting schedule?+
The best fasting schedule depends on four main factors: your health goal (weight loss, longevity, mental clarity, or general health), your experience with fasting, your daily routine, and your exercise intensity. Beginners should start with shorter fasts like 12:12 or 14:10 and gradually extend the fasting window as their body adapts. Our calculator above weighs all these factors to give you a personalized recommendation.
Can I switch fasting methods after I start?+
Yes, and it is actually recommended. Many people begin with a gentler protocol like 14:10 and progress to 16:8 or 18:6 as they become comfortable. There is no need to commit to one method forever. If your goals change, your schedule shifts, or you find a protocol too easy or too difficult, adjust accordingly. The best fasting method is the one you can follow consistently.
Is a longer fast always better?+
No. Longer fasts produce deeper autophagy and ketosis, but they are also harder to sustain and can interfere with exercise performance, social eating, and adequate nutrition. A 16:8 fast done consistently every day for a year will produce better results than a 20:4 fast you abandon after two weeks. Sustainability is the most important factor in choosing a fasting protocol.
What if the calculator recommends a method that feels too hard?+
Start one level below the recommendation. If the calculator suggests 18:6, begin with 16:8 for 2-3 weeks and then extend. Your body needs time to adapt to burning fat for fuel, regulating hunger hormones, and maintaining energy during fasted hours. Gradual progression leads to better long-term adherence than jumping into an aggressive protocol.
Does my exercise schedule affect which fasting method I should use?+
Significantly. Intense exercise requires more calories and more flexible meal timing for proper recovery. People who do heavy strength training or high-intensity workouts generally need wider eating windows (16:8 or 14:10) to consume enough protein and carbohydrates. Sedentary individuals can safely use narrower windows like 20:4 or OMAD because their caloric and recovery needs are lower.
Should shift workers fast differently?+
Yes. Shift workers face unique challenges because their sleep-wake cycle and meal timing change regularly. The most important principle is to anchor your fasting window to your sleep period, regardless of the clock time. A 12:12 or 14:10 protocol offers the flexibility needed to adapt to rotating shifts. Avoid very aggressive fasting protocols when your circadian rhythm is already disrupted.
Start your fasting plan today
FastBreak tracks any fasting schedule -- 12:12, 16:8, 18:6, 20:4, or custom. One tap to start, real-time progress through every fasting zone, and smart notifications to keep you on track.
Download Free