Intermittent Fasting Calculator
Use this intermittent fasting calculator to choose a fasting schedule and see your eating and fasting windows across the day.
Updated August 3, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Intermittent Fasting Windows Are Calculated
Every other calculator on this site starts from something about your body, your weight, your age, your stats. This one doesn't. Intermittent fasting is a schedule, not a physiology problem, so this tool works from a protocol and a start time alone.
What This Calculator Measures
This is a scheduling tool, not a physiological calculator. Your eating and fasting windows come from the protocol you choose, not from your personal stats.
Step 1: Choose Your Protocol
16:8, 18:6, and 14:10 are daily protocols defined by the number of fasting hours to eating hours. 5:2 and alternate-day fasting instead work on a day-based weekly pattern rather than a daily clock-time window.
Step 2: Set Your Eating Window Start Time
For daily protocols, we take your chosen start time and the protocol's eating-hour count to calculate your exact eating and fasting windows in clock time.
How This Calculator Computes Your Result
Pick a protocol and, for daily protocols, an eating-window start time. We calculate the end of your eating window by adding the protocol's eating-hour count, and everything outside that window becomes your fasting period.
Step 3: Display the Result as a Timeline
Rather than plain text alone, we show your eating and fasting windows as a color-coded 24-hour timeline bar, making your schedule easy to read and share at a glance.
A Note on Accuracy
This is a scheduling tool, not a physiological calculator, your window length is a protocol choice, not something derived from your personal stats. A large randomized trial comparing alternate-day fasting directly against daily calorie restriction found no significant difference in weight loss between the two approaches. Intermittent fasting is not appropriate for everyone: people with a history of disordered eating, pregnant or breastfeeding people, and those with certain medical conditions (such as insulin-dependent diabetes) should consult a doctor before trying it.
Frequently Asked Questions
Does intermittent fasting burn more fat than regular calorie restriction?
Research to date generally shows intermittent fasting produces weight loss comparable to standard calorie restriction at the same calorie deficit, not a distinct metabolic advantage¹, a finding also confirmed directly in a large randomized trial². Its main benefit for many people is that a shorter eating window can make it easier to stick to a calorie target.
Which protocol should I choose?
There's no single best protocol, it depends on what fits your schedule and lifestyle. 16:8 and 14:10 are common starting points with a daily eating window, while 5:2 and alternate-day fasting work on a weekly, day-based pattern instead.
Is intermittent fasting safe for everyone?
No. People with a history of disordered eating, pregnant or breastfeeding people, and those with certain medical conditions (such as insulin-dependent diabetes) should consult a doctor before trying intermittent fasting.
How do 5:2 and alternate-day fasting work differently from 16:8?
16:8, 18:6, and 14:10 are daily eating-window protocols, you eat and fast at the same times every day. 5:2 involves eating normally 5 days a week and significantly restricting calories on 2 non-consecutive days. Alternate-day fasting alternates between normal eating days and fasting or very-low-calorie days.
Sources
Intermittent Fasting Calculator
Use this intermittent fasting calculator to choose a fasting schedule and see your eating and fasting windows across the day.
Updated August 3, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Intermittent Fasting Windows Are Calculated
Every other calculator on this site starts from something about your body, your weight, your age, your stats. This one doesn't. Intermittent fasting is a schedule, not a physiology problem, so this tool works from a protocol and a start time alone.
What This Calculator Measures
This is a scheduling tool, not a physiological calculator. Your eating and fasting windows come from the protocol you choose, not from your personal stats.
Step 1: Choose Your Protocol
16:8, 18:6, and 14:10 are daily protocols defined by the number of fasting hours to eating hours. 5:2 and alternate-day fasting instead work on a day-based weekly pattern rather than a daily clock-time window.
Step 2: Set Your Eating Window Start Time
For daily protocols, we take your chosen start time and the protocol's eating-hour count to calculate your exact eating and fasting windows in clock time.
How This Calculator Computes Your Result
Pick a protocol and, for daily protocols, an eating-window start time. We calculate the end of your eating window by adding the protocol's eating-hour count, and everything outside that window becomes your fasting period.
Step 3: Display the Result as a Timeline
Rather than plain text alone, we show your eating and fasting windows as a color-coded 24-hour timeline bar, making your schedule easy to read and share at a glance.
A Note on Accuracy
This is a scheduling tool, not a physiological calculator, your window length is a protocol choice, not something derived from your personal stats. A large randomized trial comparing alternate-day fasting directly against daily calorie restriction found no significant difference in weight loss between the two approaches. Intermittent fasting is not appropriate for everyone: people with a history of disordered eating, pregnant or breastfeeding people, and those with certain medical conditions (such as insulin-dependent diabetes) should consult a doctor before trying it.
Frequently Asked Questions
Does intermittent fasting burn more fat than regular calorie restriction?
Research to date generally shows intermittent fasting produces weight loss comparable to standard calorie restriction at the same calorie deficit, not a distinct metabolic advantage¹, a finding also confirmed directly in a large randomized trial². Its main benefit for many people is that a shorter eating window can make it easier to stick to a calorie target.
Which protocol should I choose?
There's no single best protocol, it depends on what fits your schedule and lifestyle. 16:8 and 14:10 are common starting points with a daily eating window, while 5:2 and alternate-day fasting work on a weekly, day-based pattern instead.
Is intermittent fasting safe for everyone?
No. People with a history of disordered eating, pregnant or breastfeeding people, and those with certain medical conditions (such as insulin-dependent diabetes) should consult a doctor before trying intermittent fasting.
How do 5:2 and alternate-day fasting work differently from 16:8?
16:8, 18:6, and 14:10 are daily eating-window protocols, you eat and fast at the same times every day. 5:2 involves eating normally 5 days a week and significantly restricting calories on 2 non-consecutive days. Alternate-day fasting alternates between normal eating days and fasting or very-low-calorie days.
Sources
Intermittent Fasting Calculator
Use this intermittent fasting calculator to choose a fasting schedule and see your eating and fasting windows across the day.
Updated August 3, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Intermittent Fasting Windows Are Calculated
Every other calculator on this site starts from something about your body, your weight, your age, your stats. This one doesn't. Intermittent fasting is a schedule, not a physiology problem, so this tool works from a protocol and a start time alone.
What This Calculator Measures
This is a scheduling tool, not a physiological calculator. Your eating and fasting windows come from the protocol you choose, not from your personal stats.
Step 1: Choose Your Protocol
16:8, 18:6, and 14:10 are daily protocols defined by the number of fasting hours to eating hours. 5:2 and alternate-day fasting instead work on a day-based weekly pattern rather than a daily clock-time window.
Step 2: Set Your Eating Window Start Time
For daily protocols, we take your chosen start time and the protocol's eating-hour count to calculate your exact eating and fasting windows in clock time.
How This Calculator Computes Your Result
Pick a protocol and, for daily protocols, an eating-window start time. We calculate the end of your eating window by adding the protocol's eating-hour count, and everything outside that window becomes your fasting period.
Step 3: Display the Result as a Timeline
Rather than plain text alone, we show your eating and fasting windows as a color-coded 24-hour timeline bar, making your schedule easy to read and share at a glance.
A Note on Accuracy
This is a scheduling tool, not a physiological calculator, your window length is a protocol choice, not something derived from your personal stats. A large randomized trial comparing alternate-day fasting directly against daily calorie restriction found no significant difference in weight loss between the two approaches. Intermittent fasting is not appropriate for everyone: people with a history of disordered eating, pregnant or breastfeeding people, and those with certain medical conditions (such as insulin-dependent diabetes) should consult a doctor before trying it.
Frequently Asked Questions
Does intermittent fasting burn more fat than regular calorie restriction?
Research to date generally shows intermittent fasting produces weight loss comparable to standard calorie restriction at the same calorie deficit, not a distinct metabolic advantage¹, a finding also confirmed directly in a large randomized trial². Its main benefit for many people is that a shorter eating window can make it easier to stick to a calorie target.
Which protocol should I choose?
There's no single best protocol, it depends on what fits your schedule and lifestyle. 16:8 and 14:10 are common starting points with a daily eating window, while 5:2 and alternate-day fasting work on a weekly, day-based pattern instead.
Is intermittent fasting safe for everyone?
No. People with a history of disordered eating, pregnant or breastfeeding people, and those with certain medical conditions (such as insulin-dependent diabetes) should consult a doctor before trying intermittent fasting.
How do 5:2 and alternate-day fasting work differently from 16:8?
16:8, 18:6, and 14:10 are daily eating-window protocols, you eat and fast at the same times every day. 5:2 involves eating normally 5 days a week and significantly restricting calories on 2 non-consecutive days. Alternate-day fasting alternates between normal eating days and fasting or very-low-calorie days.