Intermittent Fasting Calculator
Plan your intermittent fasting schedule. Choose 16:8, 18:6, 20:4, or OMAD protocol, set your start time, and see your eating and fasting windows.
Select protocol and time, then click Calculate.
How Does the Formula Work?
The Intermittent Fasting Calculator helps you plan your daily fasting and eating windows based on five popular protocols. Enter the time of your last meal and select a fasting protocol. The calculator instantly shows when your fasting period ends and your eating window opens, with a visual color-coded timeline showing the fasting (red) and eating (green) portions of your day.
14:10 = 14h fast + 10h eat (Beginner)
16:8 = 16h fast + 8h eat (Most Popular)
18:6 = 18h fast + 6h eat (Intermediate)
20:4 = 20h fast + 4h eat (Warrior Diet)
23:1 = 23h fast + 1h eat (OMAD)
Fast Ends = Last Meal Time + Fasting Hours
Eating Window = Fast End to Fast End + Eating Hours
Understanding the Protocols
The 16:8 method is the most popular and well-researched protocol. You skip breakfast and eat between roughly noon and 8 PM. Since 7-8 hours of the fasting window occur during sleep, you are only consciously fasting for about 8 hours. The 18:6 protocol narrows the eating window further, often used by people who have adapted to 16:8 and want more fasting benefits. The 20:4 (Warrior Diet) allows only a 4-hour eating window, typically in the evening. OMAD (23:1) is the most extreme daily protocol where all calories are consumed in a single meal.
How to Start
Begin with the 14:10 protocol by finishing dinner by 8 PM and eating breakfast at 10 AM. After one to two weeks, gradually extend to 16:8 by pushing breakfast to noon. Stay hydrated during fasting with water, black coffee, or herbal tea. When your eating window opens, focus on nutrient-dense whole foods rather than compensating with junk food. The quality of what you eat matters as much as when you eat.
Common Mistakes
The most common mistake is overeating during the eating window, which negates the caloric benefits of fasting. Another mistake is jumping directly to aggressive protocols like 20:4 or OMAD without building up tolerance. Dehydration is also frequent because many people forget to drink water when they are not eating. Finally, ignoring how your body feels in pursuit of a strict schedule can lead to fatigue, irritability, and disordered eating patterns.
Tips & Recommendations
14:10 beginner to 23:1 OMAD. Progressive difficulty for any experience level.
Color-coded bar shows fasting (red) and eating (green) portions of your day.
See when to stop eating, when fasting ends, and when your eating window closes.
Set any last meal time. Schedule adjusts automatically for your lifestyle.
Frequently Asked Questions
What is intermittent fasting?
Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. It does not specify which foods to eat, but rather when you should eat. The most popular method is 16:8, where you fast for 16 hours and eat within an 8-hour window.
What does 16:8 mean?
16:8 means you fast for 16 hours and have an 8-hour eating window. For example, if your last meal is at 8:00 PM, you can eat again at 12:00 PM the next day.
Which protocol is best for beginners?
The 14:10 protocol is ideal for beginners. You fast for 14 hours (including sleep) and eat within a 10-hour window. Most people already fast 10-12 hours overnight, so 14:10 requires only a small adjustment.
Can I drink water during fasting?
Yes. Water, black coffee, and unsweetened tea are allowed during the fasting window. These contain no calories and do not break the fast. Avoid any drinks with sugar, cream, or artificial sweeteners.
What is OMAD?
OMAD stands for One Meal A Day (23:1 protocol). You eat all your daily calories in a single one-hour window and fast for the remaining 23 hours. This is the most extreme common IF protocol.
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