Intermittent Fasting Calculator
Calculate your fasting window, eating schedule and next meal time for 16:8, 18:6, OMAD and other fasting plans.
Intermittent Fasting Calculator
Enter your last meal time and fasting plan to find your exact eating window
Popular Fasting Calculators
Jump straight to the calculator for your chosen fasting schedule
Popular Fasting Schedules
Compare fasting plans and find the one that fits your lifestyle
A gentle entry-level plan. Most of the fast happens overnight while you sleep.
Reduce snacking and improve eating habits with a moderate fasting window.
The most popular IF schedule for weight loss and appetite control.
Extended fasting for deeper fat-burning and improved metabolic health.
The Warrior Diet. One large meal in a 4-hour eating window each day.
One Meal A Day. Maximum metabolic pressure for experienced practitioners.
How the Fasting Calculator Works
- 1
Enter your last meal time
Select the hour and minute when you finished your last meal. This is your fasting start time — the calculator works from there.
- 2
Choose your fasting plan
Pick from 12:12, 14:10, 16:8, 18:6, 20:4 or OMAD based on your goal and experience. Not sure? Start with 16:8.
- 3
Click Calculate
Instantly see your eating window start and end time, total fasting hours, time remaining and current fasting zone.
- 4
Track with the timer
Use the result to plan your next meal. Open the fasting timer to track your fast in real time with zone indicators and progress tracking.
What is an Eating Window?
An eating window is the daily period during which you consume all your calories. In intermittent fasting, you restrict food intake to a fixed window — typically 4, 6, or 8 hours — and fast for the remaining hours of the day.
For example, in the 16:8 method you might eat between 12:00 PM and 8:00 PM (8-hour window) and fast from 8 PM to 12 PM the next day (16-hour fast). The shorter your eating window, the greater the metabolic benefits — but also the greater the challenge.
The calculator above shows your exact eating window based on your last meal time. You can also open the fasting timer to track your fast in real time.
Fasting Zones & Fat Burning
When does fat burning, ketosis and autophagy begin during a fast?
Why People Use Intermittent Fasting
Research-backed reasons millions have adopted intermittent fasting
Weight Loss
Caloric restriction through time-limited eating
Fat Burning
Body shifts to burning stored fat for fuel
Mental Clarity
Ketones improve brain energy efficiency
Insulin Sensitivity
Regular fasting lowers fasting insulin levels and improves insulin response.
Autophagy Support
Triggers cellular repair and longevity processes
Heart Health
Fasting reduces LDL cholesterol, triglycerides and blood pressure markers.
Fasting Calculator FAQs
Common questions about calculating your fasting window
How do I calculate my fasting window?
To calculate your fasting window, note the time of your last meal and add your fasting duration. For example, if you last ate at 8 PM and follow 16:8, your eating window opens at 12 PM the next day. Our calculator does this automatically — enter your last meal time, choose your plan and click Calculate.
What is the best fasting schedule for beginners?
The 12:12 or 14:10 plans are best for beginners. They require fasting mostly overnight, so much of the fast happens while you sleep. Once comfortable, most people progress to the popular 16:8 schedule — the most well-researched intermittent fasting method for weight loss and metabolic health.
How long should beginners fast?
Beginners should start with 12 hours of fasting per day (12:12). This includes sleep time, making it very manageable. After 1–2 weeks, many progress to 14 or 16 hours. Most health benefits of intermittent fasting — including improved insulin sensitivity and fat burning — appear at 14–16 hours.
What is the 16:8 fasting method?
The 16:8 method means fasting for 16 hours and eating within an 8-hour window each day. A typical schedule: eat between 12 PM and 8 PM, then fast until 12 PM the next day. It is the most popular intermittent fasting schedule because it is easy to sustain and well-supported by research on weight loss and metabolic health.
When does fat burning start during a fast?
Fat burning begins approximately 12 hours into a fast, once liver glycogen stores are mostly depleted. The process accelerates between 12–18 hours. Ketone production starts around 18–24 hours of fasting, at which point many people notice improved mental clarity and sustained energy without hunger.
Intermittent Fasting Calculator: How to Calculate Your Eating Window
An intermittent fasting calculator takes your last meal time and fasting duration to determine when your eating window opens and closes. Instead of manually adding hours — including overnight calculations that cross midnight — the calculator handles all the arithmetic instantly.
The most commonly used fasting schedules are 16:8, 18:6 and OMAD. In 16:8, you fast for 16 hours and eat in an 8-hour window. In 18:6, the eating window shrinks to 6 hours for deeper metabolic benefits. OMAD (One Meal A Day) is the strictest approach, with a single 1-hour eating window per day.
16:8 vs 18:6 vs OMAD: Which Fasting Plan is Right for You?
16:8 is best for beginners and those wanting a sustainable long-term practice. It is the most well-researched schedule and produces consistent results for weight management and metabolic health. Most people eat between 12 PM and 8 PM.
18:6 delivers stronger fat-burning results and is suitable once you are comfortable with 16:8. The 6-hour eating window means you have less time to eat, which naturally reduces caloric intake.
OMAD is for experienced practitioners seeking maximum metabolic pressure. It requires careful nutrition planning to meet daily protein and micronutrient needs within a single meal. Use our calculator to find your OMAD eating window, then use the fasting timer to track the full 23 hours.