⏰ Intermittent Fasting Calculator
Plan your fasting and eating windows
Written by Albert Mateos · Founder & Editor
Last reviewed: May 2, 2026
How it works
Plan your intermittent fasting schedule with our free calculator. Choose your protocol (16:8, 18:6, 20:4, or OMAD) and get a personalized eating window, fasting schedule, and calorie recommendations. Track when to start and end your fast for optimal results.
How to Use This Calculator
- Select your preferred fasting protocol (16:8, 18:6, 20:4, OMAD).
- Enter your typical wake time and bedtime.
- Choose when you want your eating window to start and end.
- Review the suggested meal timing within your window.
- Plan your calorie and macro targets to fit the condensed schedule.
Example
Inputs: 16:8 protocol, wake 7:00 AM, eating window from 12:00 PM to 8:00 PM.
Result: Two to three meals scheduled at 12:00 PM, 4:00 PM, and 7:30 PM.
What it means: This schedule lets you skip breakfast, eat lunch and dinner normally, and finish the day with enough margin before bedtime for good sleep quality.
Tips
- Start with 14:10 and extend the fast gradually. Jumping straight to 20:4 or OMAD usually causes binge eating and poor adherence.
- Water, black coffee, and plain tea don't break the fast. Anything with calories, protein, or artificial sweeteners may disrupt benefits.
- Fasting doesn't bypass calorie math. If you want fat loss you still need a deficit within your eating window.
- Train during the fed state or break your fast within 1-2 hours post-workout. Training fasted long-term can compromise muscle retention.
- OMAD is hard to hit protein and micronutrient targets. Most people do better with 16:8 or 18:6 long-term.
Disclaimer: This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.
Learn More
Frequently Asked Questions
- Does intermittent fasting slow metabolism?
- Short-term fasting (16-24 hours) does not slow metabolism. Studies show metabolic rate may actually increase slightly during fasts under 48 hours due to norepinephrine release. Prolonged calorie restriction (weeks/months at very low calories) is what causes metabolic adaptation.
- Can I exercise while fasting?
- Yes, but adjust intensity. Light to moderate exercise (walking, Zone 2 cardio) is fine fasted. For intense weightlifting or HIIT, most people perform better in their eating window. If you train fasted, prioritize protein in your first meal after.