Intermittent Fasting Calculator
Plan your intermittent fasting schedule. Choose a protocol (16:8, 18:6, 20:4, OMAD, or 5:2), set your eating window start time, and get your exact fasting and eating times for the day.
Eating Window
12:00 PM
to
8:00 PM
8 hours to eat
Fasting Window
8:00 PM
to
12:00 PM
16 hours fasting
Tips for 16:8 (Most popular)
- -Black coffee and tea are fine during the fast - they don't break it.
- -Most people skip breakfast and eat from noon to 8pm.
- -Stay hydrated - aim for 2-3L of water during the fast window.
About the Intermittent Fasting Calculator
The Intermittent Fasting Calculator on ToolHaven is a free, browser-based tool that helps you plan your intermittent fasting schedule. Choose a protocol (16:8, 18:6, 20:4, OMAD, or 5:2), set your eating window start time, and get your exact fasting and eating times for the day. It runs entirely in your browser, so no data is sent to any server, and no account or signup is required. Whether you are a student, professional, or just someone looking for a quick answer, this tool gives you accurate results in seconds.
How to use the Intermittent Fasting Calculator
Using this tool is straightforward. Pick the fasting protocol that suits your lifestyle. Set what time you want to start eating (your eating window open time). The calculator shows exactly when your eating window closes and when your next fast begins. Read the protocol-specific tips below to set yourself up for success.
Results are updated instantly as you enter values, so there is no need to click a submit button. You can adjust inputs freely and compare different scenarios in real time.
Why use ToolHaven?
ToolHaven offers 178+ free online calculators and tools across categories including Finance, Health, Math, Education, and more. All tools are free to use, require no installation, and work on any device. Your inputs never leave your browser, so your data stays private. The Intermittent Fasting Calculator is part of our Health collection. Explore related tools in the sidebar to get more done in one place.
How to use
- Pick the fasting protocol that suits your lifestyle.
- Set what time you want to start eating (your eating window open time).
- The calculator shows exactly when your eating window closes and when your next fast begins.
- Read the protocol-specific tips below to set yourself up for success.
Related tools:
Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. Unlike a diet, it doesn't tell you what to eat - it tells you when. The most popular protocol is 16:8, where you fast for 16 hours and eat within an 8-hour window. Most people skip breakfast and eat from around noon to 8pm.
The reason IF works for weight management is simple: restricting your eating window naturally leads to fewer calories consumed. There's also research suggesting benefits to insulin sensitivity, cellular repair (autophagy), and metabolic health - though much of the research is still ongoing. Pick a protocol that fits your lifestyle; the best one is the one you'll actually stick to.
Frequently Asked Questions
Does coffee or tea break the fast?
Black coffee and plain tea (no milk, sugar, or cream) don't break the fast. They have negligible calories and may actually enhance some fasting benefits. Bulletproof coffee (with butter or MCT oil) technically breaks the fast due to the calories.
Can I exercise while fasting?
Yes. Many people train in a fasted state without issues. Some find performance slightly affected, especially for high-intensity or heavy lifting. If you feel lightheaded or your performance suffers badly, try training near the end of your fasting window when you're closer to eating.
What can I eat during the eating window?
IF doesn't prescribe specific foods. However, eating mostly whole foods - protein, vegetables, healthy fats, and complex carbs - will give much better results than eating whatever you want in the window. The eating window is not a license to binge.
Is 16:8 suitable for everyone?
Not always. People who are pregnant, breastfeeding, have a history of eating disorders, are underweight, or have certain medical conditions should avoid IF or consult a doctor first. Teenagers and children shouldn't do extended fasting protocols.