Intermittent Fasting Calculator
Plan your intermittent fasting schedule. Pick a protocol and see your eating and fasting windows in one place.
Your fasting window
16 hours fast / 8 hours eat
All plans
| Plan | Fast | Eat |
|---|
How to use the Intermittent Fasting Calculator
Pick a fasting plan from the dropdown and press Calculate Fasting Window. The tool shows your fasting and eating hours, plus a comparison table of all plans. Beginners often start with 12:12 or 14:10 before moving to 16:8.
What is intermittent fasting?
Intermittent fasting is an eating pattern that alternates between fasting and eating. The goal is not just calorie restriction — many people use it to simplify meal timing, improve insulin sensitivity, and support fat loss while preserving muscle.
Popular fasting plans compared
Different plans suit different lifestyles. Use the intermittent fasting calculator to visualize windows:
| Plan | Fast hours | Eat hours | Best for |
|---|---|---|---|
| 12:12 | 12 | 12 | Beginners, maintenance |
| 14:10 | 14 | 10 | Gentle weight loss |
| 16:8 | 16 | 8 | Most popular, steady fat loss |
| 18:6 | 18 | 6 | Fewer, larger meals |
| 20:4 | 20 | 4 | Advanced, one big meal |
| OMAD | 23 | 1 | Advanced, requires careful nutrition |
How to choose a fasting plan
- 12:12: great for beginners and maintenance.
- 16:8: the most popular plan for steady weight loss.
- 18:6 / 20:4: useful if you prefer fewer, larger meals.
- OMAD: advanced and not ideal for everyone; requires careful nutrition planning.
What to eat during eating windows
A shorter eating window does not excuse poor food choices. Prioritize protein using the protein calculator, balance carbs for energy, and keep fats moderate. Use the meal calorie calculator to split your target across one or two meals if you do OMAD.
Focus on whole foods: lean meats, fish, eggs, vegetables, fruits, whole grains, and healthy fats. Avoid binge-eating processed foods just because the fast is over. The macro calculator helps you hit the right ratios within your eating window.
Common myths about fasting
- Myth: Fasting starves your muscles. Fact: Adequate protein (1.6–2.2 g/kg) during eating windows preserves muscle. Use the protein calculator to stay safe.
- Myth: You must eat breakfast. Fact: Meal timing matters less than total nutrition. Skipping breakfast is fine if your eating window fits your schedule.
- Myth: Fasting slows metabolism permanently. Fact: Short-term fasting does not meaningfully change metabolism. Very low-calorie dieting over months can, but typical IF with good nutrition is safe.
- Myth: You can eat anything during eating windows. Fact: Calorie quality matters. Binge-eating junk food still causes weight gain and nutrient deficits.
- Myth: Fasting is a quick fix. Fact: Fasting works best as a sustainable habit combined with consistent nutrition and activity.
Fasting and exercise
Light to moderate exercise is usually fine during fasting. For intense sessions, eating a small meal beforehand can help maintain performance. Use the target heart rate calculator to keep effort in a safe zone. For cardio estimates around your fast, try the walking calorie calculator, cycling calories calculator, or swimming calories calculator.
Fasting and weight loss
Fasting helps many people eat fewer total calories without strict counting. To make it sustainable, pair it with high-protein meals using the protein calculator and a sensible daily calorie target from the calorie calculator.
Related guides
Intermittent Fasting for Beginners
A beginner-friendly guide to intermittent fasting: popular plans, safety tips, what to eat, and how to combine it with calorie and macro targets.
Maintenance Calories: How to Stay at Your Ideal Weight
Pair your fasting schedule with a stable maintenance calorie target for long-term results.
Sources and further reading
These independent, authoritative sources inform the methods used on this page.
Frequently asked questions
What is intermittent fasting?
Intermittent fasting is an eating pattern that cycles between fasting and eating windows. Popular approaches include 16:8, 18:6, and OMAD, and they are used for weight management, simplicity, and metabolic health.
How does the 16:8 method work?
In 16:8 fasting, you fast for 16 hours and eat during an 8-hour window each day. For example, skip breakfast and eat only between 12 pm and 8 pm.
Can I drink coffee while fasting?
Black coffee, plain tea, and water are generally allowed during fasting windows. Adding sugar, milk, or cream can break the fast because it introduces calories.
Is intermittent fasting safe?
For most healthy adults, intermittent fasting is safe, but people with diabetes, eating disorders, or who are pregnant should consult a doctor before starting.
How much weight can I lose with intermittent fasting?
Results vary, but intermittent fasting often produces about 0.5–1 lb (0.2–0.5 kg) of weight loss per week when combined with a modest calorie deficit and good nutrition.
What should I eat during my eating window?
Focus on whole foods, protein, fiber, and healthy fats. Use the <a href='/macro-calculator/'>macro calculator</a> to make sure you hit your protein and calorie targets within your eating window.
Does intermittent fasting slow metabolism?
Short-term fasting does not meaningfully slow metabolism. Long-term very low-calorie dieting can, but typical intermittent fasting paired with adequate nutrition is generally metabolically safe.
Can I exercise while fasting?
Light to moderate exercise is usually fine during fasting. For intense sessions, eating a small meal beforehand can help maintain performance. Use the <a href='/target-heart-rate-calculator/'>target heart rate calculator</a> to keep effort in a safe zone.
Does intermittent fasting cause muscle loss?
Not if you eat enough protein. Aim for 1.6–2.2 g/kg protein during eating windows. Use the <a href='/protein-calculator/'>protein calculator</a> to protect muscle while fasting.
Is 16:8 the best fasting plan?
16:8 is the most popular for steady weight loss, but 12:12 or 14:10 are better for beginners. OMAD is advanced. Use the <a href='/intermittent-fasting-calculator/'>intermittent fasting calculator</a> to compare plans.
Can I do intermittent fasting long term?
Yes. Many people sustain 16:8 or 18:6 for months or years. Long-term success depends on nutrition quality during eating windows and a plan that fits your lifestyle.
Does fasting affect sleep or energy?
Some people feel more energized, while others experience mild fatigue the first 1–2 weeks. Side effects usually pass as your body adapts.