Intermittent Fasting Calculator
Plan your intermittent fasting schedule with this calculator. Choose your protocol (16:8, 18:6, 20:4, or OMAD), set your first meal time, and get a complete daily schedule showing your eating window, fasting window, and suggested meal times.
Enter Your Details
When you want to eat your first meal
How It Works
Intermittent fasting restricts eating to a set window each day. The 16:8 protocol means 16 hours of fasting and an 8-hour eating window — the most popular and sustainable option. The 18:6, 20:4, and OMAD (One Meal a Day, approximately 23:1) protocols progressively narrow the eating window. This calculator takes your preferred first meal time and calculates your entire daily schedule, including when to stop eating and when your fasting window begins and ends.
Quick Reference
| Protocol | Fasting Window | Eating Window | Typical Meals | Difficulty |
|---|---|---|---|---|
| 12:12 | 12 hours | 12 hours | 3 meals + snacks | Beginner |
| 14:10 | 14 hours | 10 hours | 3 meals | Easy |
| 16:8 | 16 hours | 8 hours | 2-3 meals | Moderate |
| 18:6 | 18 hours | 6 hours | 2 meals | Challenging |
| 20:4 | 20 hours | 4 hours | 1-2 meals | Advanced |
| OMAD (23:1) | 23 hours | 1 hour | 1 large meal | Very Advanced |
| 5:2 (weekly) | 2 full days | 5 normal days | Normal on eat days | Moderate |
| ADF | Every other day | Every other day | Normal on eat days | Advanced |
The 16:8 protocol is the most studied and sustainable for most people. Start here before trying more restrictive protocols.
Frequently Asked Questions
- Which intermittent fasting protocol is best for weight loss?
- The 16:8 protocol is the most studied and sustainable for long-term weight loss. It naturally reduces calorie intake by about 300-500 calories per day. More restrictive protocols (18:6, 20:4) may produce faster initial results but are harder to maintain.
- Can I drink water during the fasting window?
- Yes. Water, black coffee, and plain tea are allowed during fasting and will not break your fast. Avoid anything with calories, including milk, sugar, or flavoured drinks. Staying hydrated during fasting is important.
- Is intermittent fasting safe for everyone?
- IF is not recommended for pregnant or breastfeeding women, children, people with eating disorders, or those with type 1 diabetes. If you have any medical condition or take medication, consult your GP before starting. Most healthy adults can safely try 16:8.
- How long before I see results with intermittent fasting?
- Most people notice reduced bloating within the first week. Measurable weight loss typically begins in weeks 2-4, with 0.5-1 kg per week being typical when combined with a balanced diet. Metabolic benefits like improved insulin sensitivity can develop within 2-4 weeks.
How This Is Calculated
- first meal time
- = when you eat your first meal of the day
- eating hours
- = hours in your eating window (8 for 16:8, 6 for 18:6, etc.)
- fasting window
- = hours you abstain from caloric intake
During the fasting window, water, black coffee, and plain tea are permitted. Any caloric intake breaks the fast.
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Disclaimer
This calculator provides estimates for informational purposes only and should not be considered medical advice. Individual results may vary based on factors not captured by these formulas. Consult a healthcare professional before making changes to your diet or exercise routine, especially if you have any existing health conditions.