Pick an IF protocol and your first meal time. Get the exact eating and fasting window, plus how many calories to eat per eating hour.
IF protocols split each day into a fasting window and an eating window. 16:8 is the most popular (research-backed for weight loss and insulin sensitivity). Here's the full comparison:
| Protocol | Fasting | Eating | Best for |
|---|---|---|---|
| 16:8 (Leangains) | 16 h | 8 h | Beginners, weight loss, insulin sensitivity |
| 18:6 | 18 h | 6 h | Intermediate, autophagy |
| 20:4 (Warrior) | 20 h | 4 h | Advanced, deep ketosis |
| OMAD | 23 h | 1 h | Experienced, time-restricted eating |
Source: Tinsley GM & La Bounty PM (2015). Effects of intermittent fasting on body composition and clinical health markers. Nutr Rev 73(10):661-674. Water, black coffee, and plain tea do not break the fast.
Also known as: IF calculator, time-restricted eating calculator, 16:8 calculator, 18:6 fasting calculator, 20:4 warrior diet calculator, OMAD calculator, eating window calculator, fasting hours calculator, Leangains calculator. All return the same eating and fasting schedule.
Cross-checked against authoritative formulas (IRS, NIST, ACSM) and updated for 2025/2026 tax years and rates.
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FAQ
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Intermittent fasting (IF) is an eating pattern that cycles between fasting and eating windows. It does not specify what to eat — only when. The most popular protocol is 16:8 (fast 16 hours, eat within 8 hours). Other protocols: 18:6, 20:4 (Warrior diet), OMAD (one meal a day), and 5:2 (eat normally 5 days, restrict to 500-600 kcal on 2 non-consecutive days). IF works primarily by reducing the eating window, which often reduces total calorie intake without explicit counting. Our intermittent fasting calculator schedules any of these protocols.
How it works
Our intermittent fasting calculator returns your eating and fasting schedule for any IF protocol (16:8, 18:6, 20:4, OMAD) plus calories per eating hour.
Choose 16:8 (most popular, research-backed), 18:6, 20:4 (Warrior diet), or OMAD (one meal a day). Each splits the day into a fasting window and an eating window.
Type the time of day you'd like to break your fast. The intermittent fasting calculator computes when your eating window closes and when the next fast begins.
Optionally enter your TDEE so the calculator can show calories per eating hour — useful for hitting your daily calorie goal across fewer meals.
The intermittent fasting calculator shows the eating window, fasting window, and (if you entered TDEE) how many calories to eat per eating hour. Water, black coffee, and plain tea do not break the fast. The share button creates a link with your inputs pre-filled.
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