Intermittent Fasting & Weight Loss Calculator (16:8, 18:6, OMAD)
Calculate your daily eating window, metabolic ketosis/autophagy milestones, TDEE calorie target, and projected 30-day weight loss.
How to Use the Intermittent Fasting & Weight Loss Calculator (16:8, 18:6, OMAD)
Intermittent fasting (Time-Restricted Eating) structures your day into a defined fasting window and a compressed eating window—most commonly the 16:8 protocol (16 hours of fasting followed by an 8-hour feeding window, such as 12:00 PM to 8:00 PM). After 12 to 16 hours without caloric intake, liver glycogen reserves deplete and circulating insulin drops to baseline, flipping the body’s ‘metabolic switch’ toward lipolysis (fat oxidation).
Formula and Calculation Methodology
- T_last meal: Time of day you finish your final meal and begin fasting
- H_fast: Consecutive fasting hours (14, 16, 18, 20, or 23 hours)
- 3,500 kcal: Approximate metabolizable energy stored in 1 pound of human adipose tissue
While fasting improves insulin sensitivity and naturally curbs late-night snacking, long-term fat loss is ultimately governed by energy balance across your eating window. Combining a 16:8 or 18:6 schedule with a sustainable 15% to 20% caloric deficit (and 0.8g of protein per pound of bodyweight) maximizes adipose tissue loss while preserving lean skeletal muscle.
Physiological Timeline of Fasting Stages by Hour
| Hours Fasted | Metabolic Stage | Insulin & Blood Sugar | Primary Fuel Source |
|---|---|---|---|
| 0 – 4 Hours | Anabolic / Fed State | Elevated insulin & glucose | Dietary glucose |
| 4 – 12 Hours | Post-Absorptive State | Insulin steadily falling | Liver glycogen stores |
| 12 – 16 Hours | Metabolic Switch / Lipolysis | Low baseline insulin | Free fatty acids + glycogen |
| 16 – 20 Hours | Nutritional Ketosis | Peak glucagon & HGH | Fatty acids & ketone bodies |
| 20 – 24+ Hours | Autophagy Activation | Minimal insulin / AMPK high | Ketones & cellular recycling |
Frequently Asked Questions
Does black coffee or unsweetened tea break a fast?
No. Plain water, sparkling mineral water, black coffee, and unsweetened green or herbal teas contain negligible calories (< 5 kcal) and do not trigger an insulin response, keeping you in a fasted state.
What is the best intermittent fasting schedule for beginners?
Starting with a 14:10 window for one week and graduating to the 16:8 protocol (skipping breakfast or eating an early dinner) offers the highest long-term adherence in clinical trials.
Will intermittent fasting cause muscle loss?
Not if you consume adequate daily protein (1.6–2.2 g/kg bodyweight) during your eating window and perform resistance training; fasting naturally elevates Human Growth Hormone (HGH), which helps preserve lean tissue.