Fasting Weight Loss Calculator
Estimate projected weight change from an intermittent-fasting calorie pattern using adaptive energy-balance math.
Faster but often manageable with adequate protein and recovery.
Activity selection: Lightly Active. Light exercise 1-3 days/week.
Projected Weekly Loss Pace
Interpretation is based on projected percent body-weight change per week in your fasting setup.
| RANGE | CATEGORY |
|---|---|
| -1-0 | Weight Gain Average energy intake appears above expenditure in this setup. |
| 0-0.25 | Very Slow Low weekly rate. Useful for maintenance-adjacent phases or conservative starts. |
| 0.25-0.75 | Steady Typical sustainable pace for many adults. |
| 0.75-1 | Brisk Faster but often manageable with adequate protein and recovery. |
| 1-1.50 | Aggressive Aggressive pace. Monitor performance, hunger, and sleep quality closely. |
| 1.50-2 | Very Aggressive High weekly rate with increased lean-mass retention risk. |
| 2+ | Extreme Very high projected pace. Medical supervision is recommended. |
How This Fasting Calculator Works
The model estimates daily energy expenditure from Mifflin-St Jeor BMR and activity level, then simulates day-by-day weight change across fasting and non-fasting intake days.
Unlike a single static deficit formula, this projection recalculates expenditure as body weight changes, which reduces overestimation over longer timelines.
Practical Use
Use this as a planning tool, not a guarantee. Real outcomes are influenced by adherence, spontaneous intake changes, sleep, stress, medications, and fluid shifts.
For non-fasting calorie setup, estimate maintenance with the TDEE Calculator and set a target with the Calorie Deficit Calculator. For meal-level intake estimates from food photos, use the Calorie Estimator. For step-based walking output, add the Steps to Calories Calculator.
If you want a quick protocol comparison (16:8, 18:6, OMAD, or 5:2), use the Intermittent Fasting Calculator.
If you prefer a non-fasting setup based on one daily calorie target, use the standard daily-intake timeline model.
To summarize progress after a phase, calculate net percentage change with the start-to-current percentage tracker.
References
- NIDDK overview of adult overweight and obesity management:NIDDK Adult Overweight and Obesity
- Mifflin-St Jeor resting metabolic rate equation (PubMed):A New Predictive Equation for Resting Energy Expenditure
- Time-restricted eating trial in adults with overweight/obesity (JAMA Internal Medicine):Effect of Time-Restricted Eating on Weight Loss
More Tools →
Intermittent Fasting Calculator
Estimate fasting-protocol calorie intake, daily expenditure, and weekly pace.
TDEE Calculator
Estimate total daily energy expenditure from BMR equation and activity level.
Calorie Deficit Calculator
Calculate deficit targets and daily calories from your selected weekly pace.
Calorie Estimator
Estimate meal calories from a photo with AI and confidence ranges.