Reviewed by Dr. David Chen, CNS — Health & Nutrition Specialist
Planning a water fast? Use our professional water fast calculator to estimate your potential weight loss, hydration requirements, and daily caloric deficit during your fasting period.
Water Fast Calculator
Estimated Results
Please enter your data and click Calculate.
Water Fast Calculator Formula:
Weight Loss (lbs) = (TDEE × Duration) / 3,500
Water Intake (oz) = Weight × 0.67 + (Activity Bonus)
Formula Source: Healthline Nutrition Guide, Mayo Clinic Hydration Research
Variables:
- Current Weight: Your total body mass used to calculate BMR.
- Fast Duration: The total number of consecutive days of fasting.
- Activity Level: Your TDEE multiplier based on daily movement.
- Age: Factor used in the Mifflin-St Jeor equation for basal metabolism.
Related Calculators:
- Intermittent Fasting Schedule Creator
- Daily Electrolyte Requirement Tool
- Body Fat Percentage Estimator
- Autophagy Timeline Calculator
What is Water Fast Calculator?
A water fast calculator is a specialized health tool designed to help individuals estimate the physiological changes that occur during a total fast where only water is consumed. By integrating your personal metrics like weight and age, it predicts how much fat mass your body might metabolize for energy.
This tool is essential for safety, as it also calculates the minimum recommended water intake to prevent dehydration and electrolyte imbalances, which are common risks during extended fasting periods.
How to Calculate Water Fasting Weight Loss (Example):
- Determine your BMR (e.g., 1,800 kcal).
- Multiply BMR by Activity Level (1.2) = 2,160 TDEE.
- Multiply TDEE by Days (3) = 6,480 total caloric deficit.
- Divide deficit by 3,500 (calories in 1lb of fat) = ~1.85 lbs lost.
Frequently Asked Questions (FAQ):
Is a water fast safe for everyone? No, pregnant women, children, and people with eating disorders or type 1 diabetes should avoid water fasting without medical supervision.
How much weight will I lose on a 3-day water fast? Typically, users lose 1.5 to 3 lbs of fat mass, though initial scale weight might drop more due to water loss.
Can I exercise during a water fast? Light movement is usually fine, but intense cardio is not recommended as your body has no immediate glycogen stores.
Do I need electrolytes? Yes, for any fast longer than 24 hours, supplementing sodium, magnesium, and potassium is crucial to prevent dizziness.