How the Water Fast Weight Loss Calculator Works

The calculator estimates potential daily and total weight loss during a water fast by analyzing basal metabolic rate (BMR), activity level, and average fat-burning rate. It provides an estimate only, not a medical recommendation.

Required Inputs

1. Current Weight

Enter your body weight in kilograms or pounds.

2. Height

Used to calculate BMR and expected energy expenditure.

3. Age & Gender

These factors help estimate metabolic rate more accurately.

4. Activity Level

Choose from:

• Sedentary
• Light activity
• Moderate activity
• Active

5. Fasting Duration

Select the number of fasting days (short, medium, or extended fasts).

Calculation Formula

1. Basal Metabolic Rate (BMR)

Calculated using Mifflin–St Jeor equation to estimate calories burned at rest.

2. Total Daily Energy Expenditure (TDEE)

TDEE=BMR×Activity FactorTDEE = BMR \times Activity\ FactorTDEE=BMR×Activity Factor

3. Estimated Fat Loss

During a water fast, most lost weight is from calorie deficit.
Approximation: 1 lb fat≈3500 calories

4. Daily Weight Loss Estimate

Range typically used by calculators:
0.5 – 1.5 kg per day depending on metabolism, deficit, and water reduction.

5. Total Weight Loss Projection

Expected Loss=Daily Loss×Fasting DaysExpected\ Loss = Daily\ Loss \times Fasting\ DaysExpected Loss=Daily Loss×Fasting Days

The calculator returns a safe estimated range rather than a fixed number.

Outputs Provided

1. Estimated Daily Weight Loss

Shows minimum and maximum predicted loss per day.

2. Total Weight Loss for Selected Days

Predicts cumulative weight loss for your chosen fasting duration.

3. Fat Loss vs Water Loss Breakdown

Provides an estimate of:

• Early water loss
• Later fat-burning phase

4. Adjusted Results Based on Activity

Higher activity increases calorie burn, leading to slightly higher loss.

Use Cases

• Planning short-term fasting goals
• Tracking estimated progress during a water fast
• Comparing fasting durations
• Understanding safe ranges of expected loss
• Checking how activity levels affect results

Important Notes

• Results are estimates, not medical or health advice.
• Water fasting can cause rapid initial weight loss mostly due to water reduction.
• Extended fasting may require medical supervision.
• Not recommended for people with medical conditions, low BMI, or metabolic disorders.

Why Use This Calculator?

• Provides realistic daily and total weight loss ranges
• Adjusts results based on age, gender, activity, and metabolism
• Helps set expectations for short and extended fasts
• Useful for comparison and fasting planning