BMR uses the Mifflin-St Jeor equation from entered age, sex, height, and weight.
Estimated TDEE = BMR × selected activity factor.
Fasting deficit = TDEE × fasting days - calories consumed.
Fat-equivalent change is estimated as deficit ÷ 3,500 calories per pound.
Short-term scale weight can differ due to water, glycogen, sodium, and digestion changes.
Important: This tool does not recommend fasting. Extended fasting can be risky, especially with diabetes, pregnancy, eating disorders, kidney disease, heart disease, or medications. Speak with a healthcare professional.
Result options
Print, copy, or download your result
Use these quick actions after calculating. PDF summary buttons inside the result box still work where available.
Water Fasting Calculator guide
Formula, example, FAQs, and notes
Formula explanation in simple language
Water Fasting Calculator follows the visible calculator rules on this page. In simple terms, it takes the values you enter, applies the main formula steps, then returns a result summary. Key steps: User can select weight in pounds or kilograms. Height is entered as feet and inches for easier use. Weight is converted to kilograms internally before BMR calculation.
User can select weight in pounds or kilograms.
Height is entered as feet and inches for easier use.
Weight is converted to kilograms internally before BMR calculation.
Height feet and inches are converted to total inches, then centimeters.
BMR uses the Mifflin-St Jeor equation from entered age, sex, height, and weight.
Estimated TDEE = BMR × selected activity factor.
Example calculation
Example: enter Sex used for BMR equation: Male, Age: 30, Weight unit: Pounds (lb), Current weight: 180, Height feet: 5. Then press Calculate Result. The calculator uses those inputs to generate a result, interpretation notes, and a downloadable PDF summary.
After changing any input, recalculate and compare the new result with the original assumptions.
Common mistakes and interpretation notes
Do not leave default values unchanged if they do not match your real situation.
Check units carefully before calculating. Mixing inches, feet, pounds, kilograms, days, months, or years can change the result.
Treat the result as an estimate, not a guarantee, quote, diagnosis, settlement promise, or final professional decision.
Do not use lifestyle or medical-adjacent results to start, stop, or change treatment, medication, fasting, or diet plans.
Disclaimer
This tool does not recommend fasting. Extended fasting can be risky, especially with diabetes, pregnancy, eating disorders, kidney disease, heart disease, or medications. Speak with a healthcare professional.
Water Fasting Calculator FAQ
Helpful answers for long-tail searches
How accurate is the Water Fasting Calculator?
The Water Fasting Calculator is accurate to the formula and assumptions shown on the page. Real-world results can change when costs, rates, taxes, laws, health factors, or project conditions differ from the values you enter.
Can I download the Water Fasting Calculator result?
Yes. Use the page result controls to download the PDF summary when available, or use the Print, Copy Result, and Download TXT buttons added below the calculator.
What inputs matter most in the Water Fasting Calculator?
The most important inputs are usually the largest cost, rate, quantity, time, and risk assumptions. Small changes in these fields can move the final result significantly.
Is the Water Fasting Calculator medical advice?
No. This calculator is an educational estimate and is not medical advice. Use it for planning and discussion, then verify important decisions with a qualified professional.
