Water Fasting Calculator
Estimate your fasting end time, resting energy needs, theoretical energy deficit, and a general daily fluid range. This tool is for planning and education—not medical advice.
Enter fasting details
Result
Enter your planned start time and details to estimate your fasting window.
Plan conservatively
Longer is not automatically better. A shorter, supervised fasting plan is safer than extending a fast because the calculator shows a number.
Hydration is individual
Climate, activity, medicines, and health conditions affect fluid needs. Excessive water can also be dangerous, especially without electrolytes.
Scale loss is not fat loss
Early weight changes during fasting are often influenced by water and glycogen. Theoretical energy deficit is not a prediction of actual fat loss.
Frequently asked questions
What does this water fasting calculator estimate?
It calculates the planned end time, estimates resting energy needs with the Mifflin–St Jeor equation, scales energy use for the fasting period, and gives a broad fluid range based on body weight.
Does the calorie estimate equal expected weight loss?
No. The energy figure is only a mathematical estimate. Actual scale change includes water, glycogen, food in the digestive tract, and other factors.
Is a 48- or 72-hour water fast safe?
Extended fasting can cause dehydration, electrolyte problems, low blood pressure, low blood sugar, and medication complications. It should not be started without qualified medical guidance.
Can I drink unlimited water while fasting?
No. Drinking excessive water can dilute sodium levels. Drink according to thirst and medical advice, particularly during longer fasts or in hot weather.
Results are estimates generated locally in your browser from standard formulas and general population data. They are for informational purposes only and do not constitute medical advice. Always consult a qualified healthcare or fitness professional before making changes to your training, diet or health plan. VisionVix accepts no liability for decisions made based on this tool's output.
