3-day fast
3 Day Water Fast Calculator
A 3-day water fast is one of the most common extended fast lengths.
The 3-day preset is already selected—enter your details and click Calculate.
Typical range
Many adults see roughly 3–7 lbs on the scale, though results vary widely.
Not all fat
A large share in 72 hours is water; our tool separates both components.
Fill in your details and click Calculate Weight Loss to see your estimated breakdown.
More water fasting calculators
Each tool uses the same science with a preset fast length—or browse our main calculator for all options, guides, and FAQs.
Also see: reference table, trusted resources, FAQ
Medical disclaimer · Estimates only—not medical advice.