7-day fast
7 Day Fast Weight Loss Calculator
A seven-day water fast produces a larger cumulative calorie deficit than shorter fasts.
The 7-day preset is pre-selected. Week-long fasts require medical clearance for many people.
Largest deficit
Seven days of TDEE burn adds up.
Water taper
Glycogen water is mostly gone by day 3; later loss skews toward fat.
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.