4-day fast
4 Day Water Fast Calculator
A four-day fast sits between a short 3-day reset and a longer 5-day extended fast.
Duration is pre-set to 4 days—adjust your stats and click Calculate.
After the water flush
Day 4 contributes mostly additional fat loss.
Compare plans
See our 3-day or 5-day calculators to compare durations.
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.