Hydration needs vary with body size, climate, and activity. This calculator estimates a daily water target using body weight and optional exercise— a practical starting point, not a rigid quota you must hit to the milliliter.
Thirst, urine color, and how you feel are better day-to-day guides than any formula. Medical conditions affecting fluid balance require professional guidance. This tool is for general information only.
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During fasting windows, plain water, black coffee, and unsweetened tea are typical choices. See Can You Drink Coffee While Fasting? for details.