Caffeine vs Alcohol Hydration Calculator

About this calculator

Both caffeine and alcohol have a mild diuretic effect, increasing urine output and offsetting some of the fluid you take in from the same drink. This calculator estimates your net fluid balance by subtracting an estimated diuretic fluid loss — a fraction of the caffeine and alcohol volumes consumed, based on research showing the diuretic effect is modest and largely absent in habitual consumers — from your total fluid intake across all beverages.

The old idea that “coffee and beer count against your hydration” is largely outdated — research published in outlets like the British Journal of Nutrition has shown the net fluid contribution of moderate caffeinated drinks is still positive — but athletes, people in hot climates, and anyone monitoring fluid intake for a medical reason still find it useful to see a rough net number rather than assume every ounce of coffee, tea, or beer counts fully toward daily hydration, especially at higher intake levels where the diuretic effect becomes more noticeable.