ReckonBoxCalculators that show the math.
Precise readings, the formula behind every result, and no account to create. Built to work on any device.
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Popular tools
BMI Calculator
Find your body mass index, weight category, and healthy weight range for your height, using either the WHO or the Asian BMI cutoffs.
BMR Calculator
Find your basal metabolic rate from three formulas at once: Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle.
TDEE Calculator
Find your total daily energy expenditure from your activity level, and the daily calories to lose, maintain, or gain weight.
Body Fat Calculator
Estimate body fat with the US Navy tape method, with the real error margin behind the 3 to 4 percent everyone quotes, plus fat mass, lean mass and FFMI.
Macro Calculator
Turn your calories into daily protein, carbs, and fat, with presets for balanced, low-carb, high-protein, and keto.
Calorie Calculator
Daily calories to lose, maintain or gain, with three BMR formulas and the number nobody prints: what picking the wrong activity level costs you.