This calculator estimates how much energy your body uses each day in two steps. First, it calculates your Resting Metabolic Rate (RMR), which is the number of calories your body burns at complete rest to keep vital organs functioning. By default, the tool applies the Mifflin-St Jeor equation, published in 1990: for men, RMR equals (10 multiplied by weight in kilograms) plus (6.25 multiplied by height in centimeters) minus (5 multiplied by age in years) plus 5; for women, the constant at the end is minus 161. If you enter an optional body fat percentage, the calculator switches to the Katch-McArdle formula, which estimates resting energy needs from lean body mass: 370 plus (21.6 multiplied by lean mass in kilograms). Second, your resting value is multiplied by a standard physical activity factor ranging from 1.2 for mostly seated routines to 1.9 for heavy daily training to produce a Total Daily Energy Expenditure (TDEE) estimate.
Once maintenance calories are estimated, the tool adjusts the daily target up or down according to your chosen goal and divides calories across protein (4 calories per gram), carbohydrates (4 calories per gram), and fats (9 calories per gram). While predictive equations are helpful starting points, they have important limits. Two people of the exact same age, height, and weight can have resting metabolic rates that differ by several hundred calories per day due to muscle mass, thyroid function, genetics, sleep quality, and past dieting history. Activity multipliers are also rough averages and can easily overestimate energy burned during workouts.
This calculator is not suitable for children, teenagers who are still growing, pregnant or breastfeeding women, individuals recovering from surgery or illness, or anyone with a history of eating disorders. People taking weight-loss medications or managing chronic health conditions should obtain individualized targets from their medical team rather than relying on an online formula.
Reference sources: Mifflin-St Jeor 1990 paper; Academy of Nutrition and Dietetics; National Institutes of Health (NIH); Mayo Clinic; World Health Organization (WHO).
The Smoothie Builder estimates the nutritional content of a single blended drink by summing standard reference values for four core ingredient categories: a 240-milliliter (8-ounce) liquid base, one standard serving of a protein source, one portion of fruit or greens, and one functional add-in such as seeds, nut powder, or oil. Total calories, grams of protein, total carbohydrates, dietary fiber, and total fats are added together from typical food-label averages. Net carbohydrates are estimated by subtracting dietary fiber from total carbohydrates, and the tool flags whether the net carbohydrate total is relatively low or moderate for a single snack or meal replacement.
This additive method is convenient for comparing recipes before you blend, but it has real-world limits. Actual nutrition values vary significantly by brand, scoop size, fruit ripeness, and how generously you measure ingredients at home. A heaping tablespoon of chia seeds or peanut butter powder can add 40 to 80 extra calories compared with a level scoop. In addition, subtracting all fiber from total carbohydrates is only a rough convention; soluble fibers and sugar alcohols still contribute some absorbable energy and can affect blood glucose differently from person to person. Blending whole fruit also speeds up digestion compared with chewing solid fruit, even when total fiber grams remain the same.
This tool is not suitable for managing food allergies, celiac disease, phenylketonuria, renal potassium or phosphorus restrictions, or strict medical carbohydrate counting for insulin dosing. People with diabetes, kidney disease, digestive disorders, or post-surgical dietary stages should always read the exact nutrition facts panel and ingredient list printed on their own food packages, weigh portions with a digital kitchen scale when precision matters, and consult a registered dietitian or physician before using homemade shakes or smoothies as regular meal replacements.
Reference sources: Academy of Nutrition and Dietetics; National Institutes of Health (NIH); Mayo Clinic; World Health Organization (WHO); Mifflin-St Jeor 1990 paper.
This tool calculates three simple body-size screening numbers from your weight, height, and waist measurement. First, Body Mass Index (BMI) is calculated by dividing your weight in kilograms by the square of your height in meters (kg/m²). For general adult populations, standard categories place a BMI below 18.5 as underweight, 18.5 to 24.9 as the standard reference range, 25.0 to 29.9 as overweight, and 30.0 or higher as obesity. Second, the Healthy Weight Window shows the weight span that corresponds to a BMI between 18.5 and 24.9 for your exact height. Third, Waist-to-Height Ratio (WHtR) is calculated by dividing your waist circumference in centimeters by your height in centimeters. Public health guidelines often use a ratio below 0.50—keeping your waist circumference under half your height—as a general indicator of lower central fat accumulation.
Although BMI and WHtR are widely used because they require only a scale and a tape measure, both formulas have major limitations. BMI measures total weight relative to height, not body composition. It cannot distinguish between fat mass, skeletal muscle, bone density, or fluid retention. As a result, strength athletes and muscular individuals frequently register in the overweight category despite having low body fat, while older adults with low muscle mass can have a normal BMI alongside elevated abdominal fat. Standard BMI cutoffs also do not account for ethnic and sex differences in fat distribution, and waist measurements can vary depending on posture, recent meals, and where the tape is placed around the abdomen.
This calculator is not suitable for children or adolescents (who require age- and sex-specific growth percentiles), pregnant women, competitive bodybuilders, amputees, or frail older adults. Neither BMI nor WHtR can diagnose any health condition on its own; they are simple anthropometric screening ratios best interpreted alongside blood pressure, blood lipid panels, blood glucose testing, physical activity habits, and a full evaluation by a qualified healthcare professional.
Reference sources: World Health Organization (WHO); National Institutes of Health (NIH); Mayo Clinic; Academy of Nutrition and Dietetics; Mifflin-St Jeor 1990 paper.
This hydration calculator estimates total daily water and dietary electrolyte targets using body weight, exercise duration, and general eating style. Baseline fluid intake starts at 35 milliliters per kilogram of body weight per day, a common adult rule of thumb, and adds 350 milliliters for every 30 minutes of moderate sweating or physical activity. For sodium, the calculator applies a strict upper cap of 2,300 milligrams per day for standard and low-carbohydrate options, aligning with general public health upper limits for adults. Only when the Hot Climate or Endurance Training option is selected does the sodium estimate allow up to a maximum of 3,500 milligrams per day to account for heavy sweat losses. Potassium and magnesium estimates reflect general adult dietary intakes from whole foods, while the caffeine ceiling is capped at 4 milligrams per kilogram of body weight up to a maximum of 400 milligrams per day.
These formulas provide broad ballpark figures and have clear limitations. Total water needs include moisture from food (which typically supplies about one-fifth of daily fluid) as well as plain water, tea, and other beverages. Individual sweat rates vary widely from under 0.5 liters to more than 2 liters per hour depending on humidity, clothing, fitness level, and heat acclimatization, and sweat sodium concentration differs substantially between individuals.
This calculator is not suitable for anyone with chronic kidney disease, congestive heart failure, high blood pressure, adrenal disorders, or cirrhosis, nor for people taking diuretics, ACE inhibitors, angiotensin receptor blockers, lithium, or potassium-sparing medications. Pregnant or breastfeeding women, children, older adults, and endurance athletes training for multi-hour events in extreme heat should seek personalized hydration and electrolyte guidance from a physician or sports dietitian rather than relying on general online estimates, and should monitor practical hydration signs such as thirst and pale-straw urine color.
Reference sources: World Health Organization (WHO); National Institutes of Health (NIH); Mayo Clinic; Academy of Nutrition and Dietetics; Mifflin-St Jeor 1990 paper.
This planner uses simple 24-hour clock arithmetic to map out a time-restricted eating schedule based on when you finish your final meal or calorie-containing drink of the evening. When you select a schedule such as 14:10, 16:8, 18:6, or 20:4, the first number represents consecutive hours without calorie intake (water and unsweetened beverages only), and the second number represents the remaining hours of the day available for meals and snacks. The calculator adds your chosen fasting duration to your evening meal hour to display your next-day first meal time, and also marks the 12-hour overnight point when stored liver glycogen typically begins to decline after an evening meal.
While a structured clock window helps some adults reduce late-night snacking, the timer has important physiological limits. A clock cannot measure your actual blood glucose, insulin levels, ketone production, or cellular processes, all of which depend heavily on how many calories and carbohydrates you ate at dinner, your muscle glycogen stores, and your physical activity level. Furthermore, compressing meals into a short eating window does not automatically produce weight loss if total calorie intake exceeds your daily energy expenditure, and very narrow eating windows can make it harder to meet daily protein, fiber, and micronutrient targets comfortably.
Time-restricted eating is not suitable for children or teenagers, pregnant or breastfeeding women, individuals who are underweight, or anyone with a personal history of anorexia, bulimia, or binge-eating disorder. People with type 1 or type 2 diabetes—especially those taking insulin, sulfonylureas, or other glucose-lowering medications—face a serious risk of hypoglycemia (dangerously low blood sugar) during prolonged fasting windows, and individuals with gastroesophageal reflux, low blood pressure, or daily medication schedules that require food should never fast without direct medical supervision from their physician.
Reference sources: Mayo Clinic; National Institutes of Health (NIH); Academy of Nutrition and Dietetics; World Health Organization (WHO); Mifflin-St Jeor 1990 paper.