Free Online Calculators
9 free health calculators for body composition, nutrition, pregnancy, sleep optimization, hydration, and pet care. All calculations are private and run in your browser.
Understanding your body's numbers is the foundation of any health and wellness journey. Whether you are setting a weight loss goal, optimizing your nutrition for athletic performance, planning for a pregnancy, or improving your sleep quality, having accurate health metrics helps you make informed decisions. ThisCalc offers 9 free health calculators built on established medical and nutritional formulas, all running privately in your browser.
Start with the basics: our BMI calculator gives you a quick screening based on height and weight, placing you in a WHO-defined category from underweight to obese. For a more nuanced picture, the body fat calculator uses the US Navy circumference method and BMI-based estimation to approximate your fat-to-lean mass ratio. If you want to know what a healthy target looks like for your frame, the ideal weight calculator compares five established medical formulas including Devine, Robinson, Hamwi, and Miller to provide a range rather than a single number.
Effective nutrition starts with knowing how many calories your body needs. The calorie calculator uses the Mifflin-St Jeor equation to estimate your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE) based on your age, sex, height, weight, and activity level. Take it further with the macro calculator, which breaks your calorie target into specific grams of protein, carbohydrates, and fat based on your goal — whether that is fat loss, muscle gain, maintenance, or a specialized diet like keto or high-protein. Staying hydrated is equally important: the water intake calculator factors in your weight, exercise duration, climate, altitude, and pregnancy status to give you a daily target in the units you prefer.
The pregnancy due date calculator supports three input methods: last menstrual period (LMP), IVF transfer date, or conception date. It calculates your estimated due date using Naegele's rule, shows your current gestational age, identifies your trimester, and lists upcoming milestones like the NT scan, anatomy scan, and fetal viability date. For everyone, the sleep cycle calculator uses the well-established 90-minute sleep cycle model to suggest optimal bedtimes or wake times that align with your natural REM cycles, helping you wake up feeling refreshed rather than groggy.
Your pets deserve the same data-driven care. The dog food calculator uses veterinary Resting Energy Requirement (RER) and Maintenance Energy Requirement (MER) formulas to calculate your dog's daily calorie needs based on weight, age, activity level, and weight management goals. It even includes a treat budget so you know how many calories to reserve for training rewards without overfeeding.
These calculators use established formulas from medical literature and nutrition science, but they are screening and planning tools — not diagnostic instruments. Always consult a healthcare professional for medical decisions, dietary changes, or pregnancy care. Your data stays completely private: every calculation runs in your browser with no server processing, no accounts, and no data storage.
BMI (Body Mass Index) is a screening metric that estimates body fat based on height and weight. It is calculated by dividing weight in kilograms by height in meters squared (kg/m2). A BMI of 18.5-24.9 is considered normal weight, 25-29.9 is overweight, and 30+ is obese. While BMI does not directly measure body fat, it correlates with more expensive direct measures and is a useful starting point for health assessments.
Daily calorie needs depend on your age, sex, height, weight, and activity level. The Mifflin-St Jeor equation calculates your Basal Metabolic Rate (BMR) — the calories your body burns at rest — then multiplies by an activity factor to estimate Total Daily Energy Expenditure (TDEE). Most adults need between 1,600 and 3,000 calories per day. Our calorie calculator provides a personalized estimate based on your specific measurements.
Body fat percentage is the proportion of your total weight that is fat tissue. It provides a more complete picture than BMI because it accounts for muscle mass. You can estimate it using the US Navy method (waist, neck, and hip circumference measurements) or from your BMI. Essential fat is 2-5% for men and 10-13% for women; athletic ranges are 6-13% for men and 14-20% for women.
The general guideline is about half your body weight in ounces (e.g., 150 lbs = 75 oz), but actual needs vary based on exercise intensity, climate, altitude, and pregnancy status. Hot weather, high altitude, and vigorous exercise can increase needs by 50% or more. Our water intake calculator factors in all of these variables to give you a personalized daily target in ounces, liters, and cups.
Yes, completely. Every health calculator on ThisCalc runs 100% in your browser using JavaScript. Your weight, height, body measurements, and other health data never leave your device. There is no server processing, no accounts, no cookies tracking your inputs, and no database storing your information. You can verify this by checking your browser's network tab while using any calculator.