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HealthCalc provides a suite of free, science-based health calculators to help you understand and monitor your body metrics. All calculations use medically recognized formulas and run entirely in your browser for maximum privacy.
Enter your height and weight to calculate your Body Mass Index. The BMI is calculated using the standard formula: BMI = weight(kg) / height(m)ยฒ. Results are categorized according to WHO standards: Underweight (<18.5), Normal (18.5-24.9), Overweight (25-29.9), and Obese (โฅ30). The calculator also shows your ideal weight range for reference.
Estimate your daily calorie needs based on your age, gender, height, weight, and activity level. We use the Mifflin-St Jeor equation, which is considered the most accurate for estimating Basal Metabolic Rate (BMR). The tool then applies activity multipliers (sedentary: ร1.2, lightly active: ร1.375, moderately active: ร1.55, very active: ร1.725, extra active: ร1.9) to give you your Total Daily Energy Expenditure (TDEE).
Calculate your recommended daily water intake based on your weight, activity level, and climate. The general guideline is about 30-35ml per kg of body weight, adjusted upward for exercise and hot climates. Proper hydration supports digestion, skin health, energy levels, and cognitive function.
Find the optimal time to go to bed or wake up based on 90-minute sleep cycles. A complete sleep cycle includes light sleep, deep sleep, and REM stages. Waking up between cycles (rather than mid-cycle) helps you feel refreshed. The calculator accounts for the average 14 minutes it takes to fall asleep.
Enter your age and resting heart rate to calculate your five heart rate training zones using the Karvonen formula. Zone 1 (50-60% max) for recovery, Zone 2 (60-70%) for fat burning, Zone 3 (70-80%) for aerobic endurance, Zone 4 (80-90%) for anaerobic threshold, and Zone 5 (90-100%) for maximum effort.
BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat mass, so athletes may show a high BMI despite being healthy. It also doesn't account for body fat distribution. For a more complete picture, consider using BMI alongside waist circumference and body fat percentage measurements.
The Mifflin-St Jeor equation we use is estimated to be within 10% of actual metabolic rate for most people. However, individual metabolism varies based on genetics, muscle mass, hormonal factors, and more. Use the result as a starting point and adjust based on your real-world results over 2-4 weeks.
Most adults need 5-6 complete sleep cycles (7.5-9 hours) per night. However, sleep needs vary by age and individual. Teens may need 6 cycles (9 hours), while some adults function well on 5 cycles (7.5 hours). The key is to wake up at the end of a cycle rather than in the middle of one.
While Zone 2 (60-70% max HR) is often called the "fat burning zone" because a higher percentage of calories come from fat, higher intensity zones burn more total calories per minute. For weight loss, a mix of Zone 2 steady-state cardio and Zone 4 interval training is most effective. Consistency matters more than zone selection.
These calculators are designed for general wellness information and should not replace professional medical advice. They use standard, peer-reviewed formulas but cannot account for individual health conditions. Always consult with a healthcare provider for medical decisions, especially if you have existing health conditions.
The American College of Sports Medicine recommends drinking 500ml of water 2 hours before exercise, 200-300ml every 15-20 minutes during exercise, and at least 500ml after exercise for every pound of body weight lost during the workout. In hot weather, increase these amounts by 25-50%.
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