What Are Health & Fitness Calculators?
Health and fitness calculators are tools that use clinically validated mathematical formulas to estimate key health metrics — such as how many calories your body burns, your ideal body weight, your body fat percentage, and your optimal hydration needs. These calculators take your personal data (age, height, weight, activity level) and apply scientific equations to give you actionable insights without needing a lab or gym assessment.
How to Use These Calculators
Start with the BMI Calculator to assess your current weight category. Then use the TDEE Calculator to find your daily calorie needs, and the Macro Calculator to determine your protein, carbs, and fat targets based on your goal. Pair these with the Water Intake Calculator for hydration and the Sleep Calculator for recovery optimization.
Formulas Used
All calculators use industry-standard equations:
- BMR/TDEE/Calorie/Macro: Mifflin-St Jeor equation (most accurate for general population)
- Body Fat: US Navy method (circumference measurements)
- Ideal Weight: Devine, Hamwi, Robinson, and Miller formulas
- Water Intake: 35 ml/kg baseline + activity and climate adjustments
- Sleep: 90-minute sleep cycle model (National Sleep Foundation)
- Pregnancy: Naegele's Rule (LMP + 280 days)
Frequently Asked Questions
Are these health calculators accurate?
These calculators use established scientific formulas and provide reliable estimations for most people. However, they are not substitutes for professional medical advice. Individual results may vary based on genetics, medical conditions, and other factors that formulas cannot capture.
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest — just to keep vital organs functioning. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor, representing your total daily calorie burn including exercise and normal daily movement.
How do I calculate my macros?
Use our Macro Calculator. It first calculates your TDEE, then splits calories into protein, carbs, and fat based on your goal. For weight loss: typically 35% protein / 35% carbs / 30% fat. For muscle gain: 30% protein / 50% carbs / 20% fat. For maintenance: 30% protein / 40% carbs / 30% fat.
How much water should I drink per day?
The general guideline is 8 cups (2 liters) per day, but actual needs vary significantly. Our Water Intake Calculator personalizes this based on your weight (baseline: 35 ml per kg), activity level, climate, and whether you are pregnant or nursing.
What are sleep cycles and why do they matter?
Sleep cycles last approximately 90 minutes each and cycle through light sleep, deep sleep (NREM), and REM sleep. Waking up in the middle of a deep sleep cycle causes grogginess, even after 8 hours. Our Sleep Calculator finds optimal wake times that align with cycle completion, so you wake up refreshed.