Health & Fitness Calculators
Free health and fitness calculators for BMI, calories, pregnancy, ideal weight, body fat, and wellness tracking.
About Health & Fitness Calculators
Your health metrics tell a story. A 5'8" person weighing 170 lbs has a BMI of 25.8 (overweight), but if they lift weights with 15% body fat, they're healthier than someone at 150 lbs with 28% body fat (BMI 22.8, "normal"). A 30-year-old woman at 150 lbs needs 2,160 calories/day to maintain weight—eating just 1,660 calories creates a 500-calorie deficit for losing 1 lb/week. Our health and fitness calculators show you the real numbers behind your health, not generic advice that ignores your body's unique needs.
BMI Calculator: Understanding Body Mass Index
The BMI Formula
BMI (Body Mass Index) is calculated using your weight and height with this formula:
BMI = weight (kg) / height² (m²) For imperial units: BMI = [weight (lbs) / height² (inches²)] × 703
Real Example Calculation
Person weighing 180 lbs at 5'10" tall (70 inches):
- Square the height: 70 × 70 = 4,900 square inches
- Divide weight by height²: 180 ÷ 4,900 = 0.0367
- Multiply by 703: 0.0367 × 703 = 25.8
- Result: BMI of 25.8 (Overweight category)
BMI Categories:
- Underweight: BMI below 18.5 (health risks include weakened immune system, nutrient deficiencies)
- Normal weight: BMI 18.5-24.9 (lowest health risk category)
- Overweight: BMI 25-29.9 (increased risk for heart disease, diabetes)
- Obese: BMI 30+ (significantly higher risk for chronic diseases)
BMI Limitations: BMI doesn't measure body composition. A 5'10" male bodybuilder at 200 lbs with 10% body fat has BMI 28.7 (overweight), but they're extremely healthy. An elderly person at 5'10" and 160 lbs (BMI 23.0, normal) might have dangerously low muscle mass. Use BMI as a screening tool, not a definitive health measure.
Calorie Calculator: How Many Calories Do You Need?
BMR and TDEE Formulas
Your Total Daily Energy Expenditure (TDEE) starts with Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation:
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5 Women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161 TDEE = BMR × Activity Multiplier: - Sedentary (little/no exercise): BMR × 1.2 - Light (1-3 days/week): BMR × 1.375 - Moderate (3-5 days/week): BMR × 1.55 - Very Active (6-7 days/week): BMR × 1.725 - Extremely Active (athlete, 2x/day): BMR × 1.9
Step-by-Step Calculation Example
30-year-old woman, 150 lbs (68 kg), 5'5" (165 cm), moderate activity:
- Calculate BMR: (10 × 68) + (6.25 × 165) - (5 × 30) - 161 = 680 + 1,031 - 150 - 161 = 1,400 calories/day
- Apply activity multiplier: 1,400 × 1.55 (moderate activity) = 2,170 calories/day (TDEE)
- For weight loss (1 lb/week): 2,170 - 500 = 1,670 calories/day
- For weight gain (0.5 lb/week): 2,170 + 250 = 2,420 calories/day
Why 500 calories = 1 lb/week? One pound of body fat contains approximately 3,500 calories. Create a deficit of 500 calories/day: 500 × 7 days = 3,500 calories = 1 lb lost per week. This is the maximum safe rate for sustainable fat loss while preserving muscle.
Calorie Targets by Goal
For our example (30F, 150 lbs, TDEE 2,170):
- Aggressive fat loss (2 lbs/week): 1,170 calories/day (1,000 deficit) - not recommended long-term, minimum 1,200 for women
- Standard fat loss (1 lb/week): 1,670 calories/day (500 deficit) - sustainable, preserves muscle
- Slow cut (0.5 lb/week): 1,920 calories/day (250 deficit) - easiest to stick with, minimal hunger
- Maintenance: 2,170 calories/day (no deficit) - maintains current weight
- Lean bulk (0.5 lb/week): 2,420 calories/day (250 surplus) - builds muscle with minimal fat gain
Pregnancy Due Date Calculator
How Due Dates Are Calculated
Pregnancy due dates use Naegele's Rule: Add 280 days (40 weeks) to the first day of your last menstrual period (LMP).
Due Date = LMP + 280 days Or: LMP + 1 year - 3 months + 7 days Example: LMP: January 1, 2026 Due Date: January 1, 2027 - 3 months + 7 days = October 8, 2026
Pregnancy Timeline Example (LMP: January 1, 2026):
- Conception: ~January 15, 2026 (week 2 of pregnancy, ovulation typically day 14)
- Positive pregnancy test: ~January 29, 2026 (4 weeks pregnant)
- First ultrasound: ~February 26, 2026 (8 weeks, confirm due date)
- End of first trimester: March 26, 2026 (12 weeks, morning sickness usually improves)
- Anatomy scan: May 21, 2026 (20 weeks, check baby's development)
- Viability: June 18, 2026 (24 weeks, baby could survive with medical support)
- Third trimester: July 16, 2026 (28 weeks, rapid weight gain)
- Full term: September 17, 2026 (37 weeks, safe for delivery)
- Due date: October 8, 2026 (40 weeks)
Accuracy note: Only 5% of babies are born on their exact due date. 90% are born between 37-42 weeks. First-time mothers average 40 weeks + 5 days. Your doctor may adjust your due date after ultrasound measurements.
Body Composition: Beyond the Scale
Body Fat Percentage Ranges
Your body fat percentage matters more than scale weight. Two people at the same weight can look completely different based on body composition:
Men's Body Fat Categories:
- Essential fat: 2-5% (minimum for basic physiological function, dangerous to maintain)
- Athletes: 6-13% (visible abs, very lean, competitive bodybuilders pre-contest 5-7%)
- Fitness: 14-17% (athletic appearance, some ab definition)
- Average: 18-24% (healthy for general population)
- Obese: 25%+ (increased health risks)
Women's Body Fat Categories:
- Essential fat: 10-13% (minimum for reproductive function, dangerous to maintain)
- Athletes: 14-20% (lean, athletic, visible muscle definition)
- Fitness: 21-24% (healthy, toned appearance)
- Average: 25-31% (healthy for general population)
- Obese: 32%+ (increased health risks)
Example comparison: Two 5'6" women both weigh 140 lbs. Woman A has 20% body fat (28 lbs fat, 112 lbs lean mass)—she looks athletic and toned. Woman B has 32% body fat (45 lbs fat, 95 lbs lean mass)—she looks soft despite same weight. The 17 lbs difference in lean mass completely changes appearance.
Ideal Weight Ranges
For a 5'8" person, ideal weight formulas suggest:
- Robinson formula (1983): Men 154 lbs, Women 140 lbs
- Devine formula (1974): Men 156 lbs, Women 141 lbs
- Miller formula (1983): Men 157 lbs, Women 141 lbs
- Hamwi formula (1964): Men 158 lbs, Women 143 lbs
These formulas average to 140-158 lbs for this height, but body composition matters more. A 170 lb person with 15% body fat is healthier than a 145 lb person with 30% body fat.
Macronutrient Targets
For our 30-year-old woman example (150 lbs, 1,670 calories for fat loss):
High Protein Approach (best for muscle retention during fat loss):
- Protein: 150g (1g per lb body weight) = 600 calories (36%)
- Fat: 55g (0.35g per lb, minimum for hormones) = 495 calories (30%)
- Carbs: 144g (remaining calories) = 575 calories (34%)
Why these numbers? High protein (0.8-1g per lb) preserves muscle during weight loss, increases satiety, and has highest thermic effect (30% of calories burned during digestion). Minimum fat (0.3-0.4g per lb) supports hormone production. Remaining calories from carbs fuel workouts and daily activity.
Health isn't about following generic advice—it's about understanding your specific numbers. Calculate your BMI, TDEE, and body composition targets above, then adjust based on how you feel and your real-world results. Your body's feedback matters more than any formula.
Frequently Asked Questions
How accurate are these health calculators?
Our health calculators use evidence-based formulas and medical standards to provide estimates. However, they are educational tools only and should not replace professional medical advice. Individual results vary based on factors like genetics, medical conditions, and lifestyle. Always consult with a healthcare provider for personalized health guidance.
What is BMI and why does it matter?
BMI (Body Mass Index) is a measure of body fat based on height and weight. While it's a useful screening tool, it doesn't directly measure body fat or account for muscle mass, bone density, or distribution of fat. It should be one of several factors considered when evaluating health, not the only metric.
How do I calculate my daily calorie needs?
Your daily calorie needs depend on your Basal Metabolic Rate (BMR) - the calories you burn at rest - multiplied by your activity level. Our calorie calculator uses the Mifflin-St Jeor equation, which factors in age, weight, height, gender, and activity level to provide a personalized estimate.
Can I lose weight just by counting calories?
While creating a calorie deficit is essential for weight loss, sustainable results come from a combination of balanced nutrition, regular physical activity, adequate sleep, and stress management. Focus on the quality of calories (nutrient-dense whole foods) not just quantity.
How is pregnancy due date calculated?
The due date is typically calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). Our pregnancy calculator uses this method and can also calculate based on conception date or ultrasound results. Keep in mind that only about 5% of babies are born on their exact due date.
Should I trust my fitness tracker's calorie burn estimates?
Fitness trackers provide useful estimates but can vary in accuracy. They tend to overestimate calorie burn, especially for low-intensity activities. Use them as a general guide for tracking trends and activity levels rather than precise measurements. Our calculator provides a baseline that you can adjust based on real-world results.