Why Use Our Health Calculators
24 free health calculators that show the formula they use and where the numbers come from: CDC, NIH, WHO, ACOG, the National Academies and the 2024 Compendium of Physical Activities. Results are estimates to help you plan, not a diagnosis.
Every health calculator on this page follows official guidelines. The BMI calculator uses WHO classifications. The calorie and TDEE calculator uses the Mifflin-St Jeor equation, the most validated formula for estimating metabolic rate. The pregnancy due date calculator uses standard 40-week gestational calculations confirmed by ACOG.
Use these tools together for a complete picture. Start with the BMI calculator for body composition context, then the calorie calculator for your daily energy needs, and the ideal weight calculator to set realistic goals.
All calculations run in your browser. No health data is ever stored or transmitted. Always consult a healthcare professional before making significant changes to diet or exercise.
Which Calculator Answers Your Question
| Your question | Use this |
|---|---|
| Is my weight in a healthy range? | BMI Calculator, Ideal Weight Calculator |
| How many calories should I eat? | Calorie Calculator, Calorie Deficit Calculator |
| How much protein, carbs and fat? | Macro Calculator |
| When is my baby due? | Pregnancy Due Date Calculator |
| When am I most fertile? | Ovulation Calculator |
| When should I go to bed? | Sleep Cycle Calculator |
| How many calories did my workout burn? | Calories Burned Calculator |
| What pace do I need for my race goal? | Running Pace Calculator |
Reference Values Worth Knowing
| Measure | Reference value |
|---|---|
| Healthy adult BMI | 18.5 to 24.9 (25 to 29.9 overweight, 30 and above obesity) |
| Physical activity for adults | 150 to 300 minutes of moderate activity a week, plus muscle strengthening on 2 days |
| Sleep for adults 18 to 60 | 7 hours or more a night |
| Total water intake (food and drinks) | About 3.7 L a day for men and 2.7 L for women |
| Waist-to-hip ratio linked to higher risk | 0.90 or more for men, 0.85 or more for women |
| US standard drink | 14 g of pure alcohol (12 oz beer at 5%, 5 oz wine at 12%, 1.5 oz spirits at 40%) |
| Legal driving limit | 0.08% BAC in every state except Utah (0.05%) |
| Pregnancy length | 280 days (40 weeks) from the first day of the last period |
These values describe populations, not individuals. For decisions about your health, talk to a doctor, midwife or registered dietitian.
Sources. CDC adult BMI categories and sleep recommendations; Physical Activity Guidelines for Americans, 2nd edition (HHS); National Academies Dietary Reference Intakes for water; WHO waist circumference and waist-hip ratio report; NIAAA standard drink definition; NHTSA and Utah Code on BAC limits; ACOG Committee Opinion 700.
Health & Fitness Questions
What is a healthy BMI for adults?
For adults, a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese. BMI is weight in kg divided by height in meters squared. Use the BMI Calculator for an instant result in metric or imperial.
How many calories should I eat per day to lose weight?
To lose 1 lb per week, create a 500-calorie daily deficit from your TDEE. Most adults need 1,600 to 2,400 calories/day depending on age, sex, weight, and activity. Never go below 1,200 cal (women) or 1,500 cal (men) without medical guidance. Use the Calorie / TDEE Calculator for your exact number.
What is a normal BMR for my age?
Average BMR is roughly 1,400 to 1,800 cal/day for women and 1,600 to 2,200 for men, declining about 2% per decade after 30. The Mifflin-St Jeor equation: (10 x kg) + (6.25 x cm) - (5 x age) + 5 (men) or -161 (women). Use the BMR Calculator for your exact baseline.
How do I calculate my body fat percentage?
The US Navy method uses circumference measurements: neck + abdomen (men), neck + waist + hips (women). Healthy ranges: men 10 to 20%, women 18 to 28%. Athletes: 6 to 13% (men), 14 to 20% (women). Use the Body Fat Calculator for the Navy method or BMI-based estimate.
How do I calculate my pregnancy due date?
Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. If you know conception date, add 266 days instead. Only about 5% of babies are born exactly on their due date. Use the Pregnancy Due Date Calculator for LMP, conception, or IVF transfer date methods.
How many calories does walking burn per hour?
A 155 lb person burns roughly 280 calories/hour at 3.5 mph, 350 at 4 mph, and 420 at 4.5 mph. Formula: METs x weight (kg) x hours. Walking METs range from 3.5 (moderate) to 5 (brisk). Use the Calories Burned Calculator for your exact weight and pace.
What is the ideal weight for my height?
Devine formula: men: 50 kg + 2.3 kg per inch over 5 ft; women: 45.5 kg + 2.3 kg per inch over 5 ft. A 5’10” man has ideal weight of ~166 lbs. BMI 18.5 to 24.9 is the broader healthy range. Use the Ideal Weight Calculator to compare multiple formulas side by side.
How do I calculate my ovulation date?
Ovulation occurs 14 days before your next period, not 14 days after. For a 28-day cycle that is day 14; for a 32-day cycle, day 18. The fertile window is 5 days before ovulation plus ovulation day. Use the Ovulation Calculator with your last period date and average cycle length.
What is a healthy waist size?
Keep waist circumference less than half your height (waist-to-height ratio below 0.5). Health risks rise above 35 inches for women and 40 inches for men. These thresholds are linked to cardiovascular and metabolic disease. Use the Waist-to-Hip Ratio Calculator for a fuller assessment.
How much water should I drink per day?
General guidelines: 3.7 liters (125 oz) for men and 2.7 liters (91 oz) for women daily from all sources. Simpler estimate: body weight in lbs divided by 2 = daily oz needed. Add 12 oz per 30 minutes of exercise. Use the Water Intake Calculator for a personalized recommendation.