Best Free Health and Fitness Calculators 2026 — BMI, Body Fat, TDEE, Macros and More

A healthy BMI falls between 18.5 and 24.9 according to WHO classifications. Below 18.5 is considered underweight, 25 to 29.9 is overweight, and 30 or above is classified as obese. BMI is a useful screening tool but does not distinguish between muscle and fat, so athletes and muscular individuals may register as overweight despite being lean.

The US Navy body fat method estimates body fat percentage from neck, waist, and hip measurements. Studies show it is accurate to within 3-4% of results from more expensive methods like DEXA scans for most people. It tends to be less accurate for very lean or very overweight individuals. For tracking changes over time, consistency in how you take the measurements matters more than absolute accuracy.

TDEE stands for Total Daily Energy Expenditure, the total number of calories your body burns in a day including exercise and daily activity. It is calculated by first finding your Basal Metabolic Rate (BMR) using formulas like Mifflin-St Jeor, then multiplying by an activity factor ranging from 1.2 (sedentary) to 1.9 (very active). Your TDEE is the calorie target for weight maintenance.

A safe and sustainable calorie deficit is 500 calories below your TDEE, which produces roughly 0.5 kg (1 lb) of fat loss per week. Deficits larger than 1,000 calories per day are generally not recommended as they can cause muscle loss, fatigue, and nutrient deficiencies. Calculate your TDEE first, then subtract 500 to get your daily target.

A common macro split for fat loss is 40% protein, 30% carbohydrates, and 30% fat. High protein intake (around 1.6-2.2 g per kg of body weight) helps preserve muscle mass during a calorie deficit. The exact carb and fat split matters less than hitting your calorie and protein targets consistently.

Most adults need 5 to 6 complete sleep cycles per night, where each cycle lasts approximately 90 minutes. That works out to 7.5 to 9 hours of sleep. Waking up between cycles rather than in the middle of one helps you feel more rested. The Sleep Calculator finds bedtimes and wake-up times aligned to these 90-minute cycles.