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Fitness calculators that read your body's numbers.
BMI, BMR, calories burned, body fat and target heart rate — five instruments, one page, instant results.
Fitness tracking starts with a handful of core numbers: how much you weigh relative to your height, how many calories your body burns at rest, how hard a workout actually costs you, and what heart rate zone gets you the training effect you're after. The five calculators on this page cover that ground. Each uses a standard, widely-cited formula — the Mifflin-St Jeor equation for resting metabolic rate, the U.S. Navy circumference method for body fat, and the Karvonen method for heart rate zones — so the numbers you get here line up with what a trainer or a doctor's office would tell you. Enter your details once per calculator and the reading updates instantly as you adjust the inputs.
Frequently asked questions
What counts as a healthy BMI?
A BMI between 18.5 and 24.9 is generally classified as a healthy weight range. BMI is a quick screening tool based on height and weight only, so it doesn't account for muscle mass — very muscular people can show a higher BMI without carrying excess fat.
How accurate is a BMR calculator?
The Mifflin-St Jeor equation used here is considered one of the more accurate predictive formulas for resting metabolic rate, typically within about 10% of a lab-measured value for most adults. It's a solid starting point for setting calorie targets, not a substitute for metabolic testing.
How is body fat percentage estimated without calipers?
This calculator uses the U.S. Navy method, which estimates body fat from neck, waist (and hip, for women) circumference measurements plus height. It's a reasonably reliable field method, though DEXA scans or hydrostatic weighing remain more precise.
What heart rate zone should I train in?
It depends on the goal: 50–60% of heart rate reserve is a warm-up/recovery zone, 60–70% builds aerobic base and fat oxidation, 70–80% is a solid cardio zone, and 80–90% is a peak/interval zone. The calculator above shows your personal ranges based on age and resting heart rate.
