BMR Calculator

Your basal metabolic rate is the energy your body burns doing absolutely nothing — keeping the heart beating, lungs breathing, and temperature stable. It is the foundation every calorie plan is built on, and this calculator estimates it three different ways so you can see both the number and how much the choice of formula matters.

Mifflin-St Jeor is the default: the equation research has rated most reliable for modern general populations and the one dietitians typically use. Harris-Benedict (the classic equation, in its revised 1984 form) is included for comparison and tends to read slightly higher. Katch-McArdle takes a different route entirely — it estimates from lean body mass, so it asks for your body-fat percentage and rewards you with a more personalized figure if that number is accurate. A field for body fat appears only when you select it.

Because BMR alone is a floor rather than a budget, the results include a table of your estimated total daily burn (TDEE) at five activity levels, from sedentary (×1.2) to athlete (×1.9). That is the number calorie targets should be set against — and the Calorie Calculator continues from exactly this point, adding goal-based targets and macros. As with every calculator in this category, the figures are population estimates within roughly ±10%, clearly disclaimed as education rather than medical advice, and computed entirely in your browser.

Each formula estimates resting energy burn from a different angle:

• Mifflin-St Jeor: 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 for men, and the same with −161 for women. Comparison research has rated it the most reliable standard equation for the general population.
• Harris-Benedict (revised 1984): the classic early-20th-century equation with updated coefficients; it typically reads slightly higher than Mifflin.
• Katch-McArdle: 370 + 21.6 × lean body mass (kg), where lean mass is computed from your body-fat percentage. Because it works from composition rather than total weight, it is the better fit for lean, muscular people — provided the body-fat number is accurate.

The TDEE table then multiplies the BMR by standard activity factors: 1.2 sedentary, 1.375 light (1–3 workouts/week), 1.55 moderate (3–5), 1.725 very active (6–7), and 1.9 for athletes. TDEE, not BMR, is the number to set eating targets against.

All three equations are population averages: genetics, hormones, thyroid function, and body composition create individual differences the formulas cannot see, so expect roughly ±10% accuracy for most adults. Katch-McArdle inherits any error in your body-fat estimate. The activity multipliers are coarse bands, and the figures are educational rather than prescriptive — the tool's own disclaimer directs anyone with a medical condition or history of disordered eating to a doctor or registered dietitian before setting calorie goals.

Client-side calculation with metric canonical state. Formula implementations: Mifflin-St Jeor with the ±5/−161 sex constants; revised Harris-Benedict (1984) coefficients (88.362/13.397/4.799/5.677 male, 447.593/9.247/3.098/4.330 female); Katch-McArdle as 370 + 21.6 × lean mass, with body fat clamped to 0–70%. Activity multipliers 1.2–1.9. Validation requires positive weight and height and age between 1 and 119. Results are rounded to whole kilocalories for display.

The three formulas at a glance

For the same person the three typically span 50–150 kcal — a useful reminder that every BMR figure is an estimate.

Anyone starting a diet or training plan who wants the baseline number done properly; lifters and athletes who want a lean-mass-based estimate; and the curious who want to see why their calorie needs differ from a friend's. If you want the full plan — goal calories and macro grams — the Calorie Calculator and Macro & TDEE Calculator build directly on this foundation.