Calorie Calculator

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to keep you alive — breathing, circulating blood, maintaining body temperature, and running basic cell function — with zero physical activity factored in. TDEE (Total Daily Energy Expenditure) takes that baseline and adds the calories you burn from daily activity, exercise, and general movement, giving a realistic estimate of your actual total calorie burn in a normal day. TDEE is the more directly useful number for weight management, since it represents your true maintenance calories — eating exactly your TDEE keeps your weight stable, while eating above or below it drives weight gain or loss.

Mifflin-St Jeor (published in 1990) is widely regarded by dietitians and researchers as the most accurate BMR formula for the general population, and it's the formula the Academy of Nutrition and Dietetics recommends over older alternatives like the Harris-Benedict equation (from 1919, later revised in 1984). Studies comparing formulas against indirect calorimetry (the gold-standard lab measurement of actual metabolic rate) have consistently found Mifflin-St Jeor produces the smallest average error across a broad range of body types, which is why it's become the standard formula in modern nutrition calculators and clinical practice.

Mifflin-St Jeor is the best widely-available formula, but it's still an estimate based on population averages — actual metabolic rate varies between individuals due to factors no formula can fully capture, like genetics, muscle mass, hormone levels, and metabolic adaptation from past dieting. Studies generally find it accurate within about 10% for most people, which is a solid starting estimate but not a substitute for tracking your actual weight change over 2-3 weeks at a given calorie level and adjusting from there — that real-world feedback loop is always more accurate than any formula alone, since it accounts for your specific body's response.

Be honest rather than aspirational — this is the single biggest source of error in calorie calculations, since people commonly overestimate their activity level. Sedentary means a desk job with little deliberate exercise (most office workers who don't exercise regularly fall here, even if they feel generally busy). Light means structured exercise 1-3 days a week on top of a normal daily routine. Moderate means 3-5 days a week of real exercise. Active and Very Active are for people exercising hard nearly every day, or combining serious training with a physically demanding job — genuinely fewer people qualify for these top two tiers than tend to select them. When in doubt, pick the lower of two options you're considering, then adjust upward later based on your real-world results.

A calorie deficit of about 500 calories per day corresponds to roughly 1 pound (0.45 kg) of fat loss per week, since one pound of body fat represents approximately 3,500 stored calories — so a 1000-calorie daily deficit targets a faster ~2 pounds (0.9 kg) per week. This tool floors every calorie target at 1000 calories per day as a basic safety guardrail, but a 1000-calorie deficit is aggressive and not appropriate for everyone, especially those with a lower TDEE to begin with (a smaller person's 'fast' deficit can approach an unsafe absolute calorie level even after the floor). Rapid, large deficits also increase the risk of muscle loss, nutrient deficiency, and metabolic slowdown. Sustainable fat loss of 0.5-1% of body weight per week (generally matching the 'Lose Weight' option here) is what most nutrition professionals recommend for most people; consult a doctor or registered dietitian before pursuing aggressive or prolonged calorie deficits.

This tool uses a higher protein percentage (35%) for both weight-loss goals, since adequate protein intake is well-supported by research to help preserve lean muscle mass during a calorie deficit — you lose more of what you diet with less muscle loss when protein is prioritized. Maintenance uses a balanced, moderate split (30% protein, 40% carbs, 30% fat), a commonly recommended general-purpose ratio. The gaining goals shift toward a higher carb percentage (45%), since carbohydrates are an efficient, readily-available fuel source for the increased training volume typically paired with a calorie surplus. These are sensible general-purpose defaults, not a personalized prescription — individual needs vary by training style, body composition goals, and personal preference, and many people successfully eat outside these exact ratios.

Yes — BMR and TDEE both change as your weight changes, since both formulas use your current body weight as a direct input. As you lose weight, your BMR (and therefore your calorie targets) genuinely decreases, because a smaller body requires fewer calories to maintain, which is exactly why weight loss commonly slows down over time even while sticking to the same calorie target. Recalculating every 5-10 pounds (2-5 kg) of weight change, or every few weeks during an active diet or bulk, keeps your targets aligned with your body's actual current needs rather than an outdated starting point.

No. Every calculation happens entirely inside your browser using plain JavaScript — there is no server-side component involved in processing your age, weight, height, or any other input at any point, which you can confirm by watching your browser's network tab while using the tool. Nothing you enter is stored, logged, or transmitted anywhere.