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Calorie Calculator

Calculate your BMR and daily calorie needs based on the Mifflin-St Jeor equation.

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Your Details

The Mifflin-St Jeor formula uses different constants for men and women due to differences in average muscle mass.

years

Your age in years. BMR decreases with age — most people burn fewer calories per decade after 30.

ft
in

Taller people have higher calorie needs because they have more body surface area and muscle mass to maintain.

lbs

Your current body weight. Use your weight without shoes or heavy clothing for the most accurate result.

Most people overestimate their activity level. If in doubt, choose one level lower than you think — it's a common source of error.

Your Daily Calories

BMR (at rest)
Basal Metabolic Rate
1,847
TDEE (Maintenance)
To maintain current weight
2,540
Weight Loss (−500 cal)
~1 lb/week loss
2,040
Aggressive Loss (−1000 cal)
~2 lbs/week loss
1,540
Muscle Gain (+300 cal)
Lean bulk surplus
2,840
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Frequently Asked Questions

What is BMR and how is it calculated?
BMR stands for Basal Metabolic Rate — the number of calories your body burns at complete rest just to maintain basic physiological functions like breathing, circulation, and cell repair. This calculator uses the Mifflin-St Jeor equation, the most widely validated formula for estimating BMR. For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161.
What is TDEE?
TDEE stands for Total Daily Energy Expenditure — the total number of calories you burn in a day when your activity level is factored in. It's calculated by multiplying your BMR by an activity factor: 1.2 for sedentary (desk job, little exercise), 1.375 for lightly active (1–3 days/week), 1.55 for moderately active (3–5 days/week), 1.725 for very active (6–7 days/week), and 1.9 for extremely active (physical job or 2x/day training). TDEE represents the calorie amount needed to maintain your current weight.
How many calories should I eat to lose weight?
A calorie deficit is required for weight loss. A moderate deficit of 500 calories per day below your TDEE produces roughly 1 pound of weight loss per week, which is widely recommended as a sustainable rate. A 1,000 calorie/day deficit targets 2 pounds per week, but can be difficult to sustain and may cause muscle loss without adequate protein intake. This calculator shows targets for moderate (500 cal deficit) and aggressive (1,000 cal deficit) weight loss as a starting point.
How many calories should I eat to gain muscle?
Building muscle requires a calorie surplus — eating more than your TDEE. A modest surplus of 200–500 calories per day is recommended for lean muscle gain, minimizing fat gain. Larger surpluses ("dirty bulking") build muscle faster but accumulate significantly more fat. Combined with resistance training and sufficient protein intake (around 0.7–1g per pound of body weight), a surplus of 300–500 calories is an effective starting point for most people.
Are these calorie calculations accurate?
The Mifflin-St Jeor equation is the most accurate widely-used formula for estimating metabolic rate, but like all formulas it provides an estimate. Individual variation in metabolism can be 10–20% above or below the estimate. The activity multipliers are also approximations. Use these numbers as a starting point, track your actual weight change over 2–4 weeks, and adjust calories up or down by 100–200 to fine-tune based on real-world results.
Does my age affect how many calories I need?
Yes, significantly. BMR decreases with age due to changes in body composition (reduced muscle mass), hormonal changes, and slower cellular metabolism. Most people see a measurable drop in TDEE each decade after age 30. This is one reason why eating habits that maintained a healthy weight in your 20s may lead to gradual weight gain in your 40s and 50s without adjustment. Regular resistance training can help offset age-related muscle loss and metabolic decline.
How does gender affect calorie needs?
Men generally have higher BMR and TDEE than women of the same height, weight, and age. This is primarily due to men having more skeletal muscle mass on average, which is metabolically more active than fat tissue. Hormonal differences also play a role. Women also experience metabolic changes during pregnancy, lactation, and menopause that affect calorie needs. The Mifflin-St Jeor formula accounts for gender through different constant offsets in the equation.
What should I do with these calorie numbers?
Use your TDEE as a daily calorie target to maintain your current weight. To lose weight, aim for 300–500 calories below TDEE and track your food intake using an app like Cronometer or MyFitnessPal. Prioritize protein (to preserve muscle), fill the rest with nutrient-dense whole foods, and combine with exercise. Weigh yourself weekly (not daily) and adjust intake based on trends. For personalized advice, especially with health conditions, always consult a registered dietitian.

Understanding Calories, BMR, and TDEE

A calorie is a unit of energy. Specifically, it's the amount of energy needed to raise the temperature of one gram of water by one degree Celsius. Your body burns calories every second — even while you sleep — to keep your heart beating, your lungs breathing, and your brain running.

Your Basal Metabolic Rate is the number of calories you'd burn if you stayed completely motionless for 24 hours. For a 35-year-old woman who is 5'5" and weighs 145 pounds, the Mifflin-St Jeor equation gives a BMR of approximately 1,440 calories. This is the floor — the minimum your body needs just to survive. The Mifflin-St Jeor formula is the most validated equation for general use and is preferred over the older Harris-Benedict formula by most dietitians today.

Total Daily Energy Expenditure takes your BMR and multiplies it by an activity factor to account for how much you actually move. The same woman at a sedentary desk job has a TDEE of about 1,728 calories. Working out 3–4 days per week brings it to around 1,980. This is the number that actually matters for weight management — it represents your daily maintenance level.

The 3,500-calories-per-pound rule is a rough approximation, not a precise formula. Real weight loss is messier — your metabolism adapts to calorie restriction over time, which is why progress tends to slow after the first few weeks even when you haven't changed anything. A 500-calorie daily deficit generally produces about 1 pound of loss per week initially. Sustained deficits tend to produce slower results as the body adjusts.

Eating below 1,200 calories per day (for women) or 1,500 (for men) without medical supervision tends to backfire. Your body responds to severe restriction by reducing muscle mass and slowing metabolism. Moderate sustained deficits — 300 to 500 calories below TDEE — produce better long-term results than aggressive cuts.

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About This Calorie Calculator

This calculator uses the Mifflin-St Jeor equation, the gold standard formula recommended by the American Dietetic Association for estimating Basal Metabolic Rate. It was validated in a comprehensive 2005 study comparing five BMR equations and consistently outperformed alternatives like the Harris-Benedict equation in accuracy across diverse populations.

Your height and weight are converted from US to metric units for the calculation. The resulting BMR is then multiplied by your selected activity factor to produce your TDEE—your total daily calorie burn. From there, the calorie targets for weight loss and gain are straightforward adjustments above or below maintenance. All calculations happen in your browser with no data sent to any server.