BMR Calculator

How to Use This BMR Calculator

Our BMR calculator uses the Mifflin-St Jeor equation, which is widely regarded as the most accurate formula for estimating basal metabolic rate. Enter your sex, age, height, and weight, and you'll get your BMR instantly along with a TDEE breakdown for five activity levels.

Steps:

1. Select your sex (male or female)
2. Enter your age in years
3. Enter your height in centimeters or feet/inches
4. Enter your weight in kilograms or pounds
5. Your BMR and TDEE values appear automatically

What Is BMR?

Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic, life-sustaining functions while at complete rest. These functions include breathing, circulating blood, maintaining body temperature, cell production, and organ function.

Think of BMR as your body's idle energy cost. Even if you stayed in bed all day without moving, your body would still burn this many calories just to keep you alive. For most adults, BMR accounts for 60-75% of total daily calorie expenditure.

The average BMR for adult men is around 1,600-2,000 kcal per day, and for adult women it's roughly 1,200-1,500 kcal per day. However, individual BMR varies significantly based on body composition, age, genetics, and other factors.

The Mifflin-St Jeor Formula

The Mifflin-St Jeor equation was published in 1990 and has become the standard formula used by dietitians and health professionals. It was developed from indirect calorimetry measurements and is considered more accurate than older formulas like Harris-Benedict.

For males:

BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5

For females:

BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161

Example (Male, 180 cm, 80 kg, 30 years):BMR = (10 x 80) + (6.25 x 180) - (5 x 30) + 5 = 800 + 1125 - 150 + 5 = 1,780 kcal/day

Example (Female, 165 cm, 60 kg, 28 years):BMR = (10 x 60) + (6.25 x 165) - (5 x 28) - 161 = 600 + 1031.25 - 140 - 161 = 1,330 kcal/day

BMR vs TDEE

BMR tells you how many calories you burn at rest. But nobody stays in bed all day. Your Total Daily Energy Expenditure (TDEE) accounts for everything you do: walking, working, exercising, even digesting food. TDEE is calculated by multiplying your BMR by an activity factor.

For our example male with a BMR of 1,780 kcal who exercises 4 times per week (moderately active), the TDEE would be 1,780 x 1.55 = 2,759 kcal/day. This is the number of calories he needs to maintain his current weight.

Factors That Affect BMR

Your BMR is not set in stone. Several factors can raise or lower it:

• Muscle mass. Muscle tissue is metabolically active, meaning it burns more calories at rest than fat tissue. People with more muscle mass have a higher BMR. This is why strength training is one of the most effective ways to boost your metabolism long-term.
• Age. BMR decreases by about 1-2% per decade after age 20. This is primarily due to loss of muscle mass (sarcopenia) and hormonal changes. A 60-year-old typically has a BMR that is 10-15% lower than when they were 20.
• Body size. Larger bodies require more energy to function. Taller people and heavier people naturally have higher BMRs because there is more tissue to sustain.
• Thyroid function. The thyroid gland produces hormones (T3 and T4) that directly regulate metabolic rate. Hypothyroidism (underactive thyroid) can lower BMR by 15-30%, while hyperthyroidism (overactive thyroid) can raise it significantly.
• Temperature. Your body works harder to maintain its core temperature in extreme cold or heat. BMR can increase by 5-10% in very cold environments as your body generates heat through shivering and increased metabolic activity.
• Diet and fasting.Severe calorie restriction can lower BMR by 10-20% as your body adapts to conserve energy. This is sometimes called "starvation mode," though the effect is less dramatic than popular culture suggests.

How to Use Your BMR

Knowing your BMR and TDEE is useful for several goals:

• Weight loss: Eat 300-500 kcal below your TDEE. This creates a moderate calorie deficit that leads to sustainable fat loss of about 0.5-1 lb per week.
• Weight gain (muscle): Eat 200-400 kcal above your TDEE while following a strength training program. This surplus supports muscle growth without excessive fat gain.
• Weight maintenance: Eat at your TDEE level. Track your weight over 2-3 weeks and adjust if needed, since calculated TDEE is an estimate and may need fine-tuning.

The key is to avoid extreme calorie restriction. Eating below your BMR for extended periods can lead to muscle loss, nutrient deficiencies, fatigue, and a slowed metabolism. Most dietitians recommend never eating below 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision.

Frequently Asked Questions

How accurate is the Mifflin-St Jeor equation?

The Mifflin-St Jeor formula has an accuracy of within about 10% for most people when compared to laboratory measurements via indirect calorimetry. It tends to be most accurate for non-obese individuals. For significantly overweight or obese individuals, the Katch-McArdle formula (which accounts for lean body mass) may be more accurate.

Should I eat below my BMR to lose weight?

Generally no. Eating below your BMR means you are not providing enough calories for basic bodily functions. A better approach is to eat below your TDEE but above your BMR. For example, if your BMR is 1,500 and your TDEE is 2,200, eating 1,700-1,900 calories per day creates a deficit while still fueling your body properly.

Does BMR change when I lose weight?

Yes. As you lose weight, your BMR decreases because there is less body tissue to sustain. This is why weight loss often slows over time. A person who loses 20 pounds may see their BMR drop by 80-120 kcal per day. This means you need to periodically recalculate your TDEE and adjust your calorie intake as you progress.

Can I increase my BMR?

The most effective way to increase your BMR is through building muscle mass. Each pound of muscle burns roughly 6-10 calories per day at rest, compared to about 2 calories per day for each pound of fat. Over time, gaining 10 pounds of muscle can raise your BMR by 50-80 kcal/day. High-intensity interval training (HIIT) and adequate protein intake also support a healthy metabolism.

Is BMR the same as RMR (Resting Metabolic Rate)?

They are similar but not identical. BMR is measured under strict conditions: 12 hours of fasting, 8 hours of sleep, in a dark, temperature-controlled room, and at complete rest. RMR (Resting Metabolic Rate) is measured under less restrictive conditions and is typically 10-20% higher than BMR because it includes the thermic effect of a recent meal and minimal daily activity. In practice, most calculators (including this one) estimate BMR, but the terms are often used interchangeably.