How the Calorie Calculator Works

This calculator estimates your daily calorie needs in two steps. First, it calculates your Basal Metabolic Rate (BMR), the number of calories your body burns at rest just to keep you alive -- breathing, circulating blood, and maintaining organ function. Then it multiplies your BMR by an activity factor that reflects how much you move throughout the day. The result is a personalized calorie target you can use for weight loss, maintenance, or muscle gain.

The Mifflin-St Jeor Equation

This calculator uses the Mifflin-St Jeor equation, which is widely considered the most accurate predictive formula for estimating BMR in healthy adults. Published in 1990, it has been validated by numerous studies and is recommended by the Academy of Nutrition and Dietetics over older methods.

For Men

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

For Women

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

The older Harris-Benedict equation, developed in 1919 and revised in 1984, tends to overestimate calorie needs by about 5%, which can make it less useful for people trying to manage their weight precisely. The Mifflin-St Jeor equation corrects for this and provides a more reliable baseline.

Understanding Activity Levels

Your activity level determines the multiplier applied to your BMR. Choosing the right level is important for getting an accurate estimate.

Sedentary (x1.2) -- Desk job with little or no exercise. You spend most of the day sitting and do not follow a regular workout routine.
Lightly Active (x1.375) -- Light exercise or walking 1 to 3 days per week. This includes casual gym sessions, short walks, or light household activity.
Moderately Active (x1.55) -- Moderate exercise 3 to 5 days per week. You follow a consistent workout routine such as weight training, jogging, or group fitness classes.
Very Active (x1.725) -- Hard exercise 6 to 7 days per week. You train intensely most days and may have an active job or participate in sports.
Extra Active (x1.9) -- Very intense daily training or a physically demanding job. This level is typical for competitive athletes, construction workers, or anyone with both a physical job and a regular training schedule.

If you are unsure, start with a lower activity level. You can always adjust up if you find you are losing weight too quickly or feeling low on energy.

Calories for Your Goals

Once you know your maintenance calories, you can adjust your intake based on your goal.

Weight Loss: A deficit of about 500 calories per day below maintenance will lead to roughly 1 pound (0.45 kg) of fat loss per week. This is a sustainable pace that helps preserve muscle mass. Aggressive deficits above 750 to 1,000 calories are harder to maintain and increase the risk of muscle loss, fatigue, and nutrient deficiencies.
Maintenance: Eating at your estimated maintenance level keeps your weight stable. This is useful for body recomposition, where you slowly build muscle while staying at the same weight.
Muscle Gain: A surplus of about 250 to 500 calories per day above maintenance supports muscle growth when combined with resistance training. A moderate surplus of 250 to 300 calories minimizes fat gain while still providing enough fuel for muscle recovery and growth.

Keep in mind that these are estimates. Track your weight for 2 to 3 weeks and adjust your calories by 100 to 200 if you are not seeing the expected results. Individual metabolism, non-exercise activity, and other factors can influence your actual needs.