BMR (Basal Metabolic Rate) Calculator

Use our basal metabolic rate (BMR) calculator to estimate how many calories your body needs to carry out vital functions at rest, such as breathing, temperature regulation, and pumping blood.

Just enter your age, sex, height, weight, and activity level to instantly gain a better understanding of what your body needs to function.

Your basal metabolic rate (BMR) is the minimum number of calories your body needs to carry out essential, life-sustaining functions, like breathing, circulation, and digestion, while at rest. It accounts for around 60 to 75% of the calories you burn each day.

Several factors can affect your BMR, including your age, sex, weight, and body composition. BMR is not the same as body mass index (BMI), which uses your height and weight measurements to estimate whether you are at a healthy weight.

Knowing your BMR can help you manage your weight more effectively by giving you a baseline number of calories your body needs before daily activity.

BMR can be calculated using several formulas, including the Harris-Benedict formula, but the most common modern method is the Mifflin-St Jeor equation. It uses your age, sex, height, and weight to estimate your BMR using the following equations:

• Men – (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5
• Women – (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161

Our BMR calculator also asks for your activity level, which does not change your BMR but will help you estimate how many calories you burn in total, known as your Total Daily Energy Expenditure (TDEE). It will also tell you your BMI. All of these figures are useful for building an effective and sustainable weight management plan.

Your BMR is the number of calories your body needs to perform essential functions, such as breathing and cell repair, while at rest. Although it represents your minimum needs, it’s also a helpful starting point for planning your calorie intake depending on whether you want to lose, gain, or maintain weight.

BMR for weight loss

If your goal is to lose weight, you’ll need to eat fewer calories than your body burns each day, also known as a calorie deficit. Your BMR gives you an estimate of how much energy your body needs at rest.

In practice, your daily calorie needs are higher than your BMR because you also burn calories through physical activity and digestion. Once you estimate your total daily energy expenditure (TDEE), you can create a moderate calorie deficit, typically around 300 to 600 calories per day, which may support gradual and sustainable weight loss of around 0.5 to 1kg per week for many people.

However, it’s generally not recommended to eat below your BMR, as doing so may make it difficult for your body to meet its basic physiological needs.

BMR for weight gain

If you’re looking to gain weight or build muscle, you’ll need to eat more calories than your body burns (calorie deficit).

Using your BMR as a starting point, estimate your daily calorie needs and then add a small calorie surplus, typically around 250 to 500 extra calories per day. This can help support gradual weight gain while minimising excessive fat gain. Combining a calorie surplus with regular resistance training can help ensure that more of the weight gained comes from muscle rather than body fat.

BMR for weight maintenance

If you’re happy with your current weight, you’ll need to keep the number of calories you eat and the calories you burn balanced.

By understanding your baseline needs, you can then factor in your daily activity level to estimate your total energy needs. By consuming around the same number of calories you burn, you’ll help to keep your weight stable.

BMR is not the same for everyone. Several biological, physiological, and lifestyle factors can influence the number of calories the body needs at rest. Understanding these factors can help explain why some people have lower or higher BMR values.

Age

BMR tends to decrease with age as people lose muscle mass and become less active. Because muscle burns more calories than fat, muscle loss can slow your resting metabolic rate.

Sex

BMR values tend to vary between men and women, with men having a higher BMR due to increased muscle mass and less fat. A study published in 2023 found that the average BMR for men and women was:

• 1552 calories for men
• 1327 calories for women

This suggests that men need, on average, more than 200 additional calories to support vital functions at rest.

Body composition

People with more muscle mass and lean tissue naturally burn more calories at rest. That means that 2 people who weigh the same but one has more muscle while the other has more fat can have different BMR values.

One way to improve your BMR is to build or maintain muscle mass through strength training, especially during weight loss.

Hormones

Hormones that regulate metabolism can also affect BMR. For example, thyroid hormones play a key role in controlling how quickly your body uses energy. Conditions that affect hormone levels, such as an underactive or overactive thyroid, may change your metabolic rate.

Lifestyle

Certain lifestyle habits may influence your metabolic rate over time. For example, regular physical activity, particularly strength training, can help increase muscle mass, which may raise BMR. On the other hand, long periods of inactivity or prolonged calorie restriction may contribute to a lower metabolic rate as the body adapts to conserve energy.

Body weight

People with larger bodies generally have a higher BMR because they have more cells and tissues that require energy to function. This means taller or heavier individuals often burn more calories at rest than smaller individuals.

You might consider recalculating your BMR every 4 to 6 weeks or if:

• your body weight changes by at least 5%
• the amount of exercise you do changes
• you start weight loss medication or any medication that can affect your weight
• you hit a weight loss plateau

Recalculating your BMR is particularly useful if you are on a weight loss programme, as it will give you a more accurate idea about how many calories you need to help you reach your goals.