BMR Calculator UK – Calculate Your Basal Metabolic Rate
BMR Calculator UK: Calculate Your Basal Metabolic Rate
Use our free BMR calculator UK to estimate how many calories your body burns at rest. Enter your age, height, weight and sex used by the equation to calculate your basal metabolic rate using the Mifflin-St Jeor formula.
The calculator also estimates your total daily energy expenditure (TDEE), helping you understand how your activity level affects your daily calorie requirements.
Free BMR Calculator
Enter your measurements below to estimate your basal metabolic rate.
The Mifflin-St Jeor equation uses sex-specific coefficients. These estimates may be less accurate for people taking gender-affirming hormones.
Activity multipliers are approximate. Your actual energy expenditure may differ.
What Is Basal Metabolic Rate?
Basal metabolic rate, usually abbreviated to BMR, is the amount of energy your body needs to maintain essential physiological functions while at rest. It represents the energy required to keep your body functioning even when you are not exercising or performing everyday activities.
Your body uses energy continuously. Your heart needs energy to pump blood, your lungs require energy to support breathing, and your brain consumes energy to maintain its normal functions. Your liver, kidneys and other organs also contribute to your resting energy expenditure.
Maintaining body temperature, supporting cellular processes and repairing tissues all require energy. These processes continue throughout the day and night, including when you are asleep.
BMR is commonly expressed as the number of kilocalories your body uses in 24 hours under standardised resting conditions. In everyday nutrition, kilocalories are usually referred to simply as calories.
For example, an estimated BMR of 1,600 calories means that your body is predicted to require approximately 1,600 kilocalories per day under basal conditions.
It does not mean that you should necessarily eat 1,600 calories each day. Most people need additional energy for movement, digestion, exercise and other daily activities.
How Does Our BMR Calculator Work?
The Pryhelm BMR calculator uses the Mifflin-St Jeor equation. This predictive equation estimates resting metabolic rate using body weight, height, age and sex.
It was developed from measurements of resting energy expenditure and is widely used in nutrition and fitness settings.
Although the equation is often described as a BMR formula, it is more precisely an estimator of resting metabolic rate. True basal metabolic rate is measured under more restrictive laboratory conditions.
Mifflin-St Jeor Formula for Men
Mifflin-St Jeor Formula for Women
The calculator automatically converts imperial measurements into kilograms and centimetres before applying the formula.
Because the equation is predictive, the result should be interpreted as an estimate rather than an exact measurement of your metabolism.
BMR Calculation Example
Consider a 30-year-old man who weighs 75 kg and is 175 cm tall.
Using the Mifflin-St Jeor equation:
BMR = (10 × 75) + (6.25 × 175) − (5 × 30) + 5
BMR = 750 + 1,093.75 − 150 + 5
BMR = 1,698.75 calories per day
The estimated resting energy requirement is therefore approximately 1,699 calories per day.
This is the predicted amount of energy needed under resting conditions. Actual daily energy requirements are generally higher because most people move, work, digest food and perform other activities.
What Is the Difference Between BMR and TDEE?
BMR and total daily energy expenditure are related measurements, but they describe different aspects of energy use.
BMR represents the energy required for essential physiological functions under basal conditions.
Total daily energy expenditure, abbreviated to TDEE, represents the total amount of energy your body uses throughout a day.
TDEE includes resting energy expenditure, physical activity, the energy required to digest and process food, and other components of daily energy use.
For practical estimates, a common approach is to multiply resting energy expenditure by an activity factor.
For example, someone with an estimated BMR of 1,700 calories and an activity multiplier of 1.55 would have an estimated TDEE of 2,635 calories per day.
This calculation provides a starting point for understanding energy requirements. It is not a direct measurement of the calories an individual burns.
BMR Activity Levels Explained
Our calculator includes five activity categories. These are commonly used multipliers for estimating daily energy expenditure from resting energy requirements.
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Little exercise and predominantly seated activities. |
| Lightly active | 1.375 | Light exercise approximately 1–3 days per week. |
| Moderately active | 1.55 | Moderate exercise approximately 3–5 days per week. |
| Very active | 1.725 | Frequent exercise or substantial physical activity. |
| Extra active | 1.9 | Very demanding training or highly physical daily activity. |
These descriptions are general guides. Two people who exercise the same number of days per week may have substantially different energy requirements.
Exercise intensity, session duration, occupation, daily step count and individual physiology all affect energy expenditure.
What Factors Affect Your BMR?
Several factors influence resting energy expenditure. Some are included in predictive equations, while others are not.
1. Body Size
Larger bodies generally require more energy to maintain essential physiological functions. This is one reason weight and height are included in the Mifflin-St Jeor equation.
2. Muscle Mass
Lean body mass is an important contributor to resting energy expenditure. People with greater amounts of lean tissue may have higher resting energy requirements.
However, the relationship between muscle mass and metabolism is more complicated than the idea that every additional kilogram of muscle burns a large number of calories each day.
3. Age
Resting energy requirements can change with age. Changes in body composition, organ function and activity may all contribute to these differences.
Age is included directly in the Mifflin-St Jeor equation, although individual changes cannot be predicted perfectly from age alone.
4. Sex and Body Composition
The Mifflin-St Jeor equation includes different coefficients for men and women. These reflect average differences in the populations used to develop the predictive equation.
Individual body composition can vary considerably, so the equation may overestimate or underestimate the resting energy requirements of a particular person.
5. Health and Physiological Conditions
Illness, fever, certain medications, hormonal changes and other physiological factors can influence energy expenditure.
Pregnancy and breastfeeding can also change nutritional requirements. A general adult BMR calculator is not designed to calculate the additional energy needs associated with these conditions.
Can You Use BMR for Weight Loss?
Understanding your estimated BMR can help you learn how your body uses energy, but BMR alone should not be used to determine a weight-loss calorie target.
Your total daily energy expenditure is generally more relevant when considering overall energy balance.
If your energy intake is consistently lower than your energy expenditure, your body may draw on stored energy. However, changes in body weight are not perfectly predictable from a simple calorie calculation.
Energy expenditure can change as body weight changes. Appetite, physical activity, fluid balance and other physiological adaptations can also affect progress.
A calculated calorie deficit should therefore be treated as an initial estimate rather than a guarantee of a particular rate of weight loss.
People who are underweight, pregnant, breastfeeding, recovering from illness or living with an eating disorder should seek appropriate professional advice before attempting intentional weight loss.
Can BMR Help With Muscle Gain?
BMR can contribute to an estimate of daily energy requirements for people who undertake resistance training or other forms of exercise.
Someone who wants to gain muscle may use estimated TDEE as one piece of information when planning their overall nutrition.
However, muscle development depends on several factors, including progressive resistance training, adequate nutrition, sufficient protein intake and recovery.
A BMR calculator cannot determine how much muscle someone will gain or establish an individually optimal calorie intake.
Training experience, body composition, exercise programming and individual responses also influence results.
How Accurate Is a BMR Calculator?
Predictive equations are useful because they provide accessible estimates without requiring specialised equipment.
However, a calculated BMR is not the same as a laboratory measurement.
Resting metabolic rate can be measured using indirect calorimetry, which estimates energy expenditure from respiratory gas exchange.
Predictive equations may be less accurate for individuals whose body composition or physiological circumstances differ substantially from those represented in the original study populations.
Examples include some highly muscular athletes, people with substantial changes in body composition and individuals with particular medical conditions.
The activity multiplier introduces additional uncertainty into TDEE calculations because physical activity varies from day to day.
For these reasons, the results should be used as general estimates. Where precise nutritional assessment is necessary, a qualified healthcare professional or registered dietitian can provide individual guidance.
BMR Calculator UK: Metric and Imperial Units
Our calculator supports both metric and imperial measurements to make it convenient for UK visitors.
You can enter your weight in kilograms and height in centimetres, or use stone, pounds, feet and inches.
Imperial measurements are converted to metric units before the Mifflin-St Jeor equation is applied.
The calculator uses the following standard conversions:
- 1 pound = 0.45359237 kilograms.
- 1 stone = 14 pounds.
- 1 inch = 2.54 centimetres.
- 1 foot = 12 inches.
Both measurement options use the same underlying formula. The choice of units does not change the calculation method.
Frequently Asked Questions
What is a normal BMR?
There is no single normal BMR that applies to every adult. Resting energy requirements vary with body size, age, body composition and other individual characteristics.
A higher or lower calculated BMR does not automatically indicate better or worse health.
Is BMR the number of calories I should eat?
No. BMR estimates the energy required under resting conditions. Your daily energy needs also include movement, digestion and physical activity.
Estimated TDEE is generally more relevant when considering total daily energy requirements.
Does exercise increase BMR?
Exercise increases energy expenditure during the activity and can influence body composition over time. Resistance training may increase lean body mass, which contributes to resting energy expenditure.
However, the effect on BMR varies between individuals and cannot be predicted from exercise frequency alone.
Does BMR decrease with age?
Resting energy expenditure can change with age, partly because body composition and other physiological factors may change.
The relationship is not identical for everyone. Maintaining physical activity and muscle strength can support health as people age.
Is BMR the same as resting metabolic rate?
The terms are often used interchangeably in everyday fitness discussions, but they are not technically identical.
BMR is measured under tightly controlled basal conditions, whereas resting metabolic rate is measured under somewhat less restrictive resting conditions.
The Mifflin-St Jeor equation estimates resting metabolic rate.
Can I calculate BMR without knowing my body fat percentage?
Yes. The Mifflin-St Jeor equation uses age, height, weight and sex. It does not require a body fat percentage measurement.
Other predictive equations may use lean body mass or additional measurements.
Can I use this calculator during pregnancy?
This general adult calculator does not account for the additional energy requirements associated with pregnancy or breastfeeding.
Pregnant and breastfeeding individuals should seek appropriate advice about their nutritional requirements rather than relying on this estimate.
Can teenagers use this BMR calculator?
This calculator is intended for adults aged 18 and over. Children and teenagers have different nutritional requirements, particularly during periods of growth and development.
Paediatric energy requirements should be assessed using age-appropriate methods.
How often should I recalculate my BMR?
You may wish to recalculate your estimated BMR after a meaningful change in body weight or other relevant measurements.
Small day-to-day fluctuations in body weight do not necessarily represent meaningful changes in resting energy expenditure.
Can a BMR calculator diagnose a slow metabolism?
No. A predictive equation cannot diagnose a metabolic disorder or establish whether an individual's measured metabolism is unusually slow.
If you have persistent symptoms or concerns about your metabolism, speak to an appropriate healthcare professional.
References and Further Reading
The following resources provide additional information about energy requirements, nutrition and physical activity.
- Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990;51(2):241–247. Read the original study .
- NHS: Healthy weight .
- NHS: Exercise and physical activity .
- NHS: Healthy eating .
This calculator is provided for general educational and informational purposes only. It does not provide medical advice, diagnose health conditions or prescribe an individual calorie intake.
The results are estimates based on a predictive equation and general activity multipliers. They may not accurately represent your individual energy requirements.
Consult a qualified healthcare professional or registered dietitian if you require personalised nutritional advice, particularly if you have a medical condition, are pregnant or breastfeeding, or have a history of disordered eating.
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