BMR Calculator: Find Your Basal Metabolic Rate and Daily Calorie Needs
Your basal metabolic rate is the foundation of every calorie target you will ever be given. Get it right, and your deficit, maintenance, and surplus numbers all fall into place. This calculator uses the Mifflin–St Jeor equation — the most accurate predictive formula for the general population — to calculate your BMR and total daily energy expenditure, then maps those figures to practical calorie targets for weight loss, maintenance, and muscle gain.
What Is BMR?
Your basal metabolic rate (BMR) is the number of calories your body burns each day to keep you alive at complete rest. It covers everything your body does without you thinking about it: breathing, circulating blood, maintaining body temperature, repairing cells, and running organ function. BMR accounts for roughly 60–75% of most people’s total daily calorie burn — far more than exercise.
BMR is determined primarily by your body size, lean muscle mass, age, and sex. Men generally have higher BMRs than women due to greater muscle mass. Younger individuals tend to have higher BMRs than older individuals, though the decline is largely driven by muscle loss rather than ageing itself. The Mifflin–St Jeor formula used in this calculator estimates BMR from your height, weight, age, and sex with reasonable accuracy for the general population.
What Is TDEE?
Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns across a full day, accounting for your activity level on top of your BMR. It is calculated by multiplying your BMR by an activity multiplier that reflects how physically demanding your typical week is — from 1.2 for sedentary individuals to 1.9 for those with extremely active lifestyles.
TDEE is the single most important number for managing your calorie intake effectively. If you eat at your TDEE, your weight stays stable. Eat below it to lose weight; eat above it to gain weight. The accuracy of your TDEE estimate depends on how honestly you assess your activity level — most people overestimate how active they are, which leads to underestimating how large a deficit they actually need. Use TDEE as a starting estimate, then adjust based on real-world results over 2–4 weeks.
BMR vs TDEE: What’s the Difference?
BMR and TDEE measure two different things. BMR is the energy your body needs to survive in a state of complete rest — no movement, no digestion, no stress. TDEE is everything on top of that: the extra energy you burn through physical activity, non-exercise movement like walking and fidgeting (known as NEAT), and the thermic effect of food, which accounts for roughly 10% of total calorie burn.
In practice, TDEE is the number you manage your calorie intake against, not BMR. Eating at your BMR is appropriate only in a clinical setting and represents a severe restriction for anyone who moves during the day. The gap between BMR and TDEE gives you your “activity buffer” — the calories you can consume above your BMR before you start accumulating a surplus. For a moderately active person, that gap is typically 400–700 kcal per day.
How to Use Your BMR to Lose Weight
Your BMR and TDEE give you the numbers you need to set a calorie target for weight loss. The process is straightforward: start from your TDEE, then apply a calorie deficit.
A deficit of 500 kcal per day below TDEE produces approximately 0.5 kg of weight loss per week — a rate that is widely considered sustainable and muscle-sparing. A deficit of 1,000 kcal per day targets roughly 1 kg per week, which is the upper limit most dietitians recommend for healthy adults. Going beyond this accelerates muscle loss and increases the risk of metabolic adaptation, where your body reduces BMR in response to prolonged restriction.
It is important not to eat below your BMR. This represents the absolute minimum calorie requirement for bodily function, and eating below it consistently will trigger muscle catabolism, hormonal disruption, and disproportionate BMR reduction. A practical lower floor for most active adults is BMR + 200 kcal.
Pair your calorie target with adequate protein — at least 1.6–2g per kg of bodyweight — to preserve muscle during a deficit. The calorie target determines the rate of weight loss; the macro split determines the composition of what you lose.
Why Maintenance Calories Matter More Than a Diet
Most people think about calories in terms of diets — periods of restriction followed by a return to old habits. A more durable approach is to think about maintenance calories: the intake at which your weight naturally stays stable without conscious effort.
Understanding your maintenance calories changes how you approach food permanently. Once you know your TDEE, you have a reference point for every decision. You know how much you can eat on a rest day, how a large weekend meal fits into the week, and how much exercise is needed to offset a particular food choice. This nutritional literacy is far more valuable than any specific diet plan.
Maintenance phases — deliberate periods of eating at TDEE after a cut — are also an important tool in long-term weight management. They allow metabolic rate to recover, hunger hormones (leptin and ghrelin) to re-regulate, and energy levels to stabilise before the next phase of cutting begins. Spending 4–8 weeks at maintenance between cutting phases is associated with better long-term adherence and less rebound weight gain compared to extended continuous restriction.
Your maintenance calories are not fixed. They change as your body composition shifts, as your activity level changes, and as you age. Recalculating your TDEE every 6–8 weeks — or whenever your weight changes by more than 3–5 kg — keeps your targets accurate and your progress on track.
Average BMR by Age and Gender
The table below shows estimated average BMR values for UK adults at typical heights and weights, calculated using the Mifflin–St Jeor formula. Male values are based on a height of 178 cm; female values on 163 cm. Weights are taken from average UK body weight data by age group. Use these as a general reference, not a personal target — your individual result from the calculator above will be more accurate.
| Age Group | Avg Weight (M) | BMR — Male | TDEE — Male (mod.) | Avg Weight (F) | BMR — Female | TDEE — Female (mod.) |
|---|---|---|---|---|---|---|
| 20–29 | 82 kg | 1,901 kcal | 2,947 kcal | 70 kg | 1,520 kcal | 2,356 kcal |
| 30–39 | 85 kg | 1,878 kcal | 2,911 kcal | 73 kg | 1,494 kcal | 2,316 kcal |
| 40–49 | 87 kg | 1,828 kcal | 2,833 kcal | 76 kg | 1,456 kcal | 2,257 kcal |
| 50–59 | 86 kg | 1,753 kcal | 2,717 kcal | 77 kg | 1,393 kcal | 2,159 kcal |
| 60–69 | 83 kg | 1,643 kcal | 2,547 kcal | 74 kg | 1,309 kcal | 2,029 kcal |
| 70+ | 79 kg | 1,531 kcal | 2,373 kcal | 70 kg | 1,222 kcal | 1,894 kcal |
TDEE calculated at moderately active (×1.55). Male height: 178 cm. Female height: 163 cm. Values rounded to nearest kcal.
Frequently Asked Questions
What is a normal BMR?
A normal BMR varies significantly depending on body size, age, and sex. For an average adult male in the UK, BMR typically falls between 1,600 and 1,900 kcal per day. For an average adult female, the range is roughly 1,300 to 1,600 kcal per day. Larger, younger, and more muscular individuals will have higher BMRs. These figures represent the calories your body burns at complete rest — before any activity is accounted for.
How accurate is the Mifflin–St Jeor formula?
The Mifflin–St Jeor formula is widely regarded as the most accurate predictive equation for BMR in the general population. Research comparing it against indirect calorimetry — the gold-standard clinical measurement — found that it predicts BMR within approximately 10% for most people. It outperforms older equations such as the Harris–Benedict in both accuracy and consistency. That said, no formula can account for individual metabolic variation. Use the result as a starting point and adjust based on real-world progress over 2–4 weeks.
Does muscle mass increase BMR?
Yes. Skeletal muscle is metabolically active tissue that burns calories at rest, whereas fat tissue burns very few. Adding 1 kg of lean muscle increases resting energy expenditure by roughly 13 kcal per day. While this figure sounds modest, the cumulative effect of consistent resistance training over years — and the associated increase in muscle mass — meaningfully raises BMR and makes long-term weight management considerably easier. It is also worth noting that more muscular people have higher TDEEs, giving them more calorie headroom while dieting.
Does BMR decrease with age?
Yes. BMR typically declines by roughly 1–2% per decade from the mid-twenties onward. This is largely driven by sarcopenia — the age-related loss of lean muscle mass — rather than ageing itself. Individuals who maintain muscle mass through resistance training experience a much smaller decline. The Mifflin–St Jeor formula accounts for this by incorporating age as a variable, reducing the BMR estimate as age increases.
How can I increase my BMR?
The most effective strategies are: (1) building lean muscle mass through progressive resistance training, since muscle is metabolically expensive to maintain; (2) eating sufficient protein, as the thermic effect of protein is significantly higher than carbohydrates or fat; (3) avoiding prolonged severe calorie restriction, which causes the body to down-regulate metabolic rate as a survival response; and (4) prioritising sleep quality, as poor sleep is consistently associated with reduced resting energy expenditure and impaired recovery.
What is TDEE?
TDEE stands for Total Daily Energy Expenditure — the total number of calories your body burns in a day, accounting for all physical activity on top of your BMR. It is calculated by multiplying your BMR by an activity factor that reflects your typical weekly movement, ranging from 1.2 for sedentary individuals to 1.9 for those with extremely demanding physical lives. TDEE is the number you compare your food intake against to determine whether you are in a calorie deficit, at maintenance, or in a surplus.
What are maintenance calories?
Maintenance calories is another term for TDEE — the calorie intake at which your body weight stays stable over time. If you eat exactly your maintenance calories, you will neither gain nor lose weight. Maintenance is not a fixed number; it shifts as your weight, activity level, and body composition change. Many people find it useful to spend deliberate periods eating at maintenance to stabilise weight, reset hunger hormones, and restore metabolic rate after a prolonged cut.
How do I lose 1 kg per week using my BMR?
One kilogram of body fat contains approximately 7,700 kcal of stored energy. To lose 1 kg per week, you need to create a deficit of around 7,700 kcal over seven days — approximately 1,100 kcal per day below your TDEE. For most people, this is an aggressive target that risks muscle loss and metabolic adaptation. A more sustainable approach is 0.5 kg per week, requiring a daily deficit of roughly 500–550 kcal. This calculator shows both deficit levels as concrete calorie targets.
Should I eat my BMR calories?
Your BMR represents the absolute minimum calorie intake needed to sustain basic physiological functions at rest. Eating at or below your BMR is not advisable for anyone who is active, as it leaves no energy for movement, digestion, or recovery. Even on an aggressive cut, calorie intake should remain above BMR. The NHS recommends a minimum of 1,200 kcal per day for women and 1,500 kcal per day for men when dieting, though most active individuals should eat considerably more than this.
What is the difference between BMR and RMR?
BMR (Basal Metabolic Rate) is measured under highly controlled conditions — complete rest, fasted state, neutral temperature, and no recent physical exertion. RMR (Resting Metabolic Rate) is measured under less stringent conditions and typically runs 10–20% higher than true BMR because it includes some low-level activity and ongoing digestion. In practice, most online calculators — including this one — calculate something closer to RMR under the label ‘BMR’, and the terms are widely used interchangeably. For everyday tracking purposes, the distinction rarely matters.
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