Basal Metabolic Rate & Daily Calorie Calculator

What the basal metabolic rate actually is

Your basal metabolic rate is the minimum energy your body needs to stay alive at rest — running your heart, brain, kidneys, and the constant turnover of tissue. It is the floor beneath everything else you do.

For most people it accounts for the majority of daily calories burned. That surprises people who assume exercise dominates the equation. Unless you train intensely or work a physical job, the calories you burn deliberately are a modest addition to a much larger baseline — which is precisely why exercise alone so often disappoints as a weight loss strategy.

Which equation this uses, and why

The best-known formula is the Harris-Benedict equation, published in 1919 and used for the better part of a century. It has a known weakness: in overweight and obese people it overestimates resting energy expenditure, typically by at least five percent.

Since roughly two thirds of adults in the United States are overweight, that bias matters. This calculator therefore uses the Mifflin-St Jeor equation, derived from indirect calorimetry in 498 healthy adults and published in the American Journal of Clinical Nutrition in 1990:¹

• Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
• Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

A 2005 systematic review in the Journal of the American Dietetic Association compared the published equations head to head and found Mifflin-St Jeor predicted resting metabolic rate within 10% of the measured value in more people — obese and non-obese alike — than any other.² That is why it is the one here.

And the activity factor

Total daily energy expenditure is your BMR multiplied by a physical activity level (PAL). The values here come from the FAO/WHO/UNU expert consultation on human energy requirements, which defines the bands as 1.40–1.69 for sedentary and light activity, 1.70–1.99 for moderately active, and 2.00–2.40 for vigorously active.³

What you picked	Multiplier	FAO band
Sedentary	1.45	1.40–1.69
Lightly active	1.60	1.40–1.69
Moderately active	1.85	1.70–1.99
Very active	2.10	2.00–2.40
Extremely active	2.30	2.00–2.40

The activity factor is the least reliable part of this calculation and the part you control, so choose it honestly. Moving one row down the table changes the answer by roughly 250–350 calories a day — more than any other input on the form. Most people overestimate: two gym sessions and a dog walk is not "moderately active."

A worked example

A 38-year-old woman, 165 cm, 68 kg, moderately active:

• BMR = (10 × 68) + (6.25 × 165) − (5 × 38) − 161
  = 680 + 1,031 − 190 − 161 = 1,360 kcal/day at complete rest.
• Maintenance = 1,360 × 1.85 = 2,516 kcal/day.
• To lose about a pound a week = 2,516 − 500 = 2,016 kcal/day.

Who this is wrong for

• Athletes and very muscular people. The equation knows your weight, not what it is made of. Muscle burns more at rest than fat, so a lean, heavily trained person is routinely underestimated — one review found prediction equations perform poorly in this group specifically.
• Anyone with a thyroid disorder. Untreated hypothyroidism lowers metabolic rate and hyperthyroidism raises it, by amounts no height-and-weight formula can see.
• People who have lost a lot of weight. After substantial loss, measured metabolic rate sits below what the equation predicts for the new body — adaptive thermogenesis — and that gap can persist for years.
• Pregnancy and breastfeeding. Both add real, changing energy requirements this does not model. Do not use the deficit figure at all.
• Children and adolescents. Different equations entirely; growth is an energy cost of its own.
• Over 80, or the seriously ill. Mifflin-St Jeor was derived in adults aged 19 to 78, and acute illness changes energy needs substantially in both directions.

How accurate is this?

It is an estimate, and worth treating as one. Formal BMR measurement assumes conditions almost nobody meets in daily life: complete muscular rest, twelve or more hours since the last meal, a thermally neutral environment, minimal emotional arousal, and being awake. Apprehension alone can raise measured BMR by fifteen to forty percent. Sleep lowers it by about ten.

Two people of identical age, sex, height, and weight can have genuinely different metabolic rates. The practical approach is to take the number as a starting estimate, eat accordingly for two or three weeks, and adjust based on what the scale actually does. Your own response is better data than any equation.

Turning this into a plan

A deficit of roughly 500 calories a day corresponds to about a pound of fat loss per week — the figure the calculator gives you above. That rule of thumb holds reasonably well at first and then slows, because a smaller body burns fewer calories and metabolism adapts downward. Plateaus are the expected behaviour of a working system, not evidence of failure.

Two things pair well with this number: finding out how many calories you actually ate today, which is almost always more than people estimate, and checking your BMI and healthy weight range so the target is realistic. The weight loss series covers the rest.

Where the macronutrient split comes from

The calculator turns your calorie target into grams of protein, fat and carbohydrate. Three decisions do all the work, and none of them is arbitrary.

Protein is set at 1.2 g per kilogram of body weight. The RDA is 0.8 g/kg, which is the amount that prevents deficiency rather than the amount that serves you well. The PROT-AGE group recommends 1.0–1.2 g/kg for healthy older adults, and the upper end of that band helps preserve muscle during weight loss [4]. So 1.2 is the top of the sensible everyday range, not a floor to beat.

You can raise it to 1.6 g/kg, and probably should not. The largest meta-analysis of resistance training and protein found gains in lean mass flattening out at about 1.6 g/kg, with no further benefit above it [5]. That number belongs to people genuinely training hard for size. Being busy, or exercising most days, is not what it describes — which is why the higher target is a checkbox with a warning rather than the default.

Fat is 25% of calories and carbohydrate is the remainder. Both sit inside the Institute of Medicine's acceptable macronutrient distribution ranges — 20–35% for fat, 45–65% for carbohydrate, 10–35% for protein [6]. A second cap holds protein to 30% of calories, which matters for anyone heavy enough that 1.2 g/kg would otherwise crowd carbohydrate below its range.

Who this split is wrong for

• Reduced kidney function. Protein targets in chronic kidney disease are set by your own clinician against your eGFR, not by body weight. Do not use this number.
• Pregnancy and breastfeeding. Both raise protein and energy needs on their own schedule. The nutrient tool handles those properly.
• Anyone below about 1,200 calories. The plan refuses to go lower and says so. Deficits that deep are a supervised undertaking.
• Endurance athletes in heavy training. Carbohydrate needs are usually expressed per kilogram per day, not as a share of calories, and can run well above what a percentage split produces.

Questions people actually ask about this

How many calories should I eat a day?

Take your BMR, multiply by the activity factor that honestly describes your week, and that is roughly your maintenance. Eat about 500 below it to lose around a pound a week. For the 38-year-old woman in the example above that is 2,516 to hold steady and about 2,016 to lose — but treat both as a starting point to adjust from after two or three weeks on the scale, not a number to obey.

What is the difference between BMR and TDEE?

BMR is what your body burns doing nothing at all — breathing, circulation, brain, kidneys, maintaining temperature. TDEE is that figure multiplied by an activity factor, so it includes everything else you do: walking to the kitchen, fidgeting, work, exercise, digesting food. BMR is the floor; TDEE is the bill.

Is the Mifflin-St Jeor equation accurate?

It is the most accurate of the widely used ones — within 10% of measured resting metabolic rate in more people than any competing equation² — but "within 10%" still means a 1,500 kcal BMR could genuinely be 1,350 or 1,650. It is a population average applied to one person, and the residual spread is real physiology, not sloppy maths.

Why is my BMR lower than a friend's who weighs the same?

Body composition, mostly. Muscle burns more at rest than fat does, so at identical height, weight, age and sex the more muscular person has the higher rate — and the equation cannot see the difference. Age matters too: BMR falls roughly 5 kcal per year in this formula, mainly because muscle is lost with age rather than because of anything mysterious.

Does eating less slow your metabolism?

Yes, and by more than the weight loss alone accounts for. Losing weight lowers BMR because there is less body to maintain, but there is an additional downward adjustment on top — adaptive thermogenesis — which can persist long after the diet ends. That is the main reason plateaus arrive and why maintenance takes ongoing effort rather than none.

Can I raise my BMR?

Meaningfully, only by adding muscle, and the effect is smaller than the internet suggests — a pound of muscle burns roughly 6 kcal a day at rest, not 50. Resistance training is still worth doing, mostly because it protects the muscle you already have while dieting, which is exactly what an aggressive deficit destroys. Metabolism-boosting foods and supplements are not a real category.

Should I eat back the calories I burn exercising?

Not if you selected an activity level that already includes that exercise — you would be counting it twice, which is the single most common error with these numbers. Either pick "sedentary" and add exercise on top, or pick the level that describes your usual week and leave it alone. Pick one method and stick to it.

Why does this give me a different number from other calculators?

Almost always the activity factor rather than the BMR. Many consumer calculators use a multiplier set running 1.2 to 1.9 that traces back to the Harris-Benedict era; this page uses the FAO/WHO/UNU physical activity levels instead.³ At the sedentary end FAO is higher; at the top end it is broadly similar. The BMR itself should match anything else using Mifflin-St Jeor to within a calorie or two.

References

The equation, the evidence for choosing it, the activity factors, and the protein and macronutrient figures.

1. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition. 1990;51(2):241–247. https://doi.org/10.1093/ajcn/51.2.241 The source of the equation used above, derived by indirect calorimetry in 498 adults aged 19 to 78.
2. Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association. 2005;105(5):775–789. https://doi.org/10.1016/j.jada.2005.02.005 Why Mifflin-St Jeor rather than Harris-Benedict: it predicted within 10% of measured RMR in more people, obese and non-obese.
3. FAO/WHO/UNU. Human Energy Requirements: Report of a Joint FAO/WHO/UNU Expert Consultation. Rome: FAO; 2004. Chapter 5, Energy requirements of adults. fao.org The physical activity level bands — 1.40–1.69, 1.70–1.99 and 2.00–2.40 — that the activity factors on this page are drawn from.
4. Bauer J, Biolo G, Cederholm T, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. J Am Med Dir Assoc. 2013;14(8):542–559. The source of the 1.0–1.2 g/kg everyday range, and of the case for the upper end of it while losing weight.
5. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376–384. Where the 1.6 g/kg ceiling comes from: gains in lean mass plateaued at about 1.62 g/kg, with no further benefit above it.
6. Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fibre, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington DC: National Academies Press; 2005. Chapter 11, Macronutrient distribution ranges. The acceptable macronutrient distribution ranges the split is held inside: 10–35% protein, 20–35% fat, 45–65% carbohydrate.