Free bmr calculator
See how many calories your body burns at rest. Enter your height, weight, age, and sex and the calculator returns your basal metabolic rate using the Mifflin-St Jeor equation, plus your daily calorie needs at every activity level — updated live, as you type.
On this page16 sections
| Activity | × | Calories / day |
|---|---|---|
| Sedentary · little or no exercise | 1.2 | 2,039 cal/day |
| Lightly active · 1–3 days/week | 1.375 | 2,336 cal/day |
| Moderately active · 3–5 days/week | 1.55 | 2,633 cal/day |
| Very active · 6–7 days/week | 1.725 | 2,930 cal/day |
| Athlete · twice daily / physical job | 1.9 | 3,228 cal/day |
BMR is an estimate; individual metabolism varies. How accurate is this?
Results are estimates. Consult a professional.
How the BMR calculator works
Your basal metabolic rate is the number of calories your body burns at complete rest — lying still, awake, fasted, in a comfortable room — just to keep you alive. Breathing, circulating blood, building and repairing cells, and running your brain and organs account for the large majority of the energy you spend each day, before you move a muscle. The calculator estimates that floor from four inputs: your sex, age, height, and weight. It plugs them into the Mifflin-St Jeor equation, the predictive formula clinicians and dietitians reach for most often, and returns your daily resting calorie burn.
What the number means
The result is your maintenance baseline at zero activity: the calories you would burn if you spent the entire day resting. It is not the amount you should eat, because almost nobody lies still for 24 hours. Standing, walking, working, and exercising all add to it. Think of your BMR as the foundation; your real daily calorie need is that foundation plus everything you do on top of it.
BMR vs RMR vs TDEE
Three acronyms get tangled together in calorie planning, and keeping them straight makes the rest easy. Picture them stacked: BMR is the strict resting floor, RMR sits just above it in real measurement, and TDEE is the whole stack — everything you actually burn once movement, work, exercise, and digestion are added in. It is TDEE, not BMR, that tells you how much to eat.
BMR and RMR differ only in how they are measured — the everyday distinction is small, and the Mifflin-St Jeor equation predicts both. The bigger jump is from BMR to TDEE: you multiply your resting burn by an activity factor that matches a typical day. The busier you are, the higher the multiplier, and the further your real needs sit above your resting floor.
| Activity level | Multiplier | What it means |
|---|---|---|
| Sedentary | 1.2 | Desk job, little or no exercise |
| Lightly active | 1.375 | Light exercise or sport 1–3 days a week |
| Moderately active | 1.55 | Moderate exercise 3–5 days a week |
| Very active | 1.725 | Hard exercise or sport 6–7 days a week |
| Athlete | 1.9 | Twice-daily training or a physical job plus exercise |
These are the standard activity factors paired with the Mifflin-St Jeor equation to estimate TDEE. TDEE = BMR × activity factor.
For a full breakdown of your daily needs, including a deficit or surplus for losing or gaining weight, use the TDEE calculator or the calorie calculator. If you prefer the older formula, the Harris-Benedict calculator estimates the same BMR a different way — all of them build on the resting figure shown here.
A worked example using the BMR calculator
Daniel is 30, stands 175 cm, and weighs 75 kg. He wants to know how many calories he burns at rest before adding any activity. Here is the arithmetic the calculator runs through the men's Mifflin-St Jeor equation.
Step 1 — Weight and height terms
10 × 75 = 750, and 6.25 × 175 = 1,093.75.
Step 2 — Age term and the male constant
5 × 30 = 150, which is subtracted, and the men's formula adds +5 at the end.
Step 3 — Add it all up
750 + 1,093.75 − 150 + 5 = 1,698.75, which rounds to about 1,699 calories a day at complete rest.
When to use a BMR calculator
BMR is the starting point for almost any calorie-based plan. Knowing your resting burn turns vague goals into concrete daily numbers. Reach for it when you want to:
- Plan weight loss — find your maintenance calories first, then subtract a sustainable deficit to lose fat steadily.
- Plan weight or muscle gain — find maintenance, then add a modest surplus to build mass without excess fat.
- Set a daily calorie target — combine your BMR with an activity factor to get a realistic intake goal for the day.
- Understand your metabolism — see roughly how many calories your body needs just to function, and how age, size, and muscle change that.
Why BMR differs for men and women
Look at the two formulas and you will spot the only difference: men add a constant of +5 at the end, women subtract 161. At the same age, height, and weight, that gap puts a man's estimated BMR about 166 calories a day above a woman's. It is not an arbitrary penalty — it is the equation's way of accounting for body composition.
On average, at an identical weight, men carry more lean muscle and less fat than women, whose bodies hold more essential fat for hormonal and reproductive health. Muscle is metabolically active tissue that burns more energy at rest than fat does, so a more muscular body has a higher resting burn. The two constants are the average correction Mifflin and colleagues measured between the sexes. They are estimates of a typical difference, not a rule about any individual — a very muscular woman can easily out-burn a sedentary man.
Average BMR by age and sex
There is no single "normal" BMR — it scales with your size, sex, and age, so a higher number simply reflects a bigger or more muscular body, not better health. As a rough reference, the average adult man's BMR is around 1,700 calories a day and the average adult woman's around 1,400. Two patterns hold across almost everyone: men run higher than women of the same build, and BMR drifts down through adult life.
| Age | Men | Women |
|---|---|---|
| 20 | ≈ 1,820 cal/day | ≈ 1,440 cal/day |
| 30 | ≈ 1,770 cal/day | ≈ 1,390 cal/day |
| 40 | ≈ 1,720 cal/day | ≈ 1,340 cal/day |
| 50 | ≈ 1,670 cal/day | ≈ 1,290 cal/day |
| 60 | ≈ 1,620 cal/day | ≈ 1,240 cal/day |
| 70 | ≈ 1,570 cal/day | ≈ 1,190 cal/day |
Illustrative figures from the Mifflin-St Jeor equation, holding a reference build (men 80 kg / 178 cm, women 68 kg / 164 cm) and varying age. Your own number depends on your weight and height — use the calculator above for a personal estimate.
What affects your BMR
Two people of the same age and weight can have noticeably different resting burns. Several factors push BMR up or down:
- Muscle mass — lean muscle burns more calories at rest than fat does, so a more muscular body has a higher BMR. This is the single factor you can most change, through resistance training.
- Body size — a larger body has more tissue to maintain, so taller and heavier people generally have a higher BMR.
- Age — BMR tends to decline through adulthood, largely because muscle mass falls and body fat rises with the years.
- Sex — men usually have a higher BMR than women of the same size, reflecting their larger average share of muscle.
- Genetics — inherited differences mean some people simply run a faster or slower metabolism than others of similar build.
- Hormones and thyroid — thyroid hormones set the body's metabolic pace; an underactive thyroid lowers BMR and an overactive one raises it.
Can you change your BMR?
Yes — but far less than the supplement aisle would have you believe. The internet is full of promises to "boost your metabolism" with green tea, ice baths, cayenne pepper, or tiny meals eaten every two hours. The honest picture is that most of these move BMR by single-digit percentages at best, and many do nothing measurable at all. Your resting burn is set mainly by your body size and composition, and those are what actually shift it.
What genuinely moves the needle
- Build lean muscle. This is the one real lever. Muscle is metabolically active tissue, and adding it through resistance training raises your resting burn — the effect is modest per kilogram but compounds and lasts.
- Don't crash-diet for long. Extended aggressive deficits prompt the body to defend itself by lowering resting burn and shedding muscle — so under-eating to "speed things up" backfires. Build deficits from your TDEE, never below your BMR.
- Eat enough protein. Protein costs the most energy to digest and supports the muscle that drives BMR, so it helps on both fronts during weight loss.
What's mostly overblown
- "Metabolism-boosting" foods and supplements. Caffeine and capsaicin (chili) nudge calorie burn slightly and briefly; the effect is too small to matter for weight, and tolerance builds quickly.
- Eating many small meals. Meal frequency does not change your total daily burn — six small meals and three larger ones with the same calories burn the same energy digesting.
- "Starvation mode" as an excuse. Metabolism does adapt downward in a deficit, but not enough to stop weight loss entirely if the deficit is real. Plateaus are far more often a calorie-tracking problem than a broken metabolism.
How to use your BMR result well
Treat the number as a well-grounded estimate, not a precise measurement. The Mifflin-St Jeor equation is built from population averages, so any individual result can sit roughly ten percent above or below the truth. A few habits keep it useful:
- Don't eat below your BMR for long. Dropping intake under your resting needs for extended periods can cost muscle, stall progress, and leave you under-fuelled. Build deficits from your TDEE, not your BMR.
- Recalculate as your weight changes. BMR depends on body size, so update the figure every few kilograms rather than holding an old number.
- Always pair it with activity. Multiply by an activity factor to reach your real daily need before setting any calorie target.
- Adjust against real results. Use the estimate as a starting point, then nudge intake up or down based on how your weight actually moves over two or three weeks.
BMR calculator definitions
How accurate is this BMR calculator?
The arithmetic is exact, and the formula behind it is the best of the common options. When the American Dietetic Association compared the major predictive BMR equations, the Mifflin-St Jeor formula came out as the most accurate for adults, which is why clinicians and dietitians favour it. But "most accurate" is not the same as "exact". Like all equations that predict metabolism from height, weight, age, and sex, it works from population averages and cannot see your individual body composition — so any single estimate can land roughly 10% above or below your true resting burn.
The gold standard for measuring BMR is indirect calorimetry, a lab test that measures the oxygen you consume and the carbon dioxide you produce to calculate your real energy expenditure. No formula matches it. For everyday planning, though, the calculator's estimate is more than good enough: use it as your starting figure, pair it with an activity factor for your total daily needs, and refine it against how your weight actually changes over a few weeks. For a fuller picture of your body, the BMI calculator sits alongside this one.
Formula and sources
BMR is estimated with the Mifflin-St Jeor equation (Mifflin MD, St Jeor ST, et al., A new predictive equation for resting energy expenditure in healthy individuals, American Journal of Clinical Nutrition, 1990) from your sex, age, height, and weight. The American Dietetic Association's 2005 review of predictive equations identified it as the most reliable for adults, which is why it is the default here rather than the older Harris-Benedict equation. Daily-need estimates apply the standard activity factors (1.2 sedentary to 1.9 athlete) to turn BMR into total daily energy expenditure.
Mifflin-St Jeor equation, American Journal of Clinical Nutrition (1990); American Dietetic Association review of predictive resting-energy equations (2005).Frequently asked questions about the free bmr calculator
About this BMR calculator
This BMR calculator runs entirely in your browser. Your height, weight, age, and sex never leave your device — nothing is sent to a server, logged, or shared. It uses the Mifflin-St Jeor equation (the most accurate common predictive formula per the American Dietetic Association) and multiplies by standard activity factors to estimate your daily calorie needs, updating instantly.
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