BMR Calculator
A 32-year-old woman who weighs 68 kg and stands 165 cm tall has an estimated BMR of 1,390 kcal per day. That means her body would use about 1,390 calories in a full day of complete rest to support breathing, circulation, temperature control, and basic cell function. This BMR calculator estimates basal metabolic rate with the Mifflin-St Jeor equation using sex, age, height, and weight. BMR is not the same as your full daily calorie burn. It is the baseline before walking, exercise, work, chores, digestion, and other activity raise total energy use. People often use BMR as the starting point for maintenance, fat-loss, or muscle-gain planning because it gives a cleaner rest-only estimate than guessing from body size alone. Use this calculator when you want a quick resting calorie estimate, a starting number for a TDEE calculation, or a way to compare how age, height, and weight change the estimate over time. The result is useful for planning, but it is still a formula-based estimate rather than a direct metabolic test.
Quick answer
BMR estimates the calories your body would use in about 24 hours of complete rest.
What this tells you
- •BMR estimates the calories your body would use in about 24 hours of complete rest.
- •This tool uses the Mifflin-St Jeor formula, which is one of the most common modern prediction equations for adult energy needs.
- •Weight, height, age, and sex all affect the estimate, so the result changes when any of those inputs change.
- •BMR is a starting point, not your full calorie target, because daily movement and exercise increase total energy use.
- •Real metabolism can differ from the estimate because body composition, hormones, illness, medication, and recent dieting are not included in the formula.
How to Use
- 1Choose the sex option that matches the equation you need. This tool uses separate Mifflin-St Jeor constants for female and male inputs.
- 2Enter your age in whole years. Older age lowers the estimate because the formula subtracts calories as age increases.
- 3Enter your current body weight in kilograms. If you usually track pounds, convert to kilograms first so the input matches the formula.
- 4Enter your height in centimeters. Accurate height matters because the equation adds 6.25 times height, so even small entry mistakes can shift the result.
- 5Click Calculate to view your estimated BMR in kcal per day. If you are planning intake, use the BMR as the baseline and apply an activity multiplier with a TDEE calculator instead of treating BMR as your final daily target.
How It Works
Formula
Male: BMR = 10W + 6.25H - 5A + 5
Female: BMR = 10W + 6.25H - 5A - 161In the formula, W is weight in kilograms, H is height in centimeters, and A is age in years. The calculator multiplies weight by 10, multiplies height by 6.25, subtracts 5 times age, and then applies the sex-specific constant of +5 for male inputs or -161 for female inputs. After that, it rounds the raw result to the nearest whole kcal per day for display. The method estimates resting energy needs for adults from population data, so it is best used as a practical planning estimate rather than a direct measurement of personal metabolism. It tells you the calories your body may use at rest before daily activity, workouts, and digestion increase total energy expenditure.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Example 1: Female, 32 years old, 68 kg, 165 cm
Calculate each part first. Weight contributes 10 × 68 = 680, height contributes 6.25 × 165 = 1,031.25, and age subtracts 5 × 32 = 160. Then 680 + 1,031.25 - 160 - 161 = 1,390.25, which rounds to 1,390 kcal per day. This means the formula estimates about 1,390 calories per day at complete rest before any activity is added.
Example 2: Male, 40 years old, 82 kg, 180 cm
For this input, weight contributes 820 and height contributes 1,125. Age subtracts 200. Then 820 + 1,125 - 200 + 5 = 1,750 exactly. A result like this gives a useful rest-only baseline before you estimate maintenance calories from work, walking, training, and other daily movement.
Example 3: Male, 25 years old, 70 kg, 175 cm
The formula gives 10 × 70 = 700 for weight, 6.25 × 175 = 1,093.75 for height, and 5 × 25 = 125 for age. Add the male constant after subtracting age, so 700 + 1,093.75 - 125 + 5 = 1,673.75. The calculator rounds that to 1,674 kcal per day. The decimal shows why two people with similar body size can still land on slightly different whole-number results after rounding.
Example 4: Female, 55 years old, 90 kg, 160 cm
Weight contributes 900 and height contributes 1,000. Age subtracts 275. Then 900 + 1,000 - 275 - 161 = 1,464. Even with a higher body weight, the older age and shorter height keep the resting estimate lower than many people expect. That is one reason BMR should be checked with the full equation instead of guessed from weight alone.
Example 5: Female, 45 years old, 75 kg, 170 cm
Start with 10 × 75 = 750 for weight and 6.25 × 170 = 1,062.5 for height. Subtract 5 × 45 = 225 for age, then subtract the female constant of 161. The raw result is 750 + 1,062.5 - 225 - 161 = 1,426.5, which rounds to 1,427 kcal per day. This is a good reminder that half-calorie decimals are rounded to the nearest whole number in the displayed result.
Example 6: Marcus, 52, checks his rest baseline before a walking plan
Marcus wants a resting number before he adds daily walks and adjusts his meals. Weight contributes 10 × 96 = 960, height contributes 6.25 × 183 = 1,143.75, and age subtracts 5 × 52 = 260. Then 960 + 1,143.75 - 260 + 5 = 1,848.75, which rounds to 1,849 kcal per day. His maintenance intake will sit above that once activity is included, so the useful next step is a TDEE estimate, not eating 1,849 calories.
Four BMR equations for the same person
The same two adults run through the four prediction equations most calculators offer. This tool uses Mifflin-St Jeor. Katch-McArdle needs a body-fat percentage, so those rows assume 20% for the man and 28% for the woman.
| Equation | Person | Estimated BMR | Versus Mifflin-St Jeor |
|---|---|---|---|
| Mifflin-St Jeor (1990) | Male, 30 years, 80 kg, 178 cm | 1,768 kcal/day | Reference |
| Harris-Benedict, original (1919) | Male, 30 years, 80 kg, 178 cm | 1,855 kcal/day | +87 kcal |
| Harris-Benedict, revised (1984) | Male, 30 years, 80 kg, 178 cm | 1,844 kcal/day | +76 kcal |
| Katch-McArdle (20% body fat) | Male, 30 years, 80 kg, 178 cm | 1,752 kcal/day | -16 kcal |
| Mifflin-St Jeor (1990) | Female, 30 years, 65 kg, 165 cm | 1,370 kcal/day | Reference |
| Harris-Benedict, original (1919) | Female, 30 years, 65 kg, 165 cm | 1,442 kcal/day | +72 kcal |
| Harris-Benedict, revised (1984) | Female, 30 years, 65 kg, 165 cm | 1,430 kcal/day | +60 kcal |
| Katch-McArdle (28% body fat) | Female, 30 years, 65 kg, 165 cm | 1,381 kcal/day | +11 kcal |
Computed with each published equation and rounded to the nearest kcal. Sources: Mifflin et al., 1990, American Journal of Clinical Nutrition. Harris and Benedict, 1919, A Biometric Study of Basal Metabolism in Man, Carnegie Institution of Washington. Roza and Shizgal, 1984, American Journal of Clinical Nutrition. Katch-McArdle uses BMR = 370 + 21.6 x lean body mass in kg, as given in McArdle, Katch, and Katch, Exercise Physiology.
How to use a BMR estimate
A BMR result is most useful as a starting number. It estimates the energy your body may use if you stayed at complete rest for a full day. Real life adds walking, standing, training, chores, work, digestion, stress, sleep disruption, and recovery demands. That is why maintenance calories are usually higher than BMR and why many people pair this tool with a TDEE calculator next.
BMR also helps explain why two people of the same age can have different calorie needs. Height and weight move the equation in different directions, and the sex-specific constant shifts the estimate further. Someone taller or heavier usually has a higher resting estimate because more body tissue needs energy to function. Age pulls the estimate down over time because the formula subtracts calories for each year.
Many articles use BMR and RMR almost interchangeably, but the terms are not perfectly identical. Basal metabolic rate is the strict lab-style rest concept, while resting metabolic rate is often measured under less controlled conditions. In everyday nutrition planning, the numbers are often close enough that people use them in the same conversation. This calculator is specifically giving you a BMR-style estimate from a prediction equation, not a lab measurement.
The smartest way to use the output is to compare it with other context rather than treat it as a final answer. If your calculated BMR is 1,390 kcal per day, eating exactly 1,390 calories would usually mean less than full daily needs because normal life includes movement. If the result looks very different from your lived experience, review your inputs first and then consider factors the formula cannot see, such as muscle mass, medication, illness, or recent major changes in body weight.
Common mistakes
- Treating BMR as the same thing as maintenance calories. BMR is only the resting baseline, so daily needs are usually higher once activity is included.
- Entering weight in pounds or height in feet without converting to kilograms and centimeters first. The formula in this tool expects metric units only.
- Using old body measurements from months ago. A small change in weight or height entry can shift the estimate enough to matter for planning.
- Assuming the result proves you have a fast or slow metabolism. A formula estimate cannot diagnose metabolic issues or replace medical testing.
- Building a diet plan from BMR alone without considering activity level, training load, body-composition goals, or professional guidance when health issues are involved.
Limitations
This estimate assumes adult inputs and the population averages built into the Mifflin-St Jeor equation, which Mifflin et al. (1990, American Journal of Clinical Nutrition) derived from a sample of healthy adults rather than from people with illness, pregnancy, or unusual body composition. A systematic review by Frankenfield et al. (2005, Journal of the American Dietetic Association) found Mifflin-St Jeor was the most reliable of the common prediction equations for healthy nonobese and obese adults, yet it still missed the measured value by more than 10% for a meaningful share of people, and the review named indirect calorimetry as the reference method when accuracy matters. The formula cannot see thyroid disorders, fever, medication effects, metabolic adaptation after long dieting, or the calorie cost of healing from illness or injury, and it excludes activity, exercise, and digestion, so it is not a full daily calorie estimate by itself. Use this tool as a planning starting point, not as proof of your exact personal metabolism.
Embed this calculator on your site
Paste this code where you want the calculator to appear. It is responsive, mobile-friendly, resizes automatically, and is free to use as long as the credit line stays in place.
<script src="https://calctide.com/embed.js" data-tool="bmr-calculator" async></script>
<p style="font-size:12px;margin:4px 0 0">BMR Calculator by <a href="https://calctide.com/health/bmr-calculator/">CalcTide</a></p>Preview the embed at /embed/bmr-calculator/.