BMR Calculator
Calculate your basal metabolic rate with the Mifflin-St Jeor equation. Get your TDEE across five activity levels, calorie targets for your goal, and a macro breakdown.
Your Details
What you get
BMR
Calories your body burns at complete rest, just to maintain organ function.
TDEE Table
Total daily calorie needs across all five activity levels so you can see the full range.
Goal Calories and Macros
Calorie target for weight loss, maintenance, or muscle gain plus a macro breakdown.
TDEE by Activity Level
Calorie Target by Goal
Not medical advice. This calculator gives a general estimate based on the values you enter. It cannot account for your medical history, medication or body composition. Talk to a doctor or a registered dietitian before acting on any result.
How this BMR calculator estimates the calories your body burns before you move a muscle
Basal Metabolic Rate is the energy your body spends keeping you alive at complete rest, no food digesting, no exercise, just the furnace running to keep your heart beating, lungs breathing, and cells repairing themselves. It typically accounts for 60 to 75 percent of total daily energy use in a sedentary adult, which is why it’s the anchor number every calorie or diet plan starts from. This tool estimates it with an equation, since measuring it directly requires a lab and a metabolic cart.
The calculation runs entirely in your browser using plain arithmetic. Nothing about your age, weight, or sex is sent anywhere or stored once you close the page.
Two formulas, one toggle
The tool gives you a choice between two well known regression equations, both built by fitting resting energy expenditure measurements from real subjects to weight, height, age, and sex.
Notice the male and female equations differ by a flat offset in Mifflin-St Jeor, plus 5 versus minus 161, a 166 kcal gap that reflects the average difference in lean body mass between sexes at a given weight and height, since muscle tissue burns more energy at rest than fat tissue does. Harris-Benedict encodes the same idea with different coefficients on every term instead of one flat offset.
Turning BMR into a real calorie target
BMR alone isn’t a number you eat to, it’s a baseline. The tool multiplies it by an activity factor to estimate Total Daily Energy Expenditure, then layers a goal adjustment on top.
| Activity Level | Multiplier | Typical Pattern |
|---|---|---|
| Sedentary | x 1.2 | Desk job, little to no exercise |
| Lightly Active | x 1.375 | Light exercise 1 to 3 days a week |
| Moderately Active | x 1.55 | Moderate exercise 3 to 5 days a week |
| Very Active | x 1.725 | Hard exercise 6 to 7 days a week |
| Extremely Active | x 1.9 | Physical job plus daily training |
These multipliers trace back to the same activity factor system used alongside the original Harris-Benedict equation and later refined in dietetic practice guides, they’re a rough classification, not a personalized measurement, since actual daily movement varies enormously even within one label.
Goals and the macro split behind each one
Once TDEE is calculated, the tool offers five calorie targets built from it, plus a macro breakdown tuned to each goal.
Calorie deltas
Lose Fast subtracts 1000 kcal a day, Lose subtracts 500, Maintain holds TDEE, Gain adds 300, and Bulk adds 500. A 500 kcal daily deficit or surplus corresponds to roughly one pound of body weight change per week, since a pound of fat stores about 3500 kcal, a rule of thumb that’s approximate but widely used for planning.
Macro ratios by goal
Aggressive cuts lean protein-heavy at 40 percent to protect muscle during a deficit. Maintenance and bulking phases shift more calories toward carbohydrate, up to 50 percent on the Bulk preset, to fuel training volume. Every split allocates protein at 4 kcal per gram, carbs at 4 kcal per gram, and fat at 9 kcal per gram, the standard Atwater energy conversion factors.
Where estimates like this go wrong
Population fitted equations carry a margin of error of roughly plus or minus 10 percent even in the studies that validated them. That’s normal and expected, use the number as a starting point, track actual weight change over two to three weeks, and adjust the calorie target from there rather than treating the formula’s output as exact.
- Mifflin, St Jeor et al., American Journal of Clinical Nutrition, 1990, the original derivation study.
- Roza & Shizgal, American Journal of Clinical Nutrition, 1984, the revised Harris-Benedict coefficients used here.
- Academy of Nutrition and Dietetics guidance recommending Mifflin-St Jeor as the preferred predictive equation.
- Institute of Medicine, Dietary Reference Intakes for Energy covers the physiological basis of energy expenditure components.
This calculator gives an educational estimate, not a clinical measurement of your metabolism. It cannot detect thyroid disorders, metabolic adaptation, or other conditions that shift real energy needs. Talk to a doctor or registered dietitian before using it to guide a medical or significant dietary decision.
What people do with a BMR number
Setting a starting calorie target for a fat loss or muscle gain phase, sanity checking a fitness app’s default numbers, planning meal prep around a known daily calorie and macro budget, and giving a coach or dietitian a baseline figure to refine with real progress data instead of starting from a guess.
Questions About the BMR Calculator
BMR is the number of calories your body burns at complete rest to keep basic functions running — breathing, circulation, cell repair. It is the foundation of your calorie budget. Eat less than your TDEE to lose weight; eat more to gain. You cannot change your goal without knowing this number first.
Mifflin-St Jeor is a formula developed in 1990 that uses weight, height, age, and sex to estimate BMR. Research consistently finds it more accurate than older formulas like Harris-Benedict for most modern adults. The American Dietetic Association recommends it as the preferred formula for clinical use.
TDEE stands for Total Daily Energy Expenditure. It is your BMR multiplied by an activity factor that accounts for exercise and movement. This is the number of calories you actually burn each day. Eating at TDEE maintains your weight. A deficit below TDEE leads to weight loss; a surplus leads to gain.
A deficit of 500 kcal/day below TDEE results in roughly 0.5 kg of fat loss per week. A 1000 kcal/day deficit targets about 1 kg/week. However, most guidelines recommend not going below 1200 kcal/day for women or 1500 kcal/day for men without medical supervision, as this risks nutrient deficiencies and muscle loss.
Sedentary suits a desk job with minimal movement. Lightly active fits 1-3 days of light exercise. Moderately active fits 3-5 days of moderate gym or cardio work. Very active fits 6-7 hard training days. Extremely active fits athletes with twice-daily training or physically demanding jobs. Most people overestimate their level — if in doubt, go one lower.
The Mifflin-St Jeor formula predicts measured BMR within roughly 10% for most people. It is less accurate for those who are very muscular, very obese, or elderly. The formula treats people with the same height, weight, age, and sex as equivalent — it cannot account for differences in muscle mass or metabolic health. Use the result as a starting point, then adjust based on real-world weight change over 2-4 weeks.
Macros are protein, fat, and carbohydrate — the three calorie-containing nutrients. Protein (4 kcal/g) supports muscle retention and satiety. Fat (9 kcal/g) supports hormones and fat-soluble vitamins. Carbs (4 kcal/g) fuel training and brain function. The calculator suggests higher protein splits for weight loss goals and higher carb splits for muscle gain — both to support performance and body composition.
From the blog
The research behind the numbers
Where these formulas came from and what the studies actually showed.
