BMR Calculator – Basal Metabolic Rate, TDEE & Calorie Goals
Calculate Your Basal Metabolic Rate
Basal Metabolic Rate (BMR) is an estimate of the energy your body needs to support essential physiological functions while at rest. This BMR Calculator uses established predictive equations to estimate resting energy expenditure from your age, sex, height and weight, with additional support for body-fat-based calculation through the Katch-McArdle equation.
- Mifflin-St Jeor BMR
- Revised Harris-Benedict BMR
- Katch-McArdle BMR
- Estimated maintenance calories (TDEE)
- Activity-level calorie requirements
- Smart calorie targets for cutting, maintaining or bulking
- Lean body mass
- Body-fat-based calculations
- Protein, carbohydrate and dietary-fat targets
- Estimated hydration needs
The result is a prediction, not a laboratory measurement of your metabolism. Predictive equations are useful because they make individualized estimates from ordinary measurements, but their accuracy varies between individuals and populations. The original Mifflin-St Jeor research, for example, developed a resting-energy expenditure equation using indirect calorimetry measurements from 498 healthy adults.
What Is BMR?
BMR stands for Basal Metabolic Rate. It represents the amount of energy your body would theoretically require to maintain fundamental physiological functions under basal resting conditions.
Your body continuously uses energy for processes such as breathing, circulation, maintaining body temperature, cellular activity, nervous-system function, and organ function. BMR is therefore only one part of your total daily energy expenditure.
TOTAL DAILY ENERGY USE
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BMR Activity & Food
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Resting energy ┌─────┼─────┐
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NEAT EAT TEFThis is why your BMR and your daily calorie requirement are not the same thing.
BMR vs. TDEE
One of the most common mistakes when using a BMR calculator is assuming that the BMR result represents the number of calories you should eat every day. It does not.
BMR (Basal Metabolic Rate)
Your BMR is a resting-energy estimate assuming zero movement or digestive processing.
TDEE (Total Daily Energy Expenditure)
Your Total Daily Energy Expenditure accounts for your daily activity, workouts, and digestion in addition to your resting expenditure. Explore complete daily expenditure modeling in our TDEE Calculator.
The calculator therefore lets you see how the same BMR translates into different calorie requirements under different activity assumptions. The use of BMR as the foundation for estimating total energy requirements is also reflected in the FAO/WHO/UNU framework for human energy requirements.
How This BMR Calculator Works
The calculator follows a straightforward sequence:
Step 1: Enter Your Personal Measurements
Enter age, biological sex, height, and body weight. The calculator supports multiple unit systems (US, Metric, Other) so you can work in the units most convenient for you.
Step 2: Choose a BMR Equation
You can select among several established predictive equations: Mifflin-St Jeor, Revised Harris-Benedict (1984), or Katch-McArdle.
Step 3: Select an Activity Level
The calculator converts estimated resting expenditure into a modeled maintenance calorie requirement using its 6-tier activity multipliers.
Step 4: Select a Goal
Choose from available goal modes: aggressive cut, slow cut, maintain, slow bulk, aggressive bulk, or performance. The calculator produces an estimated calorie target associated with that goal.
Step 5: Review Body Composition and Macronutrients
Where applicable, review lean body mass, fat mass, protein targets, carbohydrate targets, and dietary-fat targets. The result can then be exported via CSV, shared via URL, or saved locally.
Mifflin-St Jeor Equation
The calculator's primary BMR option is the Mifflin-St Jeor equation:
The equation was published in 1990 after being derived from data from 498 healthy adults whose resting energy expenditure was measured using indirect calorimetry.
Worked Reference Scenario
Suppose a male is 25 years old, weighs 160 lb (72.5748 kg), and is 70 inches (177.8 cm) tall:
That is the exact value represented by the supplied PDF's US-unit reference scenario.
Why Your BMR Can Change When You Switch Units
A mathematically important detail is that unit conversion can introduce displayed differences when the entered values are rounded.
For example: 160 lb is approximately 72.5748 kg. But entering 72.6 kg uses a slightly different number. Likewise, 70 inches = 177.8 cm, while manually entering 178 cm is not identical.
Because BMR equations use the actual numerical values, these small differences can produce a difference of one or two displayed calories. This explains why the reference PDF can show approximately 1,717 kcal, while a screenshot using explicitly entered 72.6 kg and 178 cm produces approximately 1,719 kcal. That is a rounding/input-state difference, not evidence that the equation itself has changed. The calculator therefore keeps greater numerical precision internally and rounds the final result for presentation.
Revised Harris-Benedict & Katch-McArdle Equations
Revised Harris-Benedict (1984)
Published by Roza and Shizgal in 1984 and evaluated against indirect calorimetry:
Because the coefficients differ from Mifflin-St Jeor, the two equations produce slightly different estimates for the same person. Different models reflect different baseline datasets and methodologies.
Katch-McArdle Equation
Calculates expenditure strictly from Lean Body Mass (LBM), making it independent of gender:
Example: Weight = 72.6 kg, Body fat = 17% → LBM = 60.26 kg → BMR ≈ 370 + (21.6 × 60.26) ≈ 1,672 kcal/day. Accurate body fat estimates from our Body Fat Calculator are critical here.
Which BMR Formula Should You Use & Why Calculators Differ
A strong general-purpose choice when you know age, sex, height, and weight.
Useful as an additional comparison using a distinct historical regression dataset.
Useful when you have a reasonably reliable estimate of body fat percentage or lean mass.
Why Different BMR Calculators Give Different Answers:
- Different equations: Mifflin-St Jeor and Harris-Benedict do not produce identical estimates.
- Different unit precision: 160 lb converted exactly to kg (72.5748 kg) differs from manually entering 72.6 kg.
- Different rounding: Some calculators round intermediate variables; others maintain full floating precision.
- Different definitions: Some sites report BMR while others report RMR (Resting Metabolic Rate) or immediately multiply by activity.
- Different activity models: Starting from the same BMR, different calculators apply different multipliers.
Understanding Activity Multipliers
Once BMR is estimated, the calculator shows maintenance calories across physical activity tiers:
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.20× | Little to no structured physical exercise; desk-bound lifestyle |
| Lightly Active | 1.375× | Light exercise or occupational walking 1–3 days/week |
| Moderately Active | 1.55× | Moderate exercise or sports training 3–5 days/week |
| Very Active | 1.725× | Hard exercise or demanding physical labor 6–7 days/week |
| Athlete / Intense | 1.90× | Intense training 6–7 days/week or twice-daily sports conditioning |
| Extra Active | 2.00× | Heavy physical job combined with intense athletic training |
These multipliers serve as estimation parameters, not laboratory measurements. If BMR = 1,700 kcal/day, then at 1.55×: 1,700 × 1.55 = 2,635 kcal/day modeled maintenance. Activity categories are approximate because people with the same nominal activity level can have very different step counts and occupations.
Weight Loss, Weight Gain, Lean Bulk & Body Composition
BMR and Weight Loss
Weight loss generally requires sustained energy intake below total expenditure (Calorie Intake < TDEE). For example, TDEE = 2,600 kcal and Intake = 2,100 kcal gives a modeled 500 kcal/day deficit. Long-term weight change is dynamic rather than linear, as modeled by the NIH/NIDDK Body Weight Planner. For daily deficit planning, compare with our Calorie Calculator.
BMR and Weight Gain
For weight gain, Calorie Intake > TDEE (e.g. TDEE = 2,600 kcal and Intake = 2,900 kcal gives a 300 kcal/day surplus). Actual changes depend on training, appetite, activity, and recovery. A calorie target is a planning starting point rather than a guarantee.
Lean Bulk Workflow
A lean bulk provides enough energy to support tissue growth while controlling excess fat accumulation: Estimate BMR → estimate TDEE → select a modest surplus → monitor results → adjust. To establish daily protein intake, utilize our Protein Calculator.
Body Composition & Lean Mass
Two people of identical body weight can have vastly different muscle, fat, bone, and water proportions. Lean body mass is estimated as LBM = Weight × (1 - BF). At 72.6 kg and 17% body fat, LBM is approximately 72.6 × 0.83 = 60.3 kg. Evaluate clinical stature with our BMI Calculator and Ideal Weight Calculator.
BMR and Macronutrients
The calculator's smart-goal system translates daily energy requirements into structured macronutrient targets using physiological caloric densities:
For example: 150 g of protein provides 150 × 4 = 600 kcal, while 70 g of fat provides 70 × 9 = 630 kcal. These conversions translate a calorie target into an approximate macronutrient distribution. To customize carbohydrate, fat, and protein ratios for specific training goals, explore our Macro Calculator.
Physiological Determinants: Age, Sex, Muscle & Direct Measurement
Why BMR Changes as You Lose Weight
Because body mass influences resting expenditure, weight loss lowers predicted BMR. Someone who preserves considerable lean mass retains a higher resting expenditure than someone with greater lean tissue loss. Re-evaluate your calorie targets after significant weight shifts.
BMR, Age & Sex
As age increases, equations predict lower resting expenditure due to gradual sarcopenia. For sex, Mifflin-St Jeor applies +5 for males and -161 for females, reflecting population-level differences in average skeletal muscle mass, bone density, and essential adipose tissue.
Does Muscle Increase BMR?
Muscle contributes to resting expenditure (~6 kcal/lb/day), but internal organs (liver, brain, heart, kidneys) have far higher resting energy demands relative to mass. Adding muscle elevates BMR, but the effect is part of an integrated physiological profile rather than an enormous automatic increase.
Can You Measure BMR Directly?
A calculator does not directly measure metabolism. A direct measurement requires laboratory indirect calorimetry (measuring O₂ consumption and CO₂ production under strict overnight fasting conditions). A predictive calculator generates a mathematical prediction from input parameters.
Real-world maintenance intake can differ because: activity category was selected incorrectly, daily movement (NEAT) differs from assumptions, body composition differs, exercise volume fluctuates, food tracking is inaccurate, or adaptive thermogenesis occurs during prolonged dieting. Use your calculation as a starting hypothesis and calibrate against your multi-week scale trend.
BMR Calculator Example From the Reference
The supplied reference PDF uses a 25-year-old male baseline:
| Input / Metric | Reference Value | Notes |
|---|---|---|
| Age & Gender | 25 years (Male) | Healthy adult baseline |
| Height | 178 cm (70 in = 177.8 cm) | Displayed rounded to 178 cm in report |
| Weight | 160 lb (72.5748 kg) | Displayed rounded to 72.6 kg in report |
| Estimated Body Fat | 17.1% | Deurenberg adult predictive formula |
| Selected BMR | 1,717 kcal/day | Mifflin-St Jeor: 10(72.5748) + 6.25(177.8) - 5(25) + 5 = 1,716.998 |
| Maintenance TDEE | 2,661 kcal/day | Moderately Active: 1,717 × 1.55 = 2,661.35 kcal/day |
| Lean Body Mass | 132.6 lb | 160 lb × (1 - 0.171) = 132.64 lb (FFMI: 19) |
| Water Intake Target | 3.2 L (14 cups) | Hydration estimate based on body weight + moderate activity |
Notice that the exact converted weight is approximately 72.5748 kg, whereas manually entering 72.6 kg creates a slightly different mathematical input (1,718.5 → 1,719 kcal). That explains the small differences seen across views.
How to Use the BMR Calculator Properly & Limitations
Recommended Workflow: Start with the Mifflin-St Jeor estimate using accurate height and weight → Compare formulas (Revised Harris-Benedict and Katch-McArdle) → Estimate maintenance using your typical activity level → Select your goal (cut, maintain, bulk, performance) → Validate against multi-week scale and performance reality → Recalculate when body weight changes significantly.
Calculator Limitations: A BMR calculator cannot directly observe oxygen consumption, carbon-dioxide production, spontaneous fidgeting, exact food intake, or daily endocrine fluctuations. FAO/WHO energy-requirement literature treats predictive equations as practical estimation tools rather than universal laboratory measurements.
Frequently Asked Questions
Scientific Interpretation Note
The most important point to remember is that BMR is a model output, not a biological constant. A calculator takes measurable characteristics such as age, sex, height and body weight and transforms them through a predictive equation. That gives you a useful estimate. It does not mean your metabolism has been measured to the nearest calorie. A difference of a few calories between two sites may simply reflect different input precision or equation selection, while a larger difference comes from using a different predictive model.
This calculator is provided for educational and planning purposes only. It estimates resting energy expenditure from predictive equations and does not directly measure metabolism or diagnose medical conditions. Individual energy requirements can differ substantially from calculator estimates. People who are pregnant or breastfeeding, have a medical condition, have a history of an eating disorder, are under 18, or have specialized clinical or athletic nutrition requirements should seek individualized guidance from an appropriately qualified healthcare professional.