# BMR Calculator Estimate your basal metabolic rate (BMR) and daily calorie needs at rest based on your age, gender, height, and weight for accurate results. --- - **Canonical URL:** https://dothecalculation.com/calculators/bmr-calculator - **Category:** Health and fitness - **Publisher:** Do The Calculation (https://dothecalculation.com) - **Cost:** Free, no account or sign-up required - **Privacy:** Runs entirely in the browser; inputs are never sent to a server - **Methodology:** https://dothecalculation.com/methodology - **Reviewed by:** Dr. Sarah Jenkins, PhD, PhD in Exercise Physiology & Metabolism, Stanford University (https://dothecalculation.com/about/team/sarah-jenkins) --- ## Calculate your Basal Metabolic Rate Estimate the minimum energy your body requires to perform basic life-sustaining functions at complete rest. - Resting energy baseline - Predictive metabolic equations - Age and gender adjustments ## Basal Metabolism: The Body’s Baseline Energy Cost Before you take a single step, lift a weight, or digest a meal, your body is consuming energy. This foundational energy requirement is called your Basal Metabolic Rate (BMR). BMR represents the absolute minimum amount of energy (measured in calories) your body needs to maintain vital physiological processes while in a completely inactive, awake state, in a temperate environment, and in a post-absorptive state (fasted for 12 hours). Even when you are lying still, your body is working hard. Energy is consumed by cellular processes: maintaining the sodium-potassium pumps that regulate electrical gradients in your cells, synthesizing proteins, filtering waste through the kidneys, pumping blood through the circulatory system, and powering brain cell communications. Your internal organs are highly active: the liver and brain consume the largest share of basal energy (about 20% each), followed by skeletal muscle (18%), the heart (7%), and the kidneys (7%). The remaining balance is used by bone, skin, and adipose tissue. BMR accounts for the majority of your daily energy expenditure—typically 60% to 75% of your Total Daily Energy Expenditure (TDEE). Understanding this baseline is essential for nutrition and exercise planning. It represents the physiological floor; eating below your BMR for long periods signals metabolic starvation, triggering hormonal changes that slow your metabolism and degrade lean tissues. ## Mathematical Models of BMR Estimation Since measuring BMR directly requires indirect calorimetry (measuring oxygen consumption inside a metabolic chamber), researchers have developed predictive mathematical models. The calculator supports three of the most widely validated and utilized equations in clinical nutrition: **1. The Mifflin-St Jeor Equation**: This is the current clinical standard. Developed in 1990, it is based on modern body compositions and is accurate for most individuals. The formulas are: $$\text{Men: BMR} = 10 \times \text{Weight (kg)} + 6.25 \times \text{Height (cm)} - 5 \times \text{Age (years)} + 5$$ $$\text{Women: BMR} = 10 \times \text{Weight (kg)} + 6.25 \times \text{Height (cm)} - 5 \times \text{Age (years)} - 161$$ **2. The Revised Harris-Benedict Equation**: Originally formulated in 1918 and updated in 1984 by Roza and Shizgal, this equation remains highly popular, though it can overestimate needs in overweight individuals: $$\text{Men: BMR} = 88.362 + 13.397 \times \text{Weight (kg)} + 4.799 \times \text{Height (cm)} - 5.677 \times \text{Age (years)}$$ $$\text{Women: BMR} = 447.593 + 9.247 \times \text{Weight (kg)} + 3.098 \times \text{Height (cm)} - 4.330 \times \text{Age (years)}$$ **3. The Katch-McArdle Equation**: Unlike the other formulas, this equation does not factor in age, height, or sex. Instead, it relies entirely on Lean Body Mass (LBM). This makes it highly accurate for athletic populations with low body fat, but it requires an accurate body fat estimate: $$\text{BMR} = 370 + 21.6 \times \text{Lean Mass (kg)}$$ ## Step-by-Step BMR Walkthrough: Comparing Models To see how these formulas differ mathematically, let us run BMR estimates for the same individual: a 35-year-old female who weighs \(70\text{ kg}\), stands \(165\text{ cm}\) tall, and has a body fat percentage of 25% (meaning she has \(52.5\text{ kg}\) of lean mass). **Mifflin-St Jeor Calculation**: Step 1: Compute weight component: \(10 \times 70 = 700\). Step 2: Compute height component: \(6.25 \times 165 = 1,031.25\). Step 3: Compute age component: \(5 \times 35 = 175\). Step 4: Combine components and subtract 161 for female: \(700 + 1,031.25 - 175 - 161 = 1,395.25\). The Mifflin-St Jeor estimate is **1,395 calories/day**. **Revised Harris-Benedict Calculation**: Step 1: Compute weight component: \(9.247 \times 70 = 647.29\). Step 2: Compute height component: \(3.098 \times 165 = 511.17\). Step 3: Compute age component: \(4.330 \times 35 = 151.55\). Step 4: Add baseline constant: \(447.593 + 647.29 + 511.17 - 151.55 = 1,454.503\). The Revised Harris-Benedict estimate is **1,455 calories/day** (overestimating by 60 calories). **Katch-McArdle Calculation**: Step 1: Multiply lean mass (52.5 kg) by the multiplier (21.6): \(21.6 \times 52.5 = 1,134\). Step 2: Add the baseline constant: \(370 + 1,134 = 1,504\). The Katch-McArdle estimate is **1,504 calories/day**. Because this method accounts for her higher muscle mass directly, it indicates her actual baseline is higher than predicted by height-weight assumptions. ## Physiological Factors Regulating Basal Metabolic Rate Your BMR is not fixed; it is regulated by a combination of genetics, body composition, hormones, and environmental factors: **Fat-Free Mass (Muscle)**: This is the primary predictor of BMR. Muscle tissue requires significant energy to maintain even at rest, burning roughly three times as many calories per pound as fat tissue. Increasing muscle mass raises BMR permanently. **Thyroid Hormones**: Thyroxine (T4) and Triiodothyronine (T3), produced by the thyroid gland, act as the master regulators of cellular metabolism. High thyroid levels (hyperthyroidism) accelerate cellular activity, dramatically raising BMR, while low levels (hypothyroidism) cause metabolic rates to plummet. **Age**: BMR typically declines by 1% to 2% per decade after early adulthood. This is mostly driven by sarcopenia (age-related loss of muscle mass) rather than a direct cellular slowdown. Consistent strength training can prevent this decline. ## How to Use This Calculator Select your sex, activity level, and enter your age, height in centimeters, and weight in kilograms. The calculator applies the Mifflin-St Jeor equation to your inputs to compute BMR, then multiplies by your selected activity factor to estimate your TDEE (maintenance calories). ## Worked Example: 35-Year-Old Female, 165 cm, 68 kg Female, age 35, height 165 cm, weight 68 kg, light activity (factor 1.375). Mifflin-St Jeor: \(10 \times 68 + 6.25 \times 165 - 5 \times 35 - 161 = 680 + 1{,}031.25 - 175 - 161 = 1{,}375.25\) kcal/day BMR. Estimated TDEE at light activity: \(1{,}375.25 \times 1.375 \approx 1{,}891\) kcal/day — the maintenance-calorie estimate this person would use as a baseline before adjusting for a weight-loss or weight-gain goal. ## Related Calculators Feed this BMR into the [calorie calculator](/calculators/calorie-calculator) or [TDEE calculator](/calculators/tdee-calculator) for a full daily target, or compare it against your real-world numbers with the [adaptive TDEE calculator](/calculators/tdee-adaptive-calculator). ## Frequently asked questions ### What is Basal Metabolic Rate (BMR)? BMR is the baseline energy expenditure your body requires to maintain life-sustaining functions (organ activity, cellular pumps) while at complete rest and fasted. ### How does BMR differ from RMR? BMR requires strict fasting and rest conditions in a laboratory. Resting Metabolic Rate (RMR) is measured under less restrictive conditions, typically yielding slightly higher results (by 5-10%). ### Which BMR formula is the most accurate? The Mifflin-St Jeor formula is considered the most accurate for modern populations. The Katch-McArdle formula is preferred for athletic individuals with known body fat percentages. ### Can I increase my BMR? Yes. Building skeletal muscle tissue is the most effective way to permanently raise BMR, as muscle requires more resting metabolic maintenance than fat tissue. ### Does eating below my BMR slow my metabolism? Yes. Severe, prolonged caloric restriction below BMR triggers adaptive thermogenesis ("starvation mode"), slowing metabolic rates and signaling muscle breakdown. ### How is BMR calculated in metric units? Mifflin-St Jeor: Men BMR = (10 × kg) + (6.25 × cm) - (5 × age) + 5. Women BMR = (10 × kg) + (6.25 × cm) - (5 × age) - 161. ### Does body fat percentage affect BMR? Yes. Since fat is less metabolically active than muscle, two people of the same weight will have different BMRs if their body fat percentages differ. The Katch-McArdle formula accounts for this. ### Does genetics play a role in BMR? Yes. Genetic variables regulate baseline thyroid output, receptor sensitivity, and body frame size, which account for variations in metabolic rates among individuals. ### How does age affect my BMR? BMR naturally declines by 1-2% per decade after age 30, primarily due to sarcopenia (loss of muscle tissue). Strength training helps preserve muscle mass. ### Should I eat fewer calories than my BMR to lose weight? Generally no. To lose weight safely, set your caloric intake below your TDEE (maintenance level) but above your BMR to protect muscle mass and endocrine function. ## Related concepts - **Adaptive Thermogenesis** — The metabolic adaptation slowing BMR in response to prolonged caloric deficits. - **Lean Body Mass** — Total body weight minus fat mass, representing muscle, bone, and organ weight. - **Indirect Calorimetry** — The clinical standard for measuring BMR by tracking oxygen consumption and carbon dioxide output. ## Related guides - [BMR and Metabolic Rate: Understanding Your Basal Metabolism](https://dothecalculation.com/blog/health/bmr-metabolic-rate) — Understand what BMR really measures, how the Mifflin-St Jeor formula works, and how to use BMR and TDEE for practical calorie planning. - [TDEE Calculation Guide: Estimate Maintenance Calories](https://dothecalculation.com/blog/health/tdee-calculation-guide) — Learn how TDEE is estimated from BMR and activity, reproduce the calculator result, and validate maintenance calories with real-world trends. ## Related calculators - [Caloric Deficit & Timeline Planner](https://dothecalculation.com/calculators/caloric-deficit-bodyfat-calculator) — Estimate your projected weight loss timeline and adapted BMR using dynamic metabolic modeling based on your caloric deficit. - [Adaptive TDEE Calculator](https://dothecalculation.com/calculators/tdee-adaptive-calculator) — Calculate your true adaptive TDEE using real-world daily calorie intake and weight trend data for more accurate results. - [Calorie Calculator](https://dothecalculation.com/calculators/calorie-calculator) — Estimate your daily calorie needs for weight loss, maintenance, or muscle gain based on age, gender, height, weight, and activity level. - [TDEE Calculator](https://dothecalculation.com/calculators/tdee-calculator) — Estimate your Total Daily Energy Expenditure (TDEE) to determine how many calories you burn and need each day for your goals. - [Metabolic Age Calculator](https://dothecalculation.com/calculators/metabolic-age-calculator) — Estimate your metabolic age by comparing your basal metabolic rate (BMR) to population health benchmarks for your age group. - [Resting Metabolic Rate Calculator](https://dothecalculation.com/calculators/rmr-calculator) — Calculate the calories your body burns daily at complete rest using proven, science-based metabolic rate estimation models and formulas. --- _This calculator is for educational and fitness planning purposes only. BMI classifications, metabolic rates (BMR/TDEE), body fat percentages, caloric targets, and ideal weight estimations are clinical guidelines and do not replace personalized medical advice, diagnostic evaluations, or dietetic counseling. Always consult with a licensed physician or registered dietitian before starting a new diet or intense exercise program._ --- _Source: [Do The Calculation](https://dothecalculation.com/calculators/bmr-calculator). Quote freely with attribution and a link to this page._