Metabolic Rate Calculator

Metabolic Rate Calculator

How to Use Metabolic Rate Calculator

1. Step 1: Enter details

   Add sex, age, height, and weight. Use your usual morning measurements when possible.

2. Step 2: Select units

   Choose Metric or US units. The calculator converts values automatically.

3. Step 3: Pick activity

   Select the activity level that best matches a typical week.

4. Step 4: Optional body fat

   Enter body fat % to enable Katch–McArdle (lean‑mass based BMR).

5. Step 5: Review results

   See RMR, TDEE, and suggested calorie targets for weight goals.

Key Features

• Accurate RMR (Mifflin–St Jeor)
• Optional BMR via Katch–McArdle
• Activity‑based TDEE output
• Calorie targets for goals
• Metric and US units
• Mobile‑friendly, privacy‑first

Understanding Results

Formula

This tool estimates resting energy with the Mifflin–St Jeor equation. It takes your weight (kg) × 10, height (cm) × 6.25, subtracts age (years) × 5, and then adds +5 for males or −161 for females. The result is your Resting Metabolic Rate (RMR) in kcal/day. If you provide body fat percentage, it also estimates Basal Metabolic Rate (BMR) using Katch–McArdle: 370 + 21.6 × lean mass (kg). Lean mass is your body weight minus fat mass.

Reference Ranges & Interpretation

RMR and BMR scale with body size, age, and sex. Taller and heavier bodies typically have higher resting needs. Daily energy (TDEE) multiplies your resting estimate by an activity factor to reflect movement and training. Use “Maintain” as a starting point. For weight loss or gain, a moderate change of ~10–20% usually balances progress with comfort. Expect normal day‑to‑day fluctuations in scale weight due to water, glycogen, and digestion.

Assumptions & Limitations

Equations reflect averages, not medical advice. Real‑world needs vary with genetics, non‑exercise activity, sleep, stress, climate, and health conditions. If you see a mismatch for several weeks, reassess your activity level and measurements, and consider consulting a registered dietitian or healthcare professional.

Complete Guide: Metabolic Rate Calculator

Use our metabolic rate calculator to estimate BMR/RMR and TDEE from age, sex, height, weight, and activity. Get targets for weight loss, gain, or maintenance.

This metabolic rate calculator estimates your resting energy needs and scales them to everyday life. It is designed to be simple on mobile, transparent about formulas, and practical for planning meals or training.

What is metabolic rate?

Your metabolic rate is the energy your body uses to stay alive and to move through the day. Even when you sit quietly, your body burns calories to run essential systems—breathing, circulation, temperature control, and cellular maintenance. That baseline cost is often described as resting energy (RMR) or basal needs (BMR). When we add movement, posture, fidgeting, and formal exercise, we reach your total daily energy expenditure—TDEE.

The metabolic rate calculator helps you quantify these pieces using established formulas and your personal inputs. With realistic activity levels, it converts a resting estimate into an everyday calorie target you can use for planning meals or adjusting body weight at a comfortable pace.

Metabolic rate changes across the lifespan. Children and adolescents generally have high energy needs relative to size as they grow. In adulthood, energy expenditure is shaped by body size, muscle mass, and activity. With age, average resting needs tend to decline slowly, in part because many people lose lean mass and move less. The good news is that resistance training, adequate protein, and regular daily movement can preserve muscle and keep your total energy needs higher than they would otherwise be.

BMR vs RMR vs TDEE

BMR (Basal Metabolic Rate) and RMR (Resting Metabolic Rate) are closely related. In practice, RMR measurements are slightly less strict than BMR measurements, but many equations people use—like Mifflin–St Jeor—are presented as resting estimates. Our tool computes RMR using Mifflin–St Jeor based on sex, age, height, and weight. When you provide body fat percentage, it also estimates BMR using Katch–McArdle, which is anchored to lean body mass.

TDEE takes your resting estimate and multiplies it by an activity factor that reflects your typical day. The result approximates what you burn on average. If you want a tool focused on one concept at a time, try the dedicated BMR calculator, RMR calculator, or TDEE calculator.

One helpful way to think about TDEE is to break it into parts. Your resting energy (RMR/BMR) is the largest slice. Non‑exercise activity (walking, posture, chores, fidgeting) can vary a lot between people and days. Structured exercise adds a smaller but important slice. The thermic effect of food—energy used to digest and process meals—usually sits around 8–10% of total intake for mixed diets. Improving any slice, even a little, can shift the whole picture over time.

How the metabolic rate calculator works

The calculator first estimates your resting needs with the Mifflin–St Jeor equation. It adds 10 × weight (kg), 6.25 × height (cm), subtracts 5 × age (years), and then uses a small constant that depends on sex: +5 for males, −161 for females. The result is your estimated RMR in kcal/day. It then multiplies that value by your selected activity factor to approximate TDEE.

If you add body fat percentage, we also estimate BMR using the Katch–McArdle equation: 370 + 21.6 × lean mass (kg). Lean mass is your body weight minus estimated fat mass. For many people, Katch–McArdle is more responsive to body composition changes than body weight alone. In the results, TDEE automatically switches to the method with body fat if you provide it; otherwise, it uses Mifflin–St Jeor.

Outputs include maintain calories and simple targets to reduce or increase intake by about 10–20%. Those ranges are widely used starting points. If you prefer fixed deficits, our calorie calculator and maintenance calorie calculator provide additional views of the same ideas.

Units are flexible. Choose centimeters and kilograms, or feet/inches and pounds—results are identical after conversion. If you are between sizes or seeing round numbers, it is fine to estimate to the nearest whole number. The tool is meant for everyday use; you can refine inputs later as needed.

Choosing your activity level

Activity multipliers convert a resting estimate into a realistic daily number. “Sedentary” fits desk‑based days with minimal walking. “Lightly active” covers a few weekly sessions of light exercise, while “Moderately active” matches consistent training 3–5 days per week. “Very active” is for near‑daily training, and “Extra active” applies to physically demanding jobs or long endurance sessions.

When unsure, choose the lower level and observe results for two to three weeks. Compare your predicted maintain calories to what actually holds your weight steady. Small adjustments are normal—people vary in non‑exercise activity (fidgeting, posture, walking) and in the way bodies adapt to training loads.

If you wear a fitness tracker, you might see daily numbers swing widely. That is normal. These devices are better at counting steps than estimating calories. Use them to nudge activity up, not to micromanage intake. Your trend over weeks—the scale, performance, and how you feel—matters more than any single day.

Why body composition matters

Two people can weigh the same but have different proportions of muscle and fat. Muscle tissue generally uses more energy at rest than fat tissue, so estimating lean mass can slightly change BMR predictions. That is why the Katch–McArdle equation ties directly to lean mass. If you don’t know your body fat percentage, you can still use the calculator—Mifflin–St Jeor remains one of the most accurate population equations available.

Want to estimate lean mass first? Try our body fat percentage calculator and lean body mass calculator. You can enter those values here to see how they affect your metabolic rate and TDEE.

Genetics, hormones, and sleep patterns also shape body composition. While you cannot control everything, you can influence many levers: train major muscle groups 2–3 times per week, aim for adequate protein spread across meals, and get consistent sleep. These habits support higher lean mass and more stable energy needs.

Metabolism and weight change

Body weight trends reflect the long‑term relationship between calories eaten and calories used. If your intake is below your expenditure for a while, weight tends to go down; if it’s above, weight tends to go up. Day‑to‑day noise is normal—water, glycogen, and digestion cause fluctuations that obscure the trend. Use your maintain estimate as a baseline, then consider a gradual change of 10–20% as a practical range for most adults.

If your goal is weight loss, you might target a 10% reduction and assess progress after two to four weeks. If needed, tighten to 15–20% with care for hunger, energy, and training quality. For step‑by‑step planning, our calorie deficit calculator and daily calorie calculator offer targeted views.

Progress is rarely linear. A weekly average is more meaningful than a single weigh‑in. Many people weigh a little more after salty meals, travel, or hard workouts. Rather than reacting day by day, take a calm look at 2–4 weeks of data before changing your plan. If you are losing faster than expected and feel low energy, loosen the deficit. If you have stalled for several weeks, tighten by a small amount or add a bit of movement.

Protein, macros, and the thermic effect of food (TEF)

Not all calories feel the same. Protein has a higher thermic effect—your body spends more energy digesting it—than carbs or fat. That’s one reason higher‑protein diets can feel more satisfying when you’re reducing calories. Many people do well with balanced macro ranges that emphasize protein and fiber while leaving room for preference and culture.

If you want macro targets from a calorie number, use our macro calculator or compute daily protein with the protein calculator. You can then return to this metabolic rate calculator to confirm calories and adjust activity or training as needed.

A practical approach is to set a protein range first—often around 0.7–1.0 grams per pound of goal body weight for active adults—then fill the remaining calories with carbs and fats in a way that supports performance and enjoyment. During higher‑intensity training phases, people often shift more calories to carbohydrates. During lower‑intensity or rest periods, fat can make up a larger share without issue.

Common metabolism myths and realities

“My metabolism is broken” is a common feeling when progress stalls. In most cases, measured metabolic rates fall within expected ranges once we account for body size, activity, and adherence to the plan. Adaptive changes are real—your body may unconsciously move less at lower intakes—but they are usually modest and can be managed by adjusting targets and staying consistent.

Another myth is that a single “fat‑burning food” or supplement dramatically raises metabolism. The thermic effect of food varies by macronutrient, not by marketing claims, and the overall impact is small compared with the basics: total calories, protein intake, physical activity, and sleep. Caffeine and cold exposure can nudge expenditure temporarily, but not enough to replace foundational habits.

Finally, metabolism does not crash from one light day of eating, nor does it skyrocket after a single big meal. The body is adaptable, but most meaningful shifts accumulate over weeks and months. Focus on the day‑to‑day actions you can repeat comfortably. Small, sustainable choices compound.

Examples and walk‑throughs

Imagine a 35‑year‑old female, 165 cm, 68 kg. Mifflin–St Jeor estimates an RMR around 1450 kcal/day. If she selects “Moderately active” (factor ≈ 1.55), her maintain calories land near 2250 kcal/day. A 10% reduction would target about 2025 kcal/day; 20% would be around 1800 kcal/day. If she knows her body fat is 28%, Katch–McArdle may estimate a similar or slightly different BMR depending on lean mass, thereby nudging her TDEE.

Consider a 40‑year‑old male, 178 cm, 82 kg, lightly active. RMR might land near 1700 kcal/day, and maintain calories near 2340 kcal/day. If he wants to build muscle slowly, a 10% surplus—about 2570 kcal/day—could be a comfortable starting point while focusing on training quality, sleep, and sufficient protein.

These examples illustrate how the same framework adapts to different goals. Start with the maintain estimate, choose a small change, and observe the trend over a few weeks. Adjust in small steps if progress stalls—consistency beats perfection.

If you prefer more structure, try setting weekly check‑ins. Note average weight, training performance, appetite, and sleep. If two out of four indicators worsen, you may be pushing too hard. Nudge calories up slightly, add a rest day, or trade a hard session for an easy walk. When indicators improve and progress continues, you have likely found a sustainable lane.

Limitations and next steps

Equations estimate averages—they are not medical advice, and they cannot account for every health condition. Hormonal changes, some medications, recovery from illness, and large shifts in training can alter energy use. If your results differ from expectations for several weeks, measure your intake more carefully, reassess activity, and consider seeking guidance from a registered dietitian or healthcare professional.

People with medical conditions that affect metabolism—such as thyroid disorders, diabetes, or chronic inflammatory diseases—should work with their care team on a personalized plan. Similarly, during pregnancy and postpartum, standard calorie equations do not apply in the same way. In those cases, discuss targets with a clinician who knows your history.

When you want more targeted tools, explore our focused calculators: the BMR calculator, RMR calculator, TDEE calculator, and maintenance calorie calculator. Use them together with this metabolic rate calculator to check your plan from multiple angles.

Simple, consistent habits—reasonable calories, enough protein, regular movement, quality sleep—do most of the heavy lifting for health and body composition. Tools like this make those habits easier to size and adjust over time.

Frequently Asked Questions