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Active Young Male
A 30-year-old male with moderate exercise routine, metric units.
Key values: 80 kg, 180 cm · Age 30 · Moderately active
Sedentary Office Worker
A 40-year-old female with a desk job, looking to understand her calorie needs.
Key values: 65 kg, 165 cm · Age 40 · Sedentary
Imperial Units Example
A 25-year-old male using imperial measurements with high activity level.
Key values: 176 lb, 5'11" · Age 25 · Very active
Documentation Contents
Understanding BMR and TDEE
Learn what BMR and TDEE mean, and how the calculator turns your inputs into daily calorie targets.
What is BMR?
Basal Metabolic Rate (BMR) represents the minimum number of calories your body needs to perform its most basic, life-sustaining functions while at complete rest. Think of it as the energy required for breathing, circulation, cell production, and maintaining body temperature – essentially, the energy needed just to stay alive if you were inactive all day.
What is TDEE?
Total Daily Energy Expenditure (TDEE) builds upon your BMR by adding the calories burned through physical activity and digestion. It represents the total number of calories you burn in a typical day. Knowing your TDEE helps estimate the daily calorie intake needed to maintain your current weight. TDEE is calculated by multiplying your BMR by an activity factor.
Activity Level Multipliers
- Sedentary (1.2): Little to no exercise (e.g., desk job).
- Lightly Active (1.375): Light exercise/sports 1-3 days/week.
- Moderately Active (1.55): Moderate exercise/sports 3-5 days/week.
- Very Active (1.725): Hard exercise/sports 6-7 days a week.
- Extremely Active (1.9): Very hard exercise, physical job, or training twice daily.
Inputs Glossary
A quick reference for each field and how it affects the results.
| Input | What to Enter | Why It Matters |
|---|---|---|
| Measurement System | Metric (kg, cm) or Imperial (lb, ft/in) | Controls which unit fields appear; values are converted to kg/cm internally. |
| Gender | Male or female | Used in formula constants that account for typical body composition differences. |
| Age | Years (0-120) | All formulas use age; Schofield uses age bands. |
| Weight | kg or lb | Primary driver of metabolic rate calculations. |
| Height | cm or ft/in | Used with weight and age; imperial inputs are combined into total inches for conversion. |
| Body Fat % | 0-100% (optional) | Required only for Katch-McArdle to estimate lean body mass. |
| BMR Formula | Mifflin-St Jeor, Harris-Benedict, Katch-McArdle, Schofield | Choose the equation that best fits your data and goals. |
| Activity Level | Sedentary to Extremely Active | Sets the multiplier used to estimate TDEE. |
How to Use the Calculator
Instructions for using the BMR calculator effectively
Input Parameters
- Measurement System: Choose metric (kg, cm) or imperial (lb, ft/in).
- Gender: Select male or female; formulas use different constants.
- Age: Enter your age in years (0-120).
- Weight: Enter your current weight in kg or lb.
- Height: Enter your height in cm or ft/in.
- Body Fat % (optional): Required only for Katch-McArdle to estimate lean body mass.
- BMR Formula: Choose the equation you want to use (Mifflin-St Jeor is the default).
- Activity Level: Select your typical daily activity level to estimate TDEE.
Steps to Follow
- Choose your measurement system and enter your age, gender, weight, and height.
- If you select Katch-McArdle, add your body fat percentage.
- Select the BMR formula and activity level that best match you.
- Click "Calculate" to generate your BMR, TDEE, and calorie goals.
- Adjust inputs and recalculate as your stats or activity change.
Calculation Methods
What the calculator does with your inputs.
BMR Formulas
Inputs are converted to metric units (kg, cm) before applying the formula you select. Each equation estimates resting energy based on weight, height, age, and in some cases body fat percentage.
Mifflin-St Jeor (Recommended)
Modern formula (1990) with strong accuracy for most adults.
Men:
Women:
Harris-Benedict (Revised)
Classic formula revised in 1984. Useful for comparison with older studies.
Men:
Women:
Katch-McArdle
Uses lean body mass for higher accuracy when body fat is known.
Schofield
Age- and sex-specific equations commonly used for children, adolescents, and some adult populations. The calculator shows the exact equation for your age in the Formula Used card.
TDEE and Activity Factor
Total Daily Energy Expenditure is estimated by multiplying your BMR by the activity multiplier you select.
Interpreting Your Results
How to understand and apply your BMR and TDEE results
What You Will See
- Basal Metabolic Rate (BMR): Calories your body needs at complete rest, shown as calories per day.
- Total Daily Energy Expenditure (TDEE): Your BMR multiplied by the selected activity factor, with the multiplier displayed in the results card.
- Calorie Goals by Objective: A set of maintenance, mild loss, moderate loss, mild gain, and moderate gain targets derived from your TDEE.
- Formula Used: The exact equation the calculator applied for your inputs.
Results are rounded to whole calories. Use the targets as a starting point and adjust after 2-3 weeks based on actual weight or performance changes.
Calorie Goals
How the calculator turns TDEE into practical targets.
The calculator generates five targets based on your TDEE: maintenance, mild loss, moderate loss, mild gain, and moderate gain. Use them as starting points and adjust based on how your body responds.
| Goal | What It Means | Typical Use |
|---|---|---|
| Maintain | Calories roughly equal to TDEE. | Weight maintenance or body recomposition. |
| Mild Loss | Small deficit below TDEE. | Slow, sustainable fat loss with minimal performance impact. |
| Moderate Loss | Larger deficit below TDEE. | Faster fat loss if recovery, mood, and training remain stable. |
| Mild Gain | Small surplus above TDEE. | Lean muscle gain with tighter fat control. |
| Moderate Gain | Larger surplus above TDEE. | More aggressive mass building, usually with some fat gain. |
If you need macronutrient targets, use the Macro Calculator and apply your chosen calorie goal there.
Real-World Applications & Examples
Practical ways to use your BMR and TDEE with concrete numbers.
Example 1 — Office Worker Losing Weight
Maria, 35 years old, female, 68 kg, 165 cm, sedentary activity level.
- BMR (Mifflin-St Jeor): 10 × 68 + 6.25 × 165 − 5 × 35 − 161 = 1,376 kcal/day
- TDEE (sedentary × 1.2): 1,376 × 1.2 = 1,651 kcal/day
- Mild loss target (−15%): 1,651 × 0.85 ≈ 1,403 kcal/day
A daily deficit of roughly 248 calories below TDEE produces gradual, sustainable fat loss of about 0.25 kg per week without severe hunger.
Example 2 — Athlete Building Muscle
James, 28 years old, male, 82 kg, 181 cm, 12% body fat, very active (1.725).
- BMR (Katch-McArdle): LBM = 82 × 0.88 = 72.2 kg; 370 + 21.6 × 72.2 = 1,929 kcal/day
- TDEE (× 1.725): 1,929 × 1.725 = 3,327 kcal/day
- Mild gain target (+15%): 3,327 × 1.15 ≈ 3,826 kcal/day
A surplus of about 500 calories supports muscle protein synthesis while limiting unnecessary fat accumulation during a training block.
Example 3 — Senior Maintaining Weight
Helen, 68 years old, female, 62 kg, 158 cm, lightly active (1.375).
- BMR (Schofield ≥60 female): 9.082 × 62 + 658.5 = 1,222 kcal/day
- TDEE (× 1.375): 1,222 × 1.375 = 1,680 kcal/day
- Maintenance target: 1,680 kcal/day
Schofield is recommended for older adults; the age-specific constants better reflect the lower metabolic rate that typically accompanies reduced muscle mass after age 60.
Research Insights: Why BMR Varies
Key drivers behind metabolic rate differences.
Lean Mass Is the Biggest Driver
Muscle tissue burns more energy than fat tissue, so people with more lean mass typically have a higher BMR. This is why strength training can raise energy needs over time.
Age and Hormones Matter
BMR tends to decline with age due to changes in muscle mass and hormonal shifts. The formulas include age and gender to account for these average trends, but individual variation can still be large.
Most research finds Mifflin-St Jeor predicts BMR within roughly 10% for many adults. That still leaves a wide range, so treat any formula as a starting point rather than a precise measurement.
Comparing BMR Equations
Different approaches to calculating BMR for various populations
Different BMR equations have been developed for various populations. Here's a brief comparison:
| Equation | Primary Population | Key Features | General Accuracy* |
|---|---|---|---|
| Mifflin-St Jeor | Adults | Uses weight, height, age, sex. Widely validated. | High (often within 10%) |
| Harris-Benedict (Revised) | Adults | Older formula, uses weight, height, age, sex. | Moderate (can overestimate) |
| Schofield | Children/Adolescents | Age-band equations; commonly used for younger populations. | Good (for pediatrics) |
| Katch-McArdle | Athletes/Known LBM | Uses Lean Body Mass (LBM) instead of total weight. | Very High (if LBM accurate) |
*Accuracy compared to indirect calorimetry (lab measurement). Mifflin-St Jeor generally shows better accuracy (lower error) than Harris-Benedict for most adults, especially those with obesity.
Frequently Asked Questions
Common questions about BMR, TDEE, and their calculations
Which formula should I choose?
Mifflin-St Jeor is a solid default for most adults. Choose Katch-McArdle if you have a reliable body fat percentage. Schofield is commonly used for children and adolescents. Harris-Benedict is useful for comparison with older references.
Why do different formulas give different results?
Each equation was built from different study populations and assumptions. Small differences are normal, so use the formula as a starting point and adjust based on real-world results.
Do I need body fat percentage?
Only if you choose Katch-McArdle. If you are unsure of your body fat percentage, use Mifflin-St Jeor or Harris-Benedict instead.
How accurate is the activity multiplier?
It is a helpful estimate but not exact. If your weight or performance is not moving as expected after a few weeks, adjust your intake and recalculate.
Should I eat below my BMR to lose weight?
It is generally not recommended for extended periods. Aim for a moderate deficit from TDEE so you can maintain energy, recovery, and nutrient intake.
How often should I recalculate?
Recalculate after meaningful changes in weight, activity, or body composition (around 5-10 lb is a common rule of thumb). Annual updates are usually enough if your stats stay stable.
When BMR Estimates Fall Short
Key limitations and advice regarding BMR calculations.
Accuracy of Estimates
- BMR and TDEE are estimates and can vary based on genetics, hormones, medications, and body composition.
- Katch-McArdle depends on body fat percentage, which is often hard to measure accurately.
- If you are pregnant, under 18, or managing a medical condition, consult a qualified professional before using calorie targets.
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