BMR Calculator

Overview

How to use this calculator

1. Measure or look up your current weight in kilograms and height in centimeters; convert from pounds/inches if needed.
2. If you only have imperial units, convert carefully (1 lb ≈ 0.4536 kg; 1 in = 2.54 cm) so the equation uses the correct scale.
3. Enter your age in years and select the gender option that corresponds to the Mifflin‑St Jeor constants you want to use.
4. The calculator runs the appropriate version of the Mifflin‑St Jeor equation to estimate your BMR in calories per day.
5. Review the BMR result and think of it as your baseline daily energy use if you were completely at rest.
6. If you want a rough maintenance calorie estimate, multiply the BMR by an activity factor that matches your lifestyle (sedentary, lightly active, very active, etc.).
7. Use that maintenance estimate alongside your goals (weight loss, maintenance, gain) to decide whether to eat below, at, or above that level—and then adjust based on real‑world weight trends.
8. Recalculate periodically if your weight, activity level, or training phase changes so your baseline estimate stays current.

Inputs explained

Weight (kg)

Your body weight in kilograms. If you know your weight in pounds, divide by 2.20462 to convert to kilograms (for example, 165 lb ÷ 2.20462 ≈ 74.8 kg).

Height (cm)

Your height in centimeters. If you know your height in inches, multiply by 2.54 to convert (for example, 70 in × 2.54 ≈ 178 cm).

Age

Your age in years. BMR tends to decrease gradually with age as average lean mass and baseline energy expenditure decline.

Gender

Mifflin‑St Jeor uses different constants for males and females. Choose the option that best matches the equation you want to apply, or follow guidance from your coach or clinician if your situation is more nuanced.

Outputs explained

BMR (calories/day)

An estimate of how many calories your body burns at rest over 24 hours. This does not include planned exercise or day‑to‑day activity and is best used as a baseline for further calculations such as TDEE.

When to use it

• Setting initial calorie targets for weight loss, maintenance, or muscle gain by combining BMR with an activity multiplier.
• Establishing a baseline before choosing macro ratios or designing a nutrition plan for training blocks.
• Comparing how BMR estimates change over time as your weight, body composition, or age changes.
• Providing a starting point for conversations with a coach or dietitian about appropriate calorie ranges.
• Estimating how much to eat during a maintenance phase before a cut or bulk by using BMR as the baseline and then adjusting for activity.
• Creating a starting calorie target for a structured plan (like a meal prep schedule) and then refining based on weekly scale and performance data.
• Evaluating whether a reported calorie intake seems plausibly above or below maintenance when troubleshooting weight plateaus.
• Helping travelers or shift workers adjust intake when daily activity levels change drastically from their usual routine.
• Using a consistent baseline when logging nutrition data so changes in weight can be attributed to actual intake and activity rather than shifting assumptions.

Tips & cautions

• Use recent, accurate measurements and avoid guessing your weight or height if you want more reliable estimates.
• Treat BMR as a baseline, not a fixed truth—multiply by an activity factor to estimate maintenance, then adjust based on actual weight trends over several weeks.
• If you’re systematically gaining or losing weight at a rate that doesn’t match your planned calorie deficit or surplus, adjust your assumed maintenance calories rather than clinging to the formula.
• Remember that strength training and higher lean mass can increase resting energy expenditure; formulas can’t perfectly capture everyone’s unique metabolism.
• Avoid making extreme calorie cuts based solely on a BMR estimate. Sustainable changes, adequate protein, and sufficient energy for your training and health are more important than hitting an exact number.
• Weigh and measure consistently (same time of day, similar conditions) so changes in BMR estimates reflect real trends rather than measurement noise.
• If you track intake, look at weekly averages rather than daily swings; BMR is a long‑term baseline, not a day‑to‑day dial.
• Choose an activity factor that matches your true lifestyle, not your ideal routine. Overestimating activity is a common reason calorie targets feel “too high.”
• When dieting, your real energy expenditure can drop slightly due to reduced movement (NEAT) and metabolic adaptation; use trends to adjust.
• If you have a highly variable schedule (shift work, seasonal sports), calculate separate baselines for different activity phases.
• Estimates resting energy expenditure only; true daily needs (TDEE) depend on activity, body composition, genetics, hormone status, and health conditions.
• Not designed for children, pregnant or breastfeeding individuals, or clinical nutrition situations where specialized equations and supervision are required.
• Does not directly incorporate body fat percentage or lean body mass; other equations that use lean mass may be more appropriate for certain athletic or clinical populations.
• BMR formulas are population averages and can be off for individuals—some people run “hotter” or “cooler” metabolically than the equation predicts.
• Measurement error in weight, height, or age (or misclassification of gender in the equation) will directly affect the estimate.
• Short‑term dieting, illness, or recovery can temporarily shift energy expenditure, so a formula‑based estimate may drift during those periods.
• The equation reflects average adults; if you have significant metabolic or endocrine conditions, individual assessment is more appropriate than a generic calculator.

Worked examples

Deep dive

Methodology & assumptions

• Uses the Mifflin‑St Jeor predictive equations for resting energy expenditure.
• Applies sex‑specific constants (+5 for males, −161 for females) as defined in the formula.
• Requires weight in kilograms, height in centimeters, and age in years; other units must be converted first.
• Calculates a 24‑hour energy estimate at rest and labels it as BMR for planning purposes.
• Does not incorporate body fat percentage, lean mass, or medical conditions that can alter metabolism.
• Assumes adult inputs; not validated for children, pregnancy, or clinical nutrition scenarios.
• Performs arithmetic at full precision and rounds the displayed result for readability.
• Treats the output as a baseline estimate and leaves activity adjustment to the user.

Sources

• Mifflin MD et al. (1990) — A new predictive equation for resting energy expenditureOriginal publication of the Mifflin‑St Jeor equation.
• FAO/WHO/UNU — Human Energy Requirements (BMR definitions)Official report defining basal metabolic rate and energy requirement terminology.

FAQs

Is BMR the same as TDEE?

No. BMR estimates calories burned at rest only. Total Daily Energy Expenditure (TDEE) includes BMR plus all activity—walking, training, job demands, and other movement—often approximated by multiplying BMR by an activity factor.

Is BMR the same as RMR (resting metabolic rate)?

They’re closely related but not identical. BMR is measured under strict conditions and is typically slightly lower than RMR. Most practical calculators estimate resting energy expenditure and label it BMR for simplicity, which is usually fine for planning.

Should I adjust for body fat percentage?

For many people, Mifflin‑St Jeor is a good starting point without explicit body fat inputs. However, if you are very lean, very muscular, or at either extreme of body composition, equations that use lean body mass may give better estimates. A coach or clinician can help choose the right approach.

Why does my actual maintenance seem different from what BMR × activity factor suggests?

Human metabolism is variable. Stress, sleep, hormones, NEAT (unstructured movement), and genetics all influence real‑world calorie needs. Use BMR‑based estimates to set an initial target, then adjust based on weight and performance trends over time.

Is it safe to eat below my BMR?

BMR is a resting baseline, not a minimum safe intake. Some people eat below BMR during a calorie deficit, but the appropriateness depends on your size, goals, and health status. For medical or aggressive weight‑loss plans, consult a qualified professional.

How often should I recalculate my BMR?

Re‑calculate when your weight or lifestyle changes meaningfully (for example, every 5–10 lb of weight change, a new training phase, or yearly as you age), rather than obsessing over tiny day‑to‑day fluctuations.

What activity factor should I use to estimate maintenance?

Common multipliers range from about 1.2 (sedentary) up to 1.9 (very active). These are general guidelines—choose the factor that best matches your real daily movement and adjust based on actual results.

Does BMR change as I lose or gain weight?

Yes. Because the equation depends on weight and age, your estimate changes as those inputs change. Long‑term changes in lean mass and activity can also influence real energy needs beyond what the formula captures.

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