BMR Calculator

What is Basal Metabolic Rate (BMR)?

Basal Metabolic Rate (BMR) represents the minimum number of calories your body needs to perform vital functions while completely at rest—in a warm, quiet room, after a full night’s sleep, and in a fasted state.

These functions include breathing, maintaining body temperature, circulating blood, regenerating cells, and keeping organs functioning. It’s your body’s baseline “energy cost of living.”

Because maintaining your organs consumes energy 24/7, your BMR typically makes up **60–75% of your total daily calorie burn**.

How the BMR calculator works

The calculator estimates your Basal Metabolic Rate (BMR) using well-validated equations derived from large cohorts. BMR reflects the calories your body needs at complete rest for core functions like circulation, breathing, thermoregulation, and cellular maintenance.

The most common formulas

• Mifflin–St Jeor (modern default):
  Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
  Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
• Harris–Benedict (revised):
  Men: BMR = 66.5 + (13.75 × weight kg) + (5.003 × height cm) − (6.75 × age)
  Women: BMR = 655.1 + (9.563 × weight kg) + (1.850 × height cm) − (4.676 × age)
• Katch–McArdle (needs lean mass):
  BMR = 370 + (21.6 × lean mass kg)
  This is identity-agnostic and often the best choice if you know your lean mass from a DEXA, BIA, or skinfold estimate.

About sex/gender inputs and inclusivity

Traditional equations were developed on cisgender cohorts and use sex-specific coefficients as rough proxies for average body composition. Our calculator includes Trans Male (on HRT), Trans Female (on HRT), and Non-binary / Other options so you can choose what best reflects your current body and identity. Here’s how to pick:

• Trans Female (on HRT): If you have been on estrogen/anti-androgen therapy and your current body composition resembles typical female averages, select this. Coefficients will usually be closer to the female version of the equations.
• Trans Male (on HRT): If you have been on testosterone and your current body composition resembles typical male averages, select this. Coefficients will usually be closer to the male version.
• Non-binary / Other: If you prefer not to map to the male/female coefficients, you can select a neutral option. You may also consider the Katch–McArdle formula with lean mass, which avoids sex-based coefficients entirely.

Practical tip: If you are early in transition or your body composition is changing, you can compute a range using both male- and female-based outputs and treat your needs as likely falling in between. Re-check periodically as your lean mass changes.

These equations provide estimates. Real-world energy needs vary with body composition, hormones, genetics, sleep, stress, and daily activity. For individualized guidance, talk to a clinician or registered dietitian.

Inclusive guidance for trans, non-binary, and intersex users

Your energy needs are personal. Hormone therapy (HRT) and changes in lean mass can shift BMR over time. This tool is designed to be inclusive by offering identity options and a formula (Katch–McArdle) that relies on lean mass rather than sex-based coefficients.

What HRT can do to BMR (high-level, individual results vary)

• Estrogen + anti-androgens: Often reduce lean mass and may lower BMR slightly over months.
• Testosterone: Often increases lean mass and may raise BMR, especially with resistance training and adequate protein.

If possible, estimate your lean mass (DEXA scan, multi-frequency BIA, or skinfolds) and use Katch–McArdle for the most identity-agnostic BMR estimate. If lean mass is unknown, choose the identity that reflects your current body, or bracket a range using both coefficient sets (male/female) and revisit as your composition changes.

Language note: We use “male/female coefficients” only to refer to how legacy equations were originally derived. Your gender identity is respected and supported throughout the app.

BMR vs. TDEE – What’s the difference?

While BMR measures your energy use at complete rest, TDEE (Total Daily Energy Expenditure) includes everything else—movement, exercise, digestion, and even fidgeting.

To estimate TDEE, you multiply your BMR by an activity factor:

This gives your total daily calorie needs—the number you’d need to maintain your current weight.

What affects tour BMR?

Everyone’s metabolism is unique. Your BMR depends on several biological and environmental factors:

• Muscle mass: Muscle tissue burns more calories than fat, even at rest.
• Age: BMR tends to decrease with age due to loss of lean tissue.
• Hormones & HRT: Thyroid hormones and sex hormones influence lean mass and BMR; HRT during transition can shift energy needs as composition changes.
• Gender identity selection in tools: In sex-based equations, pick the option that best reflects your current body composition. When in doubt, use Katch–McArdle with lean mass.
• Genetics: Some people naturally burn calories faster or slower.
• Climate: Colder environments slightly raise BMR for thermoregulation.
• Dieting history: Repeated aggressive restriction can temporarily reduce BMR (adaptive thermogenesis).

Why knowing your BMR matters

Knowing your BMR is the foundation of effective nutrition and fitness planning. It helps you set realistic calorie targets for:

• Weight loss: Eating fewer calories than your TDEE (but not below BMR) promotes gradual fat loss.
• Weight maintenance: Matching your intake to TDEE keeps weight stable.
• Muscle gain: Eating slightly above TDEE supports muscle growth when combined with resistance training.

BMR helps you understand how much energy your body needs just to exist—everything else you eat fuels movement, digestion, and activity.

BMR and health: The bigger picture

While BMR is often used for weight management, it also reflects your overall metabolic health. Unusually high or low BMR values may indicate thyroid issues, muscle atrophy, or metabolic adaptation from extreme dieting.

Combining your BMR with measurements like BMI, body fat percentage, and waist circumference gives a more complete view of your health profile.

How to use the BMR calculator

Simply enter your age, gender, height, and weight. The calculator automatically applies the Mifflin–St Jeor equation and gives you an estimate of your daily resting calorie burn. You can use this number as a baseline to determine your daily calorie targets.

Tip: Pair this with the TDEE Calculator to estimate your total energy needs, and the Macro Calculator to balance nutrients based on your goals.

From BMR to real life: Adjusting for accuracy

Your actual calorie needs can vary from calculated BMR due to differences in metabolism, sleep, stress, and genetics. Treat your BMR as a starting estimate—not an absolute rule.

• Monitor your weight over 2–3 weeks. If it changes faster or slower than expected, adjust your calorie intake by ±5–10%.
• Track energy levels, hunger, and recovery. Metabolism responds dynamically to your habits and energy balance.
• Recalculate BMR after significant weight or activity changes for more precise planning.