BMR Calculator

What is a BMR Calculator?

This calculator estimates your Basal Metabolic Rate (BMR) — the number of calories your body burns at complete rest just to keep you alive (breathing, circulation, cell repair). It also shows your daily calorie needs (TDEE) for five different activity levels.

BMR typically accounts for 60-75% of all calories you burn in a day. Even lying in bed all day, your body still needs this many calories for basic functions.

How to Calculate BMR

Inputs

Input	How to enter
Gender	Select Male or Female. The formula uses different constants for each.
Age	Toggle between Age (enter directly) or Date of Birth (enter year/month/day — age is auto-calculated).
Height / Weight	Toggle between cm / kg (metric) or ft·in / lb (imperial). Values convert automatically when you switch.

What the Results Mean

Result	What it shows
BMR	Calories your body needs at complete rest (kcal/day). This is your baseline — never eat below this long-term.
Daily Calorie Needs	Five rows showing your estimated calorie needs at each activity level. Find the one that matches your lifestyle.

Activity Levels Explained

Level	Description	Who this fits
Sedentary (×1.2)	Little to no exercise, desk job	Office worker who drives to work
Lightly Active (×1.375)	Light exercise 1-3 days/week	Walking, light stretching, casual cycling
Moderately Active (×1.55)	Moderate exercise 3-5 days/week	Regular gym, jogging, swimming
Very Active (×1.725)	Hard exercise 6-7 days/week	Intense training, competitive sports
Extra Active (×1.9)	Very hard exercise + physical job	Professional athlete, heavy manual labor

Good Examples

Example 1: Office Worker (Male)

A 30-year-old male, 175 cm, 75 kg, desk job.

• Gender: Male, Age: 30, Height: 175, Weight: 75
• BMR: 1,694 kcal/day
• Sedentary TDEE: 2,033 kcal/day — this is his target to maintain weight

Example 2: Active Woman

A 25-year-old female, 163 cm, 58 kg, goes to the gym 4 times a week.

• Gender: Female, Age: 25, Height: 163, Weight: 58
• BMR: 1,353 kcal/day
• Moderately Active TDEE: 2,097 kcal/day — her maintenance calories

Example 3: Weight Loss Plan

Using Example 1’s numbers (Male, 30, BMR 1,694, Sedentary TDEE 2,033):

Goal	Daily calories	Weekly result
Maintain weight	~2,033 kcal	No change
Lose ~0.5 kg/week	~1,533 kcal (500 deficit)	~0.45 kg loss
Never go below	1,694 kcal (BMR)	Eating below BMR slows metabolism

The safe zone for weight loss is between your BMR and TDEE.

Example 4: Imperial Units

A 40-year-old female, 5’5”, 140 lb, lightly active.

• Gender: Female, Age: 40, Height: 5 ft 5 in, Weight: 140 lb
• BMR: ~1,339 kcal/day
• Lightly Active TDEE: ~1,841 kcal/day

How BMR Relates to Weight Management

• To lose weight: Eat fewer calories than your TDEE but never below your BMR. A 500 cal/day deficit ≈ ~0.45 kg (1 lb) loss per week.
• To maintain weight: Eat roughly your TDEE.
• To gain weight: Eat 250-500 cal/day above your TDEE for gradual, healthy gain.

Warning: Eating below your BMR long-term can slow your metabolism, cause muscle loss, fatigue, and nutrient deficiencies. Always aim for a moderate deficit above your BMR.

What Affects BMR?

Factor	Effect
Muscle mass	More muscle = higher BMR (muscle burns more calories at rest)
Age	BMR decreases with age, mainly due to muscle loss
Genetics	Some people naturally have faster/slower metabolisms
Hormones	Thyroid hormones strongly influence metabolic rate
Temperature	Cold exposure can temporarily increase BMR

The Mifflin-St Jeor Equation

This calculator uses the Mifflin-St Jeor equation, considered the most accurate BMR formula for most adults.

Males: $BMR = (10 \times weight*{kg}) + (6.25 \times height*{cm}) - (5 \times age) + 5$

Females: $BMR = (10 \times weight*{kg}) + (6.25 \times height*{cm}) - (5 \times age) - 161$

Frequently Asked Questions

How accurate is the Mifflin-St Jeor equation?

Accurate to within about 10% for most people. For precise measurements, indirect calorimetry (a clinical test) is the gold standard. But for everyday use, this equation is the most reliable.

What is the difference between BMR and RMR?

BMR is measured under very strict conditions (12-hour fast, darkened room, 8 hours of sleep). RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically 10-20% higher. In practice, the terms are often used interchangeably.

Why does gender affect BMR?

On average, males have more muscle mass and less body fat than females of the same weight, resulting in a higher BMR. The +5 (male) and -161 (female) constants account for these differences.

Should I eat below my BMR to lose weight faster?

No. Going below BMR can trigger adaptive thermogenesis — your body slows metabolism to conserve energy. This makes weight loss harder long-term and can cause fatigue, hair loss, and hormonal issues. Stay between BMR and TDEE.