Your body burns calories even when you do nothing. This calculator estimates that number using three established formulas, so you know the baseline your nutrition should never fall below.
BMR Calculator
Find how many calories your body burns at rest
| Timeframe | Calories Burned at Rest |
|---|---|
| Per hour | - |
| Per day | - |
| Per week | - |
| Per month | - |
| Per year | - |
| Activity Level | Daily Calories |
|---|
Disclaimer: This BMR calculator provides estimates based on established formulas. Actual metabolic rate varies based on genetics, body composition, hormonal factors, and health conditions. The only way to measure BMR precisely is through indirect calorimetry in a clinical setting. Use these results as a starting point for nutrition planning. Consult a healthcare professional or registered dietitian for personalized guidance.
How to Use This Calculator
Enter your gender, age, height, and weight. If you know your body fat percentage, add it in the optional field to unlock the Katch-McArdle formula, which uses lean body mass for a more personalized result.
The calculator runs all available formulas simultaneously and shows each result side by side. The Mifflin-St Jeor result is highlighted as the primary number because research supports it as the most accurate for most people.
What is BMR?
BMR stands for Basal Metabolic Rate. It’s the number of calories your body burns in 24 hours at complete rest, in a post-absorptive state (meaning you haven’t eaten for 12+ hours), in a temperature-neutral environment.
Think of it as the energy cost of simply being alive. Breathing, circulating blood, maintaining body temperature, repairing cells, running your brain. For most people, BMR accounts for 60 to 70% of total daily calorie expenditure. It’s by far the largest component.
What is the Difference Between BMR and RMR?
BMR and RMR (Resting Metabolic Rate) are often used interchangeably, but they’re measured under slightly different conditions.
BMR is measured under strict conditions: 12-hour fast, no exercise for 24 hours, lying completely still, in a darkened room. RMR is measured under more relaxed conditions, typically after a shorter fast and without the same environmental controls.
RMR is usually about 3 to 5% higher than BMR because the measurement conditions are less restrictive. For practical purposes, the difference is small enough that most calculators treat them as the same number.
What formulas does this Calculator use?
Mifflin-St Jeor (1990) is the recommended formula. It was developed from a large dataset and has been validated in multiple studies as the most accurate widely used BMR equation. The Academy of Nutrition and Dietetics recommends it for clinical use. It’s accurate within 10% for about 82% of people.
Harris-Benedict (1919, revised 1984) is the oldest and most well-known BMR formula. It was the standard for decades but has been shown to overestimate BMR by about 5% compared to measured values, particularly in overweight individuals. It’s included here for comparison.
Katch-McArdle takes a different approach entirely. Instead of using height, weight, age, and gender, it uses only lean body mass. This makes it potentially more accurate for people who know their body fat percentage, especially those with above-average muscle mass or very low body fat. It only appears if you enter a body fat percentage.
Why do the formulas give different numbers?
Because each formula was built from different data, using different populations, with different variables. Mifflin-St Jeor uses weight, height, age, and gender. Harris-Benedict uses the same variables but with different coefficients derived from 1919 data. Katch-McArdle ignores all of those and uses only lean body mass.
A difference of 50 to 150 calories between formulas is normal. If two formulas agree closely and the third is an outlier, the consensus is probably more reliable. If all three disagree significantly, it may indicate that your body composition doesn’t fit the standard assumptions, and clinical measurement would give a better answer.
Should I eat below my BMR?
In most cases, no. Your BMR represents the minimum energy your body needs to maintain basic functions. Consistently eating below this number signals your body that energy is scarce.
The typical responses include metabolic adaptation (your body deliberately slows calorie burning), muscle catabolism (your body breaks down muscle for fuel), hormonal disruption (particularly thyroid, cortisol, and reproductive hormones), increased hunger and cravings, and fatigue.
Very low calorie diets that fall below BMR should only be followed under medical supervision. For sustainable fat loss, a moderate deficit from your TDEE (not your BMR) is the recommended approach.
What factors affect BMR?
Several factors influence how many calories your body burns at rest.
Muscle mass is the biggest controllable factor. Muscle tissue is metabolically active and burns significantly more calories at rest than fat tissue. This is why strength training is one of the most effective ways to increase your BMR over time.
Age decreases BMR gradually, roughly 1 to 2% per decade after age 20. This is partly due to natural muscle loss (sarcopenia) and partly due to hormonal changes.
Gender matters because men typically have higher BMR than women of the same weight, primarily due to having more muscle mass and less body fat on average.
Genetics set the baseline. Some people are born with naturally faster or slower metabolisms. The DEC2 gene, thyroid hormone levels, and mitochondrial efficiency all play a role.
Body size directly correlates with BMR. A larger body requires more energy to maintain. This is why BMR decreases as you lose weight.
Can I increase my BMR?
Yes, but the options are limited and the gains are modest.
Build muscle through strength training. Each kilogram of muscle burns roughly 13 calories per day at rest, compared to about 4.5 for fat. Gaining 5 kg of muscle would increase your BMR by about 40 to 45 calories per day. That’s meaningful over time, though not dramatic.
Stay active throughout the day. NEAT (Non-Exercise Activity Thermogenesis), which includes fidgeting, walking, standing, and general movement, contributes to overall energy expenditure, though this affects TDEE rather than BMR directly.
Get enough sleep. Sleep deprivation has been shown to reduce resting metabolic rate by 2 to 8%. Consistent, quality sleep supports healthy metabolic function.
Eat enough protein. Protein has a higher thermic effect than carbs or fat, meaning your body burns more calories digesting it. This affects total daily expenditure more than BMR itself, but it supports muscle maintenance which protects BMR.
How does BMR relate to weight loss?
Your BMR is the floor. Your TDEE (BMR multiplied by an activity factor) is the ceiling for weight maintenance. The gap between what you eat and your TDEE determines whether you lose, maintain, or gain weight.
A safe and sustainable approach is to eat 15 to 20% below your TDEE while staying above your BMR. This creates a moderate deficit that supports fat loss at roughly 0.5 to 1 kg per week without triggering the metabolic adaptations that come with extreme restriction.
The results include a TDEE preview table that shows what your total burn looks like at each activity level. For detailed calorie and goal planning, use our TDEE Calculator.
How often should I recalculate my BMR?
Every time your body changes meaningfully. Losing or gaining more than 5 kg, gaining significant muscle mass, aging by several years, or experiencing hormonal changes (like menopause or thyroid treatment) can all shift your BMR.
For active dieters, recalculating every 4 to 6 weeks makes sense. As you lose weight, your BMR decreases because there’s less body to fuel. Updating your numbers keeps your calorie targets accurate.
Frequently Asked Questions
How accurate is a duWhat is a normal BMR?
For adult women, BMR typically falls between 1,200 and 1,600 calories per day. For adult men, it’s usually between 1,600 and 2,000. The exact number depends on age, height, weight, and body composition. There’s no single “normal” because everyone’s body is different.e date calculator?
Is BMR the same as metabolism?
BMR is one component of metabolism, but not the whole picture. Your total metabolism includes BMR (60-70%), the thermic effect of food (about 10%), and physical activity (20-30%). When people say they have a “fast” or “slow” metabolism, they’re usually referring to differences in BMR.
Why is my BMR so high?
High BMR typically reflects larger body size, higher muscle mass, younger age, or male gender. All of these factors increase the energy your body needs at rest. A high BMR isn’t a problem. It simply means your body requires more fuel.
Why is my BMR so low?
Low BMR is usually related to smaller body size, lower muscle mass, older age, or female gender. Chronic under-eating can also suppress BMR through metabolic adaptation. If your BMR seems unusually low and you’ve been restricting calories heavily, it may be worth consulting a dietitian.
What is the most accurate BMR formula?
The Mifflin-St Jeor equation is considered the most accurate for most people, predicting within 10% of measured values for about 82% of individuals. If you know your body fat percentage, the Katch-McArdle formula may be more accurate because it accounts for lean mass directly.
How is BMR measured in a clinical setting?
The gold standard is indirect calorimetry, which measures oxygen consumption and carbon dioxide production while you rest. The test takes about 15 to 30 minutes and is available at many sports medicine clinics and hospitals. It costs between $100 and $300 depending on location.
Related Articles on DebugMD
- What Happens When You Stop Eating Sugar for 30 Days – Cutting sugar supports metabolic health without requiring you to drop below your BMR.
Disclaimer: This BMR calculator provides estimates based on established formulas. Actual metabolic rate varies based on genetics, body composition, hormonal factors, and health conditions. The only way to measure BMR precisely is through indirect calorimetry in a clinical setting. Use these results as a starting point for nutrition planning. Consult a healthcare professional or registered dietitian for personalized guidance.