March 16, 2018
Your Basal Metabolic Rate (BMR) is the number of calories your body needs at complete rest to maintain basic life functions (breathing, circulation, cell production, etc.). BMR accounts for about 60–70% of the calories you burn each day. In other words, even if you lay in bed all day, you’d still burn those calories.
Knowing your BMR is the first step in weight management: eat roughly your calorie burn to maintain weight, eat less to lose weight, or eat more to gain weight. A great place to start is to determine how many calories you burn a day. And it all begins with your Basal Metabolic Rate.
What Is BMR and Why It Matters
BMR is essentially your body’s baseline energy budget. It depends on factors like age, sex, height, and body composition. For example, more lean muscle increases BMR, while higher body fat or being older usually lowers it. To manage weight, think of BMR and your activity together (your Total Daily Energy Expenditure, or TDEE). In practical terms:
Maintain weight: Eat roughly the same number of calories you burn (TDEE).
Gain weight (muscle): Consume more calories than you burn.
Lose weight (fat): Consume fewer calories than you burn.
These principles make weight change straightforward: eat below your needs to lose weight; above to gain.
What Affects Your Basal Metabolic Rate?
Your basal metabolic rate (BMR) is influenced by a variety of factors—some you can control, and others you can’t. These include:
Genetics – Your inherited traits can affect how efficiently your body uses energy.
Age – BMR generally decreases with age due to a natural decline in muscle mass.
Sex – Men typically have higher BMRs than women, largely due to differences in muscle mass and hormone levels.
Hormones – Thyroid function and other hormonal factors play a role in regulating metabolism.
Body composition – The more lean muscle mass you have, the higher your BMR.
Temperature and climate – Living in a cold environment may increase BMR slightly as your body works harder to maintain body temperature.
Diet and caloric intake – Severe calorie restriction can reduce BMR as the body adapts to conserve energy.
Medications – Some drugs (like stimulants or thyroid medications) can raise BMR, while others may lower it.
Health status – Illness, injury, or chronic conditions can alter BMR.
Sleep quality – Poor sleep may negatively impact hormonal balance, affecting metabolic rate.
While some factors are outside your control,
body composition is one area where you can make a meaningful impact. Increasing lean muscle mass is one of the most effective ways to boost your resting calorie burn.
Tip: Incorporating strength training or high-intensity interval training (HIIT) into your routine can significantly increase muscle mass — and in turn, raise your BMR.
Studies have consistently shown that anaerobic exercises like resistance training contribute to long-term improvements in metabolic rate through increased lean tissue.
How to Calculate Basal Metabolic Rate
Calculating your BMR is quick once you have your basic stats:
Step 1: Record your weight (kg), height (cm), age, and sex.
Step 2: Plug them into a standard BMR formula. There are a few common equations; the most popular are Mifflin-St Jeor and Harris-Benedict which use weight, height, age, and gender. Another formula (Cunningham) uses lean body mass.
The table below compares these formulas:
Formula (Year) | Men (kcal/day) | Women (kcal/day) |
Mifflin–St Jeor (1990) | 10×weight(kg) + 6.25×height(cm) – 5×age + 5 | 10×weight + 6.25×height – 5×age – 161 |
Revised Harris–Benedict (1984) | 13.397×weight + 4.799×height – 5.677×age + 88.362 | 9.247×weight + 3.098×height – 4.330×age + 447.593 |
Cunningham (1980, LBM-based) | 500 + 22×lean body mass (kg) | 500 + 22×lean body mass (kg) |
Each formula gives an estimate of your BMR in calories/day.
Tip: Some body composition analyzers (like InBody scanners) measure your lean mass directly and output your BMR automatically. This can save you math and account for your actual muscle mass.
Once you compute your BMR, you have a baseline number of calories your body needs at rest.
Mifflin–St Jeor Equation
This is the most widely used and recommended formula for calculating BMR in healthy adults.
It uses your body weight, height, age, and sex. It’s often considered more accurate than the original Harris–Benedict formula.
Formula:
Men: BMR = 10 × weight (kg) + 6.25 × height (cm) – 5 × age (years) + 5
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) – 5 × age (years) – 161
Example (Woman):
Weight = 65 kg, Height = 165 cm, Age = 30
BMR = 10×65 + 6.25×165 – 5×30 – 161 = 650 + 1031.25 – 150 – 161 = 1,370 kcal/day
Revised Harris–Benedict Equation
This formula is slightly older but still used in clinical nutrition. Like Mifflin–St Jeor, it factors in weight, height, age, and sex. It may overestimate BMR slightly compared to newer models, but it’s still reasonably accurate for general use.
Formula:
Men: BMR = 13.397×weight + 4.799×height – 5.677×age + 88.362
Women: BMR = 9.247×weight + 3.098×height – 4.330×age + 447.593
Example (Man): Weight = 75 kg, Height = 178 cm, Age = 28
BMR = ~1,789 kcal/day
Cunningham Equation
For people who fall outside the assumed ranges—like athletes with higher muscle mass or very lean individuals—the Cunningham equation can offer better accuracy. It uses lean body mass (LBM) instead of total weight, which reflects how much metabolically active tissue you have.
Formula:
BMR = 500 + 22 × lean body mass (kg)
Example:
Lean Body Mass = 55 kg
BMR = 500 + 22×55 = 500 + 1,210 = 1,710 kcal/day
From BMR to TDEE: Calculating Daily Calorie Needs
Remember, your BMR is just the number of calories your body burns at rest and does not account for the calories you need to walk, talk, exercise, etc. When thinking about your caloric needs for a meal plan, you must account for your current activity level or your increased activity level if you plan to exercise more. To do that, convert your BMR to your Total Daily Energy Expenditure (TDEE).
To account for this, multiply your BMR by an activity factor to get your Total Daily Energy Expenditure (TDEE). Common multipliers are :
Sedentary (little or no exercise): BMR × 1.2
Lightly active (light exercise 1–3 days/week): BMR × 1.375
Moderately active (moderate exercise 3–5 days/week): BMR × 1.55
Very active (hard exercise 6–7 days/week): BMR × 1.725
Extra active (very hard daily exercise or physical job): BMR × 1.9
For example, if your BMR is ~1,680 kcal and you’re moderately active, your TDEE would be about 1,680×1.55 ≈ 2,600 kcal. That means to maintain your weight, you’d need roughly 2,600 calories per day.
Having your TDEE lets you plan your eating. To lose weight, you eat below this number; to gain weight, you eat above it.
How to Use BMR to Lose Weight
If fat loss is your goal, you need a calorie deficit — consume fewer calories than your TDEE. The exact deficit depends on how fast you want to lose.
A lot of resources will tell you that you need to subtract 500 calories from your diet each day to lose one pound of fat per week. This is based on the premise that one pound of fat represents 3,500 calories, and that by reducing your caloric intake by 500 over 7 days, you’ll reach a weekly loss of 3,500 calories or a pound of fat. You may have heard this rule before.
For someone with a high TDEE, cutting 500 might be fine; for someone with a lower TDEE (e.g. 1,400 kcal), cutting 500 could drop them dangerously low.
A safer approach is a moderate, consistent cut. Aim to eat about 200–500 calories below your TDEE each day. For example, a 300–500 kcal daily deficit typically leads to losing ~0.5–1 pound per week. The key is consistency: a small daily deficit compounded over weeks results in fat loss. After a week or two, re-check your progress (weight and body composition) and adjust as needed.
Steps to use BMR/TDEE for weight loss:
Calculate your TDEE (BMR × activity factor) to find maintenance calories.
Decide on a daily calorie goal below TDEE (e.g. TDEE – 300 kcal).
Do not eat fewer calories than your BMR. That threshold is the bare minimum your body needs. Eating below BMR can slow your metabolism and harm your health.
Track your intake and progress. Use a food diary or app to stay within your calorie goal.
After a period (1–2 weeks), reassess. If you’re losing fat, continue. If weight stalls, you may need a slightly bigger deficit or more activity.
Eat smart: You don’t have to starve. First cut out “empty” calories: soda, candy, alcohol, chips, etc. Many people can lose weight simply by ditching these. If you already eat clean, look to adjust portion sizes or swap high-calorie items for lower-calorie, nutrient-dense foods. Keep protein intake high to preserve muscle as you lose weight. In other words, when dieting aim for fat loss, not muscle loss. (Protein has a high thermic effect and keeps you full.)
How to Use BMR to Build Muscle
If your goal is to build lean muscle mass, it’s not enough to simply meet your daily caloric needs — you must consistently exceed them, and combine that surplus with strength training and proper nutrition.
To effectively build muscle, you start with your BMR, adjust for activity to calculate your TDEE, and then create a strategic calorie surplus above that.
Let’s walk through how this works in practice.
Start by converting your BMR into your TDEE using an activity multiplier that reflects your weekly exercise habits. For example, someone with a BMR of 1,679 kcal/day and a moderate activity level (multiplier: 1.55) would have a TDEE of approximately 2,602 calories/day. This is the number of calories required to maintain their current body weight given their activity level.
To gain lean mass, you need to eat above this number. Research suggests a surplus of around 15% over TDEE is effective for muscle gain without excessive fat gain. In our example, that means:
TDEE: 2,602 kcal/day
15% surplus: 390 kcal/day
Recommended intake: ~2,992 kcal/day, which can reasonably be rounded to 3,000 kcal/day
This caloric increase provides the additional energy your body needs to support new muscle tissue, especially when paired with resistance training.
But it’s not just about eating more — what you eat matters. The extra calories should come primarily from protein-rich foods and complex carbohydrates. Protein is essential for muscle repair and growth, but it isn’t limitless in its benefits. More isn’t always better.
Hitting your protein goal is important — but hitting your total energy target is essential. Without enough overall fuel, your body won’t have the resources to build muscle, no matter how well you train or how clean your macros look.
To make the most of your surplus:
Prioritize whole foods and balanced meals.
Include quality protein sources like lean meats, fish, dairy, eggs, legumes, and tofu.
Don’t skimp on carbohydrates — they provide the energy needed for intense training.
Use healthy fats (e.g., olive oil, nuts, avocado) to round out your meals and boost caloric density.
Finally, it’s important to monitor your progress. Weight alone won’t tell you if your gains are from fat or muscle.
Final Takeaways: Body Composition and BMR
As with any dietary plan, you want to know how long it will take to see results. Yes, you can just use an online calculator to get a quick snapshot of where your BMR is today, but it won’t be tailored to the changes you are making from your diet and exercise plan.
Remember, since your BMR is closely linked to your lean body mass, any changes will affect the number of calories you burn.
If you gain lean body mass, your energy needs are going to increase. You will need more calories to continue to fuel that growth.
On the other hand, if your goal is to lose weight and you are on a strict calorie deficit diet, you may end up losing lean body mass. When you lose lean body mass, your BMR will decrease and you may end up plateauing if you don’t make adjustments to your diet plan.
If you are looking for a more precise analysis before you start your health, get your body composition measured. Seek professional medical advice to come up with a plan that’s right for you.
Frequently Asked Questions
Should I eat below my BMR?
No. Your BMR is the minimum calories your body needs to maintain basic functions. Eating fewer calories than your BMR is not recommended. In fact, consuming below BMR can trigger your body to slow the metabolism and protect itself from perceived starvation.
What happens if I eat only my BMR?
If you eat exactly your BMR calories and remain mostly inactive, you will roughly maintain your weight, not lose it. That’s because you’re covering just your baseline needs. However, this leaves essentially no extra energy for exercise or daily activities, which can be very difficult to sustain. Over time, if you do eat only at your BMR and try to be active, you may feel fatigued or unsatisfied. In practice, weight loss strategies focus on eating below TDEE (which includes activity calories), not simply at or below BMR.
What’s the difference between BMR and Resting Metabolic Rate?
Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR) are often used interchangeably, but they have subtle differences. BMR is the number of calories your body needs to perform its most basic functions (like breathing and cell repair) under very strict conditions—typically measured after 8 hours of sleep and 12 hours of fasting, in a temperature-controlled environment. RMR, on the other hand, is slightly less precise and easier to measure, accounting for the energy your body uses at rest but under more typical, relaxed conditions. In practice, RMR is usually a bit higher than BMR, but both are reliable indicators of how many calories your body burns at rest.
