The Complete and Simple Guide to Basal Metabolic Rate (BMR)
Your BMR, referred to as your body's "engine-idle speed," represents the calories your body uses to maintain life. These are the calories it takes to keep your heart beating, your lungs moving air in and out, and your cells thicketing away merrily. Knowing your BMR lets you calculate how much to eat, without guesswork. Whether you want to lose body weight, maintain it or build muscle—this is important information.
For most people, about 60–75% of the calories they burn daily come from their BMR. The rest is moving, taking care of business, digestion and other activities. Once you know your BMR and how active your lifestyle is, you can calculate your Total Daily Energy Expenditure (TDEE), which is all the calories you burn over a day. That number is a good benchmark for planning your calorie intake moving forward.
How Body Uses Energy at Rest
Even when you're lying there doing absolutely nothing, your body is burning away at the grindstone in the background. Your brain alone is responsible for around 20% of your daily energy use; your liver and kidneys together have another 20–25%, while your heart accounts for ten percent. Your muscles, meanwhile—even when you're not exercising—can consume up to 30% of the diurnal total BMR figure. Fat uses way less, and this is why more muscle means a faster metabolic rate.
So basically, your BMR is the amount of energy your body requires just to keep each of these processes up and running: making and repairing cells, pumping the blood around, taking in air, balancing body temperature through sweat or panting like a dog after a run in July. You see? It's the least amount of energy needed to run the body properly every single day.
How to Calculate BMR
There are a number of ways to estimate BMR. The Harris-Benedict formula (from 1919!) was one of the earliest and it still works pretty well as far as we know. However, for most modern bodies the Mifflin-St Jeor equation (from 1990) is probably more accurate.
💡 Tip:
Lift weights often. Eat enough protein. Get 7+ hours of sleep per night. Find ways to reduce stress. Avoid crash dieting—gentle adjustments are best.
Common Blunders
❌ Don't eat at your BMR—it can be much lower or higher.
❌ Don't think of your basal metabolism as completely “broken.” Age, however, does take its toll.
❌ Don't try to speed up metabolism by changing the number of meals you eat each day.
❌ Don't rely on cardiovascular exercise alone instead of building muscle.
Bottom Line
Your Basal Metabolic Rate (BMR) is the number of calories your body requires to survive each day. The Total Daily Energy Expenditure (TDEE) is the calories it takes for you to function day in and out. Measure them together, and you have the foundation for any effective fitness or nutrition plan. Use BMR as a starting point rather than a hard-and-fast rule. Then adjust upwards as progress, sleep and stress suggest. Right then! After eating; first thing tomorrow it's off to the gym.