What Is Basal Metabolic Rate?
Your Basal Metabolic Rate (BMR) is the number of calories your body needs to sustain basic life functions at complete rest — things like breathing, circulating blood, regulating body temperature, and keeping your organs running. Think of it as the energy your body would burn if you stayed in bed all day without moving.
I built this calculator to help you understand the foundation of your energy needs. BMR is the starting point for calculating how many calories you actually need each day based on your activity level. Once you know your BMR, you can multiply it by an activity factor to find your Total Daily Energy Expenditure (TDEE).
Harris-Benedict vs. Mifflin-St Jeor Formula
There are two widely used formulas for estimating BMR. The original Harris-Benedict equation was developed in 1919 and revised in 1984. The Mifflin-St Jeor equation, published in 1990, is generally considered more accurate for most people today. Here is how they differ:
- Harris-Benedict (revised): tends to overestimate calorie needs slightly, especially in overweight individuals
- Mifflin-St Jeor: validated against indirect calorimetry in multiple studies; the formula most dietitians and the Academy of Nutrition and Dietetics recommend
- Both formulas use age, sex, height, and weight as inputs
This calculator uses the Mifflin-St Jeor equation by default, as the research consistently shows it provides a closer estimate for the general population.
How to Use Your BMR Result
Your BMR alone tells you the calories needed at rest. To find how many calories you need on a typical day, apply the appropriate activity multiplier:
- Sedentary (little or no exercise): BMR × 1.2
- Lightly active (1–3 days/week): BMR × 1.375
- Moderately active (3–5 days/week): BMR × 1.55
- Very active (6–7 days/week): BMR × 1.725
- Extra active (physical job or twice-daily training): BMR × 1.9
The result is your estimated maintenance calorie intake. To lose weight, create a modest deficit below this number. To gain muscle, eat slightly above it. Use the Daily Calorie Calculator on this site to do that math automatically.
Frequently Asked Questions
What is a good BMR?
There is no single "good" BMR — it varies widely based on body size, age, and sex. A taller, heavier, younger person will have a higher BMR than a shorter, lighter, older person. What matters more is using your BMR as a personal baseline to guide your calorie goals rather than comparing it to others.
Does BMR change over time?
Yes. BMR naturally decreases with age, partly because lean muscle mass tends to decline. Significant weight changes, crash dieting, and certain medical conditions can also affect it. Recalculate every few months or whenever your weight changes by more than 5–10 pounds for the most accurate estimate.
Is BMR the same as TDEE?
No. BMR is the calories burned at complete rest. TDEE (Total Daily Energy Expenditure) adds the calories burned through daily activities and exercise on top of your BMR. For most people, TDEE is 20–90% higher than their BMR. This is an estimate — consult a healthcare provider or registered dietitian for personalised nutrition advice.
