Basal Metabolic Rate Calculator

Your basal metabolic rate is the energy your body needs just to stay alive — to breathe, pump blood, keep warm and repair cells — while you lie completely still. For most adults it is 60 to 70 percent of everything they burn in a day, which makes it the most important number in any calorie plan. The basal metabolic rate calculator above works it out from your sex, age, weight and height, and compares all three standard formulas side by side.

This page explains what BMR is, how it is measured, which formula to trust, and how to turn your BMR into a daily calorie target. It also covers the factors that raise or lower your resting burn, and why two people of the same weight can have very different numbers.

What Basal Metabolic Rate Means

BMR is the minimum energy your body needs to run its basic systems. It is measured under strict conditions: after 12 hours without food, lying down, awake but completely at rest, in a comfortably warm room. That is why it is called basal — it is the baseline, before any movement at all. Your total daily burn is BMR plus everything else: walking, working, exercising and digesting food. Knowing BMR matters because it sets the floor of your energy needs; you cannot eat below it for long without your body slowing down to protect itself.

How the Calculator Works

The calculator uses your sex, age, weight and height in the Mifflin-St Jeor equation, then shows the same calculation with the two other standard formulas so you can compare. The default result is for a 30-year-old man, 70 kg, 175 cm: a BMR of 1,649 calories a day, or about 69 calories an hour at rest.

Check the Katch-McArdle column: for the woman at 60 kg and 20% body fat, lean mass is 48 kg, so BMR = 370 + 21.6 × 48 = 1,407 calories. For the man at 70 kg and 20% body fat, lean mass is 56 kg and BMR = 370 + 21.6 × 56 = 1,580 calories. The lesson is that Katch-McArdle depends entirely on the body fat number you feed it — a wrong body fat estimate gives a wrong BMR. Use the body fat calculator to get that number first.

Why Men and Women Differ

At the same weight, height and age, a man’s BMR is about 166 calories a day higher than a woman’s. The reason is body composition: men carry more muscle and less fat on average, and muscle burns roughly three times as much energy at rest as fat does. This is a population average, not a rule for individuals — a muscular woman will have a higher BMR than a sedentary man of the same weight. The formulas use sex as a rough proxy for muscle mass because they cannot measure it directly. If you know your body fat percentage, Katch-McArdle removes the guesswork by using your actual lean mass.

BMR by Age

BMR falls steadily with age, by about 5 calories a year in the formula. That sounds small, but over 30 years it is 150 calories a day — the equivalent of a snack you can no longer eat without gaining weight. Most of the fall is not age itself but the muscle lost with age: adults lose 3 to 8 percent of muscle mass per decade after 30, and muscle is the tissue that burns the calories. Strength training twice a week is the most effective way to slow the decline.

Verify one row: the man at 80 kg and 178 cm at age 45 has a BMR of 10 × 80 + 6.25 × 178 − 5 × 45 + 5 = 800 + 1,112.5 − 225 + 5 = 1,692.5, rounded to 1,693. The woman at 65 kg and 165 cm at age 35: 650 + 1,031.25 − 175 − 161 = 1,345.25, rounded to 1,345. Both match the table.

From BMR to Your Daily Calorie Needs

BMR is the starting point, not the finish. Multiply it by your activity factor to get your total daily energy expenditure — the calories that maintain your weight. The table below does it for the default man with a BMR of 1,649.

Once you have that number, your goal decides the target: subtract 500 for weight loss, add 500 for weight gain, or eat at maintenance to stay the same. The TDEE calculator does the multiplication and shows targets for every goal, and the calorie calculator adds macro splits on top.

What Affects Your BMR

• Muscle mass. The biggest factor you can change. Each kilogram of muscle burns about 13 calories a day at rest, against 4.5 for a kilogram of fat.
• Body weight. More tissue costs more energy to maintain — 10 calories a day per kilogram in the formula.
• Age. BMR falls about 5 calories a year, mostly through muscle loss.
• Sex. Men average about 166 calories a day higher at the same size, through higher muscle mass.
• Thyroid hormones. An overactive thyroid can raise BMR by 20 percent or more; an underactive one lowers it. If your weight changes unexpectedly, get your thyroid checked.
• Fever and illness. Each degree of fever raises BMR by roughly 7 to 13 percent.
• Pregnancy. BMR rises through pregnancy as the body supports the growing baby, by about 300 calories a day by the third trimester.
• Crash dieting. Very low calorie intake can lower BMR by 10 to 15 percent as the body adapts — one reason extreme diets backfire.

BMR Versus RMR: What Is the Difference?

You will also see the term resting metabolic rate (RMR). BMR and RMR measure almost the same thing, but RMR is measured under looser conditions — you do not need to fast for 12 hours or sleep in a lab. RMR is typically 10 to 20 percent higher than BMR because it includes the small energy cost of being awake and recently fed. In practice, most online calculators labelled BMR are really estimating RMR, and the difference is small enough that it does not matter for meal planning. What matters is using the same number consistently and adjusting from your results.

Common BMR Myths

• “Eating little meals all day raises BMR.” Meal frequency has almost no effect on resting burn. Total calories matter, not how often you eat them.
• “Green tea and chilli boost metabolism a lot.” The effect is real but tiny — tens of calories a day, not hundreds.
• “Thin people have fast metabolisms.” Usually the opposite: heavier people have higher BMRs because there is more body to maintain. What thin people often have is more daily movement.
• “BMR is fixed.” It changes with weight, muscle, age and diet. Recalculate it whenever your weight changes by 5 kg or more.

Related tools: turn BMR into daily needs with the TDEE calculator, get a full daily target with macros from the calorie calculator, and check your weight category with the BMI calculator. The National Heart, Lung, and Blood Institute has plain-language guidance on metabolism and healthy weight.

Key Takeaways

Use the bmr calculator above with your own numbers, and keep the reference figures below handy while you plan.

What to remember

• BMR is the calories you burn at complete rest — 60 to 70 percent of your daily total.
• Men burn about 166 calories a day more than women at the same size, through higher muscle mass.
• BMR falls about 5 calories a year, mostly through muscle loss.
• Mifflin-St Jeor is the most accurate formula for most adults; Katch-McArdle is best for very lean or muscular people.
• Multiply BMR by an activity factor (1.2 to 1.9) to get your daily calorie needs.

Your checklist

1. Enter your sex, age, weight and height in the calculator above.
2. Read your BMR and compare the three formulas.
3. Multiply by your activity level to get your daily needs.
4. Set your goal target: minus 500 for weight loss, plus 500 for gain.
5. Recalculate whenever your weight changes by 5 kg or more.

Mistakes to avoid

• Using pounds instead of kilograms — divide pounds by 2.205 first.
• Using the wrong constant: men add 5, women subtract 161.
• Treating BMR as daily needs — eating only your BMR is a large deficit.
• Forgetting the age term, which adds up to 150 calories between age 25 and 55.
• Crash dieting, which can suppress BMR by 10 to 15 percent.

Frequently Asked Questions

What is basal metabolic rate?

BMR is the calories your body burns at complete rest to keep you alive — breathing, circulation, temperature control and cell repair. For most adults it is 60 to 70 percent of total daily burn, typically 1,200 to 2,000 calories a day.

How is BMR different from TDEE?

BMR is rest only. TDEE is BMR plus all activity: walking, working, exercising and digesting food. TDEE is your maintenance calorie level, while BMR is the floor underneath it. Multiply BMR by 1.2 to 1.9 depending on activity to get TDEE.

Which BMR formula should I use?

Mifflin-St Jeor for most people — it is the most accurate for the general population. Use Katch-McArdle if you are very lean or muscular and know your body fat percentage, because it uses lean mass instead of total weight.

Can I increase my basal metabolic rate?

Yes, modestly, by building muscle. Each kilogram of muscle adds about 13 calories a day of resting burn, and strength training twice a week preserves muscle as you age. Eating enough protein supports the process. There is no food or supplement that raises BMR by a meaningful amount.

Why is my BMR low?

Usually because you are smaller, older, or carrying less muscle. Women average lower than men at the same size. Crash dieting also lowers BMR temporarily. If your BMR seems far below the tables for your size and you have unexplained weight gain or fatigue, ask your doctor about a thyroid check.

Do I eat my BMR or my TDEE?

Your TDEE. Eating only your BMR while living a normal active life creates a deficit of 400 to 1,000 calories a day, which is too large to sustain and costs muscle. BMR is the starting point for the calculation, not the target.

Disclaimer: This calculator provides estimates for general information only and is not medical advice. BMR equations are population averages and can be off by 10 percent or more for individuals. Consult a doctor or registered dietitian before using BMR to plan a diet, especially if you have a thyroid condition or other medical issue.