BMR and TDEE, Explained
After reading this you can estimate your resting calorie burn, scale it to a realistic daily total, and set a calorie target for losing or gaining weight while knowing how wide the error bars really are.
What these two numbers mean
Your basal metabolic rate (BMR) is the energy your body spends at complete rest to keep you alive: breathing, pumping blood, maintaining body temperature, running your organs. It is measured lying still, awake, fasted, in a comfortable room. For a 30-year-old man who is 175 cm and 70 kg, the Mifflin-St Jeor formula puts BMR near 1649 kcal per day. That is what he would burn doing nothing at all for 24 hours.
Your total daily energy expenditure (TDEE) is the whole picture: BMR plus the calories from moving, exercising, digesting food, and fidgeting. You get it by multiplying BMR by an activity factor. For that same man at a light activity level, the factor 1.375 gives a TDEE near 2267 kcal per day.
The gap between the two is large. The activity multiplier alone can swing your daily need by 700 kcal or more, which is why most people who want to manage their weight care about TDEE, not BMR.
When to use this, and when not to
Use a BMR and TDEE estimate to pick a sensible starting calorie target, to sanity-check a diet plan, or to understand why two people of the same weight can need very different amounts of food. It answers the question, "roughly how many calories do I burn in a day?"
Do not treat the output as a measured value. These formulas were fitted to groups of people, so they predict the average of a population, not you specifically. The published standard error for Mifflin-St Jeor is around 10 percent, meaning a predicted 2267 kcal could reasonably be anywhere from about 2040 to 2494 for a given person. Illness, medication, pregnancy, and eating disorders all change the picture, and none of them belong in a calculator.
Do not set a target below your BMR for long stretches. Eating under resting needs day after day is how people lose muscle and stall. If your goal number lands under BMR, choose a smaller deficit.
The formulas and the intuition behind them
Three formulas are offered. Two use only your body size, age, and sex. One uses your lean mass.
Mifflin-St Jeor is the recommended default because it tracks measured resting metabolism most closely for modern populations:
Here w is weight in kilograms, h is height in centimeters, a is age in years, and s is a sex constant: s = +5 for men and s = -161 for women. The intuition is direct. More mass and more height mean more tissue to fuel, so both raise BMR. Age lowers it, roughly 5 kcal per year, because metabolically active tissue tends to decline as you get older.
The revised Harris-Benedict formula does the same job with different coefficients and typically reads a little higher. Katch-McArdle ignores sex and age entirely and works from lean body mass:
Here bf is body fat percent, so w \cdot (1 - bf/100) is your fat-free mass in kilograms. This formula is the most accurate choice if you have a reliable body fat number, because muscle burns more at rest than fat does. Feed it a bad body fat guess and its advantage disappears.
From BMR to TDEE: the activity multiplier
To get TDEE you multiply BMR by a single factor that stands in for everything you do beyond lying still:
| Activity level | Factor f | TDEE (kcal) |
|---|---|---|
| Sedentary | 1.2 | 1979 |
| Light (1 to 3 sessions/week) | 1.375 | 2267 |
| Moderate (3 to 5 sessions/week) | 1.55 | 2556 |
| Active (6 to 7 sessions/week) | 1.725 | 2845 |
| Very active (physical job + training) | 1.9 | 3133 |
Notice the range. The same body needs 1979 kcal if sedentary and 3133 kcal if very active, a spread of over 1150 kcal. The activity factor is the single largest source of uncertainty in the whole calculation, and it is the one you choose by hand. Most people overestimate it. A few gym sessions a week is 1.375, not 1.725.
Reproducing the demo numbers
The demo uses the field defaults: male, 30 years, 175 cm, 70 kg, Mifflin-St Jeor, light activity.
- Weight term:
10 × 70 = 700. - Height term:
6.25 × 175 = 1093.75. - Age term:
-5 × 30 = -150. - Sex constant for a man:
+5. - Sum:
700 + 1093.75 - 150 + 5 = 1648.75, so BMR \approx 1649 kcal. - Apply the light factor:
1648.75 × 1.375 = 2267kcal, the TDEE.
For a weight-loss target, subtract a deficit. A common choice is 20 percent: 2267 × 0.8 ≈ 1814 kcal. That still sits above the BMR of 1649, which is what you want. For gaining, add a surplus of 10 to 15 percent: 2267 × 1.12 ≈ 2539 kcal.
Reading and interpreting the result
Treat the TDEE as the center of a range, not a fixed figure. Combine the formula uncertainty with your activity guess and the honest answer for the demo person is "somewhere near 2000 to 2500 kcal per day." The way to narrow it is not a better formula but data from your own body.
Weigh yourself several mornings a week and average the readings, then track how the average moves over two to three weeks against how much you ate. A pound of body fat holds roughly 3500 kcal, so losing about 0.5 kg (1.1 lb) per week corresponds to an average daily deficit near 550 kcal. If the scale is not moving the way the target predicts, adjust the calorie number by 100 to 200 kcal and watch again. The measured trend beats any estimate.
Common mistakes
A handful of errors account for most bad estimates.
- Overrating activity
- Choosing
1.725for three weekly workouts. If your job is desk-bound and you train a few times a week, you are light (1.375). The difference here is 578 kcal per day. - Double counting exercise
- The activity factor already includes your training. Do not add extra calories from a fitness tracker on top of the TDEE unless you deliberately chose the sedentary factor as your base.
- Guessing body fat for Katch-McArdle
- Katch-McArdle only helps with a real measurement. A body fat guess that is 5 points off shifts fat-free mass by about 3.5 kg and BMR by roughly 76 kcal.
- Chasing the decimal
- Reporting
2267kcal as if it were exact. The honest precision is about 200 kcal either way. Round to the nearest 50 and adjust from real data.
Related tools
BMR and TDEE describe energy. Two other measures describe your body composition and pair well with them. The BMI Calculator gives your body mass index, its WHO category, and a healthy weight range for your height, which is a quick check on whether your goal weight is reasonable. If you want to run the Katch-McArdle formula but do not have a body fat number, the Body Fat Estimator (Navy Method) derives one from tape measurements so you can feed it back into this calculator.
Frequently asked questions
Which formula should I use?
Use Mifflin-St Jeor unless you have a measured body fat percent, in which case Katch-McArdle can be slightly more accurate. Harris-Benedict is fine but tends to read a bit high. For the demo person the three agree to within about 100 kcal.
Why is my TDEE so different from a friend of the same weight?
Height, age, sex, lean mass, and above all activity level all feed in. Two people at 70 kg can differ by more than 1000 kcal in TDEE if one is sedentary and the other trains daily.
How big a deficit is safe for losing weight?
This calculator is educational and does not give medical advice. As a general rule people use a 10 to 20 percent deficit and keep the target above BMR. Larger deficits are harder to sustain and risk muscle loss. Speak with a professional before making changes.
How often should I recalculate?
Recalculate after your weight changes by a few kilograms, since BMR depends on weight. After a 5 kg loss the demo person's BMR drops by 50 kcal, and the TDEE at light activity drops by about 69 kcal.
Do the calories I burn digesting food count?
Yes. The thermic effect of food, roughly 10 percent of intake, is already folded into the activity multipliers, so you do not add it separately.
Related tools
BMI Calculator
Body mass index, WHO category and healthy weight range.
Child Growth Percentile Calculator
WHO percentile for a child's weight, height or head size.
Dynamic Weight Change Simulator
Realistic weight trajectory with metabolic adaptation.
Ideal Weight Calculator
Devine, Robinson, Miller and Hamwi targets plus BMI range.
Macro Calculator
Protein, carb and fat grams from your daily calories.
Body Fat Estimator (Navy Method)
Body fat percent from tape measurements only.