BMR vs TDEE: The Difference, and Which Number to Eat To
BMR is what you burn lying still; TDEE is what you burn living your day. Mixing them up is one of the most common reasons a diet stalls or feels impossible. Here is how they relate.
BMR, your basal metabolic rate, is the energy your body uses at complete rest. TDEE, your total daily energy expenditure, is BMR plus everything else you do in a day. BMR is the floor; TDEE is the whole house. For deciding how much to eat, TDEE is the number that matters. BMR is a building block inside it.
BMR: the cost of staying alive
If you spent 24 hours lying still in a comfortable room, your body would still burn a lot of energy keeping your heart beating, your lungs breathing, your brain working and your temperature steady. That is your BMR. For most adults it lands somewhere between 1,200 and 2,000 calories a day, and it is driven mainly by lean body mass: muscle, organs and bone. That is why it rises with body size and why men, who on average carry more lean mass, tend to have higher values than women of the same weight.
Measuring BMR properly takes a lab: you arrive fasted after a night’s sleep and lie under a hood that analyses your breath. Most people never do that, so we estimate it with equations fitted to people who did.
The equations
- Mifflin-St Jeor (1990) uses weight, height, age and sex. In a 2005 systematic review of prediction equations in the Journal of the American Dietetic Association, it was the one most often within 10% of measured values in healthy adults.
- Harris-Benedict, first published in 1918 and revised by Roza and Shizgal in 1984, uses the same inputs with different weights. It tends to read a little higher than Mifflin-St Jeor.
- Katch-McArdle and Cunningham use lean body mass instead of total weight. They suit people whose body composition is far from average, such as lean athletes, provided the body-fat figure is reasonably accurate.
Our TDEE calculator averages the first two and adds the lean-mass equations when you enter a body-fat percentage, then shows each result so you can see how close they are. If they disagree a lot, that is a sign your body composition is unusual and the lean-mass figures deserve more weight.
TDEE: everything else on top
TDEE adds three things to BMR:
- Daily movement outside exercise — your job, walking, chores, standing.
- Exercise — the workouts you plan.
- Digestion — roughly 10% of what you eat.
The ratio between the two numbers, TDEE ÷ BMR, is called the physical activity level. In the FAO/WHO/UNU framework, 1.40 to 1.69 is a sedentary or light lifestyle, 1.70 to 1.99 active, and 2.00 or more vigorous. So a person with a BMR of 1,500 calories might burn 2,150 on a desk-bound day and 2,900 on a physically demanding one.
A worked example
Take a 40-year-old woman, 165 cm and 68 kg, who works at a desk, walks about 6,000 steps a day and goes to a spin class twice a week.
- Mifflin-St Jeor BMR: 10 × 68 + 6.25 × 165 − 5 × 40 − 161 ≈ 1,350 calories.
- Revised Harris-Benedict: ≈ 1,410. Average: about 1,380.
- Add her desk job, her steps, two classes a week and digestion, and the calculator puts her TDEE at roughly 2,200, a PAL of about 1.6.
If she wanted to lose fat and set her intake at her BMR of 1,380, she would be eating around 820 calories under her TDEE every day — well over a third of her needs. If she set it 15% under TDEE instead, about 1,880, the deficit would be roughly 330 calories: slower, but far easier to keep up while protecting muscle.
Why “eat your BMR” is poor advice
It is a popular rule on social media, and it confuses the two numbers. Eating at BMR is not a neutral setting; for most people it is a deep deficit. Large deficits make it harder to hit protein, harder to train, and more likely to end in a rebound. The better approach is to estimate TDEE, choose a deficit you can hold for months, and check it against your weight trend.
Which number to use for what
| You want to… | Use |
|---|---|
| Know how much to eat to keep your weight | TDEE |
| Set a fat-loss or muscle-gain target | TDEE, minus or plus a percentage |
| Set a safe lower limit for intake | Roughly BMR — avoid going under it without supervision |
| Compare yourself with others or track ageing | BMR |
Ready to work out both? The TDEE calculator shows your BMR from each equation, your TDEE and calorie targets for six goals in one go.
Frequently asked questions
Should I eat my BMR to lose weight?
Usually not. Eating at your BMR means a deficit equal to everything you burn through movement and digestion, which for most people is 30 to 50% of their TDEE. That is hard to sustain and makes it harder to keep muscle. A target 10 to 20% under TDEE works better for most.
Is BMR the same as RMR?
Nearly. Basal metabolic rate is measured under strict conditions: after a night's sleep, fasted, lying still in a warm room. Resting metabolic rate is measured under looser conditions and comes out slightly higher. Prediction equations are often used for either.
Which BMR equation is most accurate?
For most healthy adults, Mifflin-St Jeor has been the most consistent in comparisons with measured values. Equations based on lean mass, such as Katch-McArdle and Cunningham, do better for very muscular or very lean people, but only if you know your body fat accurately.
Why is my TDEE so much higher than my BMR?
Because everything you do above lying still adds to it. A typical office worker's TDEE is around 1.4 to 1.5 times BMR; an active person can be at 1.8 or more.