BMR vs TDEE: How Many Calories You Need
“How many calories should I eat?” has a real answer, and it starts with two acronyms: BMR and TDEE. Understand them and calorie targets stop being mysterious numbers from an app and start making sense.
BMR: what your body burns at rest
Your Basal Metabolic Rate is the energy your body uses just to stay alive — breathing, circulation, keeping your organs running — if you did nothing but lie still all day. For most adults it accounts for the majority of daily calorie burn, often 60–70%.
BMR scales with your size and body composition. More mass (including muscle) means a higher BMR, which is one reason strength training helps with long-term weight management: muscle is metabolically active tissue.
The Mifflin–St Jeor equation
The most widely trusted BMR formula for the general population is Mifflin–St Jeor:
- Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
A 30-year-old man at 175 cm and 70 kg has a BMR of about 1,649 calories. That is his floor — before he stands up, walks, or exercises.
TDEE: what you actually burn in a day
Total Daily Energy Expenditure is BMR plus everything else: walking to the kitchen, typing, fidgeting, workouts, even digesting food. You estimate it by multiplying BMR by an activity factor:
- Sedentary (desk job, little exercise) — × 1.2
- Lightly active (1–3 days/week) — × 1.375
- Moderately active (3–5 days/week) — × 1.55
- Very active (6–7 days/week) — × 1.725
- Extra active (hard training or physical job) — × 1.9
Our example man, moderately active, has a TDEE of about 1,649 × 1.55 ≈ 2,556 calories. That is his maintenance level — eat that and his weight stays roughly stable.
Setting a target: deficit and surplus
Weight change is driven by energy balance. A pound of body fat stores roughly 3,500 calories, so:
- To lose weight: eat below TDEE. A 500-calorie daily deficit predicts about 0.5 kg (1 lb) of loss per week — for our example, ~2,056 calories a day.
- To maintain: eat around TDEE.
- To gain: eat above TDEE. A modest 250–500 surplus supports muscle gain without excessive fat.
Why the honest activity level matters most
The single biggest source of error is overestimating activity. A few gym sessions a week does not make you “very active.” When people plateau on a diet, an inflated activity multiplier is usually why: their “deficit” was actually maintenance. If in doubt, pick the lower activity level.
The limits of any calorie formula
These equations are population averages. Real metabolism varies with genetics, hormones, sleep, medications and how much you unconsciously move (NEAT). Treat the number as a starting hypothesis, not a law:
- Set a target from the calculator.
- Track intake and weight for 2–3 weeks (weight fluctuates daily; watch the trend).
- If the scale is not moving the way you want, adjust by 100–200 calories and repeat.
Also avoid going too low. Very aggressive deficits cost muscle, tank energy and rarely last. For most people a loss of about 0.5–1% of body weight per week is sustainable.
Calories are not the whole story
Two diets at the same calorie count are not equal. Protein preserves muscle in a deficit and keeps you full; fiber-rich whole foods satisfy far better per calorie than ultra-processed ones. Hit your calorie target, but get enough protein and vegetables while you do.
This article is general information, not medical advice. Consult a doctor or registered dietitian for personalized guidance, especially if you have a health condition.
Calculate your numbers
Use the free Calorie Calculator to get your BMR, maintenance calories and targets for losing or gaining weight in seconds. To check where you fall on the weight-for-height scale, pair it with the BMI Calculator, and use the Percentage Calculator to work out your protein or deficit percentages.