“How many calories should I eat?” is one of the most searched health questions, and yet most generic answers — like the old “2,000 calories a day” label seen on nutrition facts panels — are population averages that may be far off for any specific individual.
The most widely validated equation among nutrition researchers today is the Mifflin-St Jeor equation, published in 1990 and shown in later studies to be more accurate than the older Harris-Benedict equation it replaced.
It calculates your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest just to keep your organs functioning:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
BMR alone underestimates your real needs, because it does not include movement. To get your Total Daily Energy Expenditure (TDEE) — the number that actually matters for weight management — multiply BMR by an activity factor:
| Activity level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little to no exercise | 1.2 |
| Light | Light exercise 1–3 days/week | 1.375 |
| Moderate | Moderate exercise 3–5 days/week | 1.55 |
| Active | Hard exercise 6–7 days/week | 1.725 |
| Very active | Athlete-level training, physical job | 1.9 |
A 35-year-old woman, 65kg, 165cm tall, with a moderately active lifestyle:
BMR = 10(65) + 6.25(165) − 5(35) − 161 = 650 + 1031.25 − 175 − 161 = 1,345 kcal
TDEE = 1,345 × 1.55 = ~2,085 kcal/day to maintain current weight
Once you know your maintenance calories (TDEE), goals follow simple math:
Most people who "eat at a deficit but don't lose weight" are colliding with one of four well-documented errors, not a broken metabolism:
Under-counting intake. Studies consistently find people under-report what they eat by 20–40% — oils, sauces, drinks, bites while cooking, and generous "tablespoons" all vanish from the mental ledger. Weighing food for even one honest week is eye-opening.
Over-crediting exercise. Cardio machines and fitness watches routinely overstate burn by 20–40%, and "I earned this" eating after workouts often exceeds the workout itself. If you eat back exercise calories, eat back half at most.
Weekend drift. Five disciplined weekdays can be fully undone by two unmeasured weekend days — a 500-calorie daily deficit is only 2,500 for the week if Saturday and Sunday erase the other 1,000.
Ignoring adaptation. As you lose weight, your TDEE falls — a lighter body burns less, and metabolism adapts slightly beyond that. A target that produced steady loss at your old weight eventually becomes maintenance; recalculate every 10 lbs or so.
Mifflin-St Jeor gives a solid, evidence-based starting point — but treat the number as a baseline to adjust from based on how your actual weight trends over 2–3 weeks, not a fixed target carved in stone. Calculate your own maintenance calories with our calorie calculator.
Cautiously — device estimates run high. A common approach is to eat back no more than half of estimated exercise calories, then adjust based on what your weight actually does over two to three weeks.
Early loss includes water weight, which flatters the first weeks. Later stalls usually mean your TDEE has dropped with your weight, or intake has quietly crept up. Recalculate your needs at your new weight and re-tighten tracking before assuming a plateau.
BMR is what your body burns at complete rest; TDEE adds everything else — movement, exercise, digestion. You budget calories against TDEE, not BMR, and eating consistently below BMR is neither necessary nor advisable for most people.
Put these numbers into practice with our free calculator — no sign-up required.
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