Calorie Calculator

Why this number is an estimate

Before anything else: the number this calculator returns is an educated guess, not a measurement. The Mifflin-St Jeor equation it uses was published in 1990 (Mifflin et al., American Journal of Clinical Nutrition 51(2):241-247) after the authors measured the resting energy expenditure of 498 adults using indirect calorimetry and fit a regression to predict BMR from age, sex, weight, and height. Their best-fitting equation explained roughly 71% of the variance in individual BMR. The remaining 29% — body composition, thyroid function, genetics, sleep, recent meals, ambient temperature — the formula cannot see.

Two people of identical sex, age, weight, and height can have BMRs that differ by 200-300 kcal/day. The number above is the population average for someone matching your inputs. Your individual value sits somewhere within a roughly ±10% band around it. Treat it as a starting target, then adjust based on what actually happens to your weight over 2-3 weeks.

The Mifflin-St Jeor equation, written out

Basal Metabolic Rate (BMR), in kilocalories per day:

• Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) + 5
• Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) − 161

Worked example: a 35-year-old woman, 165 cm tall, 65 kg. BMR = (10 × 65) + (6.25 × 165) − (5 × 35) − 161 = 650 + 1,031.25 − 175 − 161 = 1,345 kcal/day. That is the energy her body burns lying still in a thermoneutral room for 24 hours. Add activity to get the daily total.

When other formulas are worth running

Mifflin-St Jeor is the default because it has the lowest mean error across mixed populations. Two alternatives sometimes do better:

• Katch-McArdle uses lean body mass instead of total body mass. If you know your body-fat percentage (from a DEXA, BodPod, or the body-fat calculator), Katch-McArdle is more accurate for athletes and lean individuals. Formula: BMR = 370 + 21.6 × lean mass(kg).
• Harris-Benedict (revised 1984) was the standard before Mifflin-St Jeor displaced it. It tends to slightly overestimate BMR in modern populations (Mifflin's authors specifically critiqued it on this point), but it is still occasionally cited in clinical settings.

For most people without a body-fat measurement, Mifflin-St Jeor is the right default. If you have actual body-composition data, Katch-McArdle is the right upgrade.

The activity multiplier is where the estimate goes wrong

TDEE = BMR × activity factor. The factors are:

• 1.2 — Sedentary: desk job, no deliberate exercise.
• 1.375 — Light: 1-3 workouts per week.
• 1.55 — Moderate: 3-5 workouts per week.
• 1.725 — Active: 6-7 workouts per week.
• 1.9 — Very active: intense daily training or a physically demanding job.

The honest observation: most people overestimate which bucket they fall into. Three gym sessions per week of moderate intensity is closer to 1.375 than 1.55 once you account for the rest of the week being sedentary. Real-world calorimetry studies consistently find that self-reported activity overstates measured energy expenditure by 15-30%. If your weight is not moving the way the calculator predicts after two weeks, drop the activity multiplier by one step rather than your calories. The activity factor is the noisier input.

Using the number to set a goal

Once TDEE is in the right ballpark for you, weight management is bookkeeping:

• Loss of ~0.5 kg/week: eat ~500 kcal/day below TDEE. The calorie-deficit calculator and weight-loss calculator set an exact target.
• Slow loss (~0.25 kg/week): ~250 kcal/day below TDEE. Easier to sustain; less muscle loss.
• Lean gain: ~250-500 kcal/day above TDEE, paired with resistance training. The bulking-calorie calculator handles this case.
• Maintenance: at TDEE.

Two thresholds to know: very low energy intake (below ~1,200 kcal/day for women, ~1,500 for men) sustained for weeks tends to slow BMR by 10-15% as the body adapts — the deficit shrinks toward zero. And weight loss is non-linear; the BMR-based deficit you set today will overshoot once you have lost 5-10% of your starting weight, because BMR drops with weight. Recalculate every few months.

For splitting the daily calorie target into protein, fat, and carbohydrate, use the macro calculator (or the keto calculator for a low-carb split). For the underlying screening number, the BMI calculator is a starting point with its own caveats.