How Calories Are Calculated: Mifflin-St Jeor, Explained
The Mifflin-St Jeor equation for BMR, the activity multipliers that turn it into daily calories, and why the multiplier is where most estimates go wrong.
2026-09-05 · Health
BMR first
Men: 10 × weight + 6.25 × height − 5 × age + 5. Women: the same but − 161. A 30-year-old male at 75 kg and 175 cm gets 1,682 kcal at rest.
Then activity
Multiply by 1.2 (sedentary), 1.375 (light), 1.55 (moderate), 1.725 (very active) or 1.9 (athlete). The same person at 1.55 lands at 2,607 kcal.
Where estimates break
People overestimate activity and under-count liquid calories. If the scale has not moved in two weeks, lower the multiplier before cutting food.
Turning it into a plan
A 500 kcal daily deficit is roughly 0.45 kg a week. Bigger deficits cost muscle, so pair any deficit with 1.6–2.2 g of protein per kg.
Is Mifflin better than Harris-Benedict?
Yes — it is more accurate in validation studies and needs fewer inputs.
Should I eat back exercise calories?
No, the multiplier already includes activity.
How many calories to lose 1 kg?
About 7,700 kcal, which is why a 500 kcal daily deficit takes roughly two weeks.
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