Why the same calorie target works differently for two people
Two people, same height and weight, same target — and very different results. Here's what the calculator can't see.
3 min readReviewed May 1, 2026
Quick answer
Equations like Mifflin–St Jeor are population averages. Real BMR can vary by 10–15% in either direction at the same height, weight, age, and sex.
Real-world variation comes from
- Lean mass differences — more muscle = higher BMR.
- NEAT — some people fidget hundreds of extra calories per day.
- Sleep, stress, and hormones (especially thyroid).
- Tracking accuracy — most people under-report intake.