TDEE Calculator — with metabolic adaptation

Why TDEE calculators are usually wrong for repeat dieters

The Mifflin-St Jeor equation predicts BMR for the average adult — and it's accurate to within ±10% for most people who've never dieted. But adults who've been through multiple weight-loss cycles carry residual metabolic adaptation — measurably lower energy expenditure than their body composition would predict.

The Fothergill 2016 Biggest Loser study¹Obesity · 2016Fothergill E et al. — Persistent metabolic adaptation 6 years after 'The Biggest Loser' competition documented that ex-contestants' resting metabolic rate remained ~500 kcal/day below predicted six years after the show, even as most regained weight. Rosenbaum and Leibel²International Journal of Obesity · 2010Rosenbaum M, Leibel RL — Adaptive thermogenesis in humans have characterized this adaptive thermogenesis as a 5–15% reduction in expenditure beyond what mass change alone would explain — driven by leptin drop, sympathetic-nervous suppression, lower thyroid output, and more efficient skeletal muscle. Müller and Bosy-Westphal's reviews³Obesity · 2013Müller MJ, Bosy-Westphal A — Adaptive thermogenesis with weight loss in humans quantify the effect more conservatively, but agree on direction. Trexler's⁴Journal of the International Society of Sports Nutrition · 2014Trexler ET, Smith-Ryan AE, Norton LE — Metabolic adaptation to weight loss: implications for the athlete athlete review describes the same phenomenon in lean dieters.

How to refine the estimate

The single most accurate way to know your TDEE is to track for 2 weeks at a fixed intake. If your weight is stable across two weeks, you found maintenance. If you're losing 0.25–0.5 kg/week, that intake is your fat-loss target. If you're unexpectedly losing or gaining more than that, adjust by ~150 kcal and watch another two weeks. The calculator's number is the starting point; the scale and tape measure refine it.

When to consult a metabolic-rate test

For adults with deep metabolic adaptation history (severe yo-yo dieting, long GLP-1 use ending, post-bariatric maintenance), an indirect-calorimetry test (RMR measurement) provides a much better estimate than any equation. Most performance and metabolic clinics offer it for $100–250. Worth doing once if your calculated TDEE consistently overestimates your real intake.