Why diets stall
You cut calories, drop weight fast for a few weeks — and then the scale slows down, even though you're eating the same. That is not a lack of discipline or a "broken metabolism". It's math: your daily burn depends on your weight, so losing weight shrinks your own deficit. Let's watch it happen.
1. How much of your burn comes from the gym?
A 30-year-old man, 176 lb (80 kg), 5'10", who trains 4× a week. Of all the calories he burns in a day, what percentage comes from exercise?
- BMR — 65% · what your body spends just existing: heart, brain, breathing, temperature
- NEAT — 18% · non-exercise movement: walking, stairs, fidgeting, standing
- TEF — 10% · the energy used to digest your food
- Exercise — 7% · yes, that's all
The practical lesson: you can't outrun your fork. Those ~200 kcal/day of training vanish in one snack. A fast-food combo (~1,100 kcal) would take roughly 110 minutes of running to offset. That doesn't make training useless — it means exercise is terrible as a calorie eraser and excellent for everything else: cardiovascular health, holding on to muscle while you diet, and raising your NEAT.
2. Your numbers
The Mifflin-St Jeor equation is the best-validated way to estimate resting metabolism: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + s (s = +5 male, −161 female). Multiply by your activity factor and you get TDEE — your total daily burn, which is your maintenance level.
When torn between two activity levels, pick the lower one — nearly everyone overestimates their own activity, and it's the #1 reason behind "I barely eat and still don't lose weight".
3. The plateau: simple math lies
The classic rule says 1 lb of fat stores ~3,500 kcal, so a 500 kcal/day deficit should give ~1 lb a week forever. But as you lose weight you carry less of it — and a smaller body burns less. The deficit shrinks on its own.
Chart comparing the linear weight-loss projection with the physiological projection over one year.
The common mistake is cutting food further and further. Since your burn fell too, you spiral into unsustainable restriction. The honest fixes: recalculate your target every 10 lb lost, raise your NEAT (walking more is the biggest controllable burn outside of basal), protect muscle with strength training and adequate protein — lean mass is what holds your BMR up — and accept that a slower pace is not failure: it's expected.
Calculate your target
The full calculators include activity factors, macros and the step-by-step math.
Open the Calorie Deficit Calculator →See also: BMR & TDEE · Macros · Daily protein · BMI
This is educational content, not medical advice. Estimates use the Mifflin-St Jeor equation (Am J Clin Nutr, 1990), conventional activity factors and the ~3,500 kcal per pound of fat reference. Every model is an average: real burn varies ±10% or more between people, and the breakdown in section 1 is an illustrative decomposition. Rapid weight loss, intakes below ~1,200 kcal/day (women) or ~1,500 kcal/day (men), pregnancy, medication use or metabolic conditions call for a doctor or registered dietitian.