Weight Loss Calculator

Two compounding reasons. (1) Mass effect: a 90-kg body burns more calories than a 80-kg body just doing nothing — fewer kilos means lower BMR. (2) Metabolic adaptation (adaptive thermogenesis): after weeks in a deficit, your body downregulates non-essential energy use. Thyroid hormone (T3) drops 5-15%, NEAT (fidgeting, posture, spontaneous movement) drops, and TDEE can fall 10-25% below predicted. This calculator's week-by-week simulation captures the mass effect; expect adherence to add another 1-3 weeks to the timeline at the back end.

Three failure modes. (1) Adaptive thermogenesis hits hardest with severe deficits — your TDEE crashes faster than the math predicts. (2) Muscle loss at very low calories means a lower BMR permanently unless you regain that muscle. (3) Hunger hormones — leptin plummets and ghrelin spikes, and they stay altered for months after you stop dieting (the famous Biggest Loser study found persistent hormone changes 6 years post-show). The result: rebound weight gain, often above starting weight, plus less muscle than before.

Yes, but for the right reasons. Cardio adds to your weekly calorie burn (a 30-min jog ≈ 250-350 kcal), which can speed up loss or let you eat more. Resistance training is more important: it preserves muscle during the deficit, which keeps your BMR higher and prevents you from ending up "skinny-fat". Aim for 3 strength sessions/week + 8-12K daily steps. Don't try to "out-exercise" a bad diet — calorie burn from exercise is often less than expected, and hunger compensates.

Possible short-term, but rarely recommended. Rule of thumb: keep deficit under 25% of your TDEE. A 90-kg sedentary person with a 2400-kcal TDEE shouldn't go below ~1800 kcal/day. Below that, you risk: rapid muscle loss, micronutrient deficiencies, fatigue that wrecks workout quality, gallstones (low-fat very-low-calorie diets), hormonal disruption (especially in women — irregular cycles, low energy), and dramatically slower long-term metabolism. If you're obese (BMI 35+) under medical supervision, larger deficits can be appropriate — but that's a doctor-supervised protocol, not a self-prescribed one.

Most people do — about 80% of dieters regain within 2 years if they treat the diet as temporary. The fix isn't a better diet; it's a permanent shift in eating and activity habits. Tactics that work: (1) After hitting goal, transition to maintenance calories slowly over 4-8 weeks (reverse diet) so your TDEE recovers. (2) Keep tracking 1-2 days/week as a check-in. (3) Stay strong (lift weights) and walk daily — muscle and movement are your best metabolic insurance. (4) Weigh weekly; if you're up 2 kg from goal for 2+ weeks, course-correct immediately rather than waiting for 9.