Every plateau you've ever hit has a single explanation: your TDEE dropped with your body weight, and your old deficit isn't a deficit anymore. Here's the math and how to plan around it.
The arithmetic of a shrinking body
TDEE has two size-dependent components. BMR scales with body mass — Mifflin-St Jeor gives 10 calories per kg of body weight as the dominant term. So losing 10 kg (22 lbs) drops BMR by ~100 calories. Activity calories also drop, because you're moving less mass the same distance — a 200 lb person burns more running a mile than a 180 lb person does.
The rule of thumb: expect TDEE to drop by about 5–10 calories per pound lost. A 30 lb loss lowers TDEE by 150–300 calories per day. That matches the plateau experience — the deficit that used to be 500 calories (producing 1 lb/week of loss) becomes 200–350 calories (producing 0.4–0.7 lb/week).
Metabolic adaptation on top
Beyond the pure size-adjustment, extended dieting triggers adaptive thermogenesis — your body defending against famine by becoming more efficient. Measured declines in BMR beyond what size would predict range from small (2–5% on sustainable cuts) to large (15–25% on extreme or prolonged cuts — the Biggest Loser contestants famously showed 500+ calorie drops).
For most people losing weight at a sensible pace, adaptation is in the small camp. For aggressive or extended cuts, it compounds and makes further loss harder.
The break-the-plateau playbook
When the scale stalls for 2+ weeks:
- Recalculate TDEE at your current weight. Update your calorie target.
- Drop calories by ~10% (150–250). Keep protein constant; cut from fat and carbs.
- Audit activity honestly. Chronic dieters unconsciously move less (lower NEAT). Are your steps really the same?
- Consider a diet break. 1–2 weeks eating at new-maintenance every 8–12 weeks can reset adaptation markers.
The long-view strategy
Don't expect to diet down from start to finish in one continuous push. For losses of 30+ lbs, plan for multiple phases: cut for 8–12 weeks, maintain for 2, cut again. The total timeline is longer but the total weight lost is usually higher because adaptation doesn't compound as badly.
And recalculate often. The number you started at isn't the number you're working with three months later. Every 10–15 lbs, run the math again.
Update age, weight, and activity. Get the number that matches the body you have now.