Chapter 01 · The math
How energy balance works
A sustained deficit causes weight loss; a surplus causes gain. The 3,500 kcal per pound rule is a first approximation, useful for setting a starting target.3 A more complete dynamic model adds adaptive thermogenesis: your TDEE drops over time beyond what mass loss alone explains, which is why predicted and actual loss diverge after the first month.2
*12 month plan, billed once for the term when a physician approves. Renews each term.
| Daily deficit | Approximate weekly loss | Who it suits |
|---|---|---|
| 250 kcal | about 0.5 lb | Lean, slow and steady |
| 500 kcal | about 1 lb | Most adults |
| 750 kcal | about 1.5 lb | More to lose |
| 1,000 kcal | about 2 lb | Physician supervision only |
Deficits above 1,000 kcal per day belong under medical oversight.
Chapter 02 · The limits
What a safe deficit looks like
500 kcal per day produces about a pound per week for most adults. 750 kcal per day works for people with more to lose. Over 1,000 kcal per day requires physician oversight, because aggressive deficits carry real risks: muscle loss, gallstones, hair shedding, and faster metabolic adaptation. The calculator floors your target at 1,200 kcal for that reason.
Start here · one question
What's your goal weight?
Choose a goal to discuss with your clinician. You can change it in your intake.
The point: bigger deficits do not mean better results. Sustainable beats aggressive almost every time. Individual results vary.
Chapter 03 · The other direction
Gaining muscle instead
To gain muscle, run a 250 to 500 kcal per day surplus above TDEE paired with resistance training. Bigger surpluses add fat rather than muscle, since roughly a pound per week is the upper conversion rate. The calculator caps a gain surplus at 500 kcal for the same reason. If you are using a GLP-1 medication or have a medical condition, a licensed physician, not this calculator, sets the right target. Individual results vary.
