How the weight loss curve is calculated
Energy stored equals intake minus expenditure. Expenditure is resting metabolism from the Livingston–Kohlstadt equation, movement that scales with body weight, about 7.5% of intake spent digesting food, and spontaneous activity that falls when you eat less. Fat and lean tissue change together along a Forbes curve. Fat stores about 9,500 kcal per kilogram. Lean tissue stores about 1,020.
The starting intake is the Institute of Medicine estimate for an active adult who is weight-stable: usual daily life plus about an hour of movement. It uses age, height, sex, and weight. The projection then holds your chosen deficit constant for up to three years and records weight at the end of each week.
A flat rule of 7,700 kcal per kilogram draws a straight line. This curve bends, because a lighter body burns fewer calories. The resting-metabolism piece of that bend is small. The larger piece is simply weighing less.
FAQ
How is the current calorie intake calculated?
The number assumes you are weight-stable: not already losing or gaining. It uses the Institute of Medicine equation for an active adult, from age, height, sex, and weight. Active here means usual daily life plus about an hour of movement. Equations of this kind, fit to doubly labeled water studies, explain about 60% of the difference in intake from one person to the next. The rest is training beyond that, a physical job, and ordinary day-to-day weight swings.
The intake at the top of the result looks higher than what I eat. Why?
The formula was fit to a large group that varied in age, sex, height, and weight. It still leaves about 40% of the variation unexplained. Routine movement and weeks when your weight is not actually stable are the usual reasons a personal number sits below the estimate. A clinic measurement would tighten it. Treat this figure as the model’s starting intake, then check it against two or three weeks on the scale.
Does the calculator include metabolism slowing during weight loss?
Yes. While you are in a deficit the model lowers resting metabolism by 2%, and expenditure also falls because a lighter body costs less to carry. In trials, the pure metabolic-adaptation piece is modest, often about 50 to 100 kcal per day. Most of the bend in the curve is the smaller body, not a stalled metabolism.
If the missing weight loss is not my metabolism, why is the scale stuck?
Adherence, food that never gets logged, medications, and medical conditions sit outside what age, height, sex, and weight can predict. If a month of honest intake does not follow the curve, talk with your clinician about the pattern. The model cannot see those factors.
If I burn more through exercise, do I just eat it back and lose nothing?
An energy-balance analysis asked why people lose less than the calories of a set exercise dose. Vigorous exercise tended to raise how much people ate. When intake was held constant, metabolism did slow. The same work found that aerobic exercise spares lean tissue: weight lost is mostly fat, and weight gained while training is mostly lean. This page projects a diet change only. It does not add a new training plan.
Related calculators
Sources: Thomas et al., Journal of Biological Dynamics, 2011; Livingston and Kohlstadt, Obesity Research, 2005; Forbes, Nutrition Reviews, 1987; Institute of Medicine energy requirement equations, 2005; Martin et al., Obesity, 2007; Thomas et al., Obesity Reviews, 2012.
Disclaimer: An estimate, not a prescription. The curve does not know your training, medications, or whether the deficit is actually kept. Intakes under about 1,200 kcal for women or 1,500 kcal for men need clinical supervision. Talk with a qualified professional before a large deficit.
