Not medical advice.These estimates are for general informational use only and aren't a substitute for professional medical advice, diagnosis, or treatment. Consult a qualified healthcare provider before changing your diet, exercise, or medication.

The 7,700 kcal-per-kilogram energy balance

Body weight follows the first law of thermodynamics: when the energy you eat is less than the energy you burn, the shortfall is made up mostly from stored fat. Stored body fat holds roughly7,700 kcal per kilogram (about 3,500 kcal per pound). So a sustained deficit of, say, 500 kcal/day removes about 500 ÷ 7,700 ≈ 0.065 kg of tissue per day, or around half a kilogram a week. This projection accumulates that daily change to draw your weight curve. The energy-density figure traces back to Max Wishnofsky's 1958 analysis in theAmerican Journal of Clinical Nutrition.

Why the curve flattens — metabolic adaptation

A common mistake is to assume weight loss is a straight line. It is not. The energy you burn at rest — your basal metabolic rate — depends on how much you weigh. As you get lighter, you burn fewer calories doing the same things, so your total daily energy expenditure (TDEE) falls. A deficit that started at 500 kcal/day quietly shrinks toward zero as your body gets smaller, and weight loss slows to a crawl as you approach a new maintenance point. This ismetabolic adaptation, and it is why the projected line bends and flattens rather than continuing straight down.

To capture this, the model recomputes your TDEE every simulated day from your current weight, rather than using a single fixed number. Resting metabolism is estimated with theMifflin-St Jeor equation (Mifflin MD, St Jeor ST, et al.,American Journal of Clinical Nutrition, 1990), the formula most validated for the general population, and scaled by a standard activity multiplier (1.2 sedentary to 1.9 very active) in the Harris-Benedict tradition.

How to read the result

Enter your details and either a daily calorie deficit or an absolute daily intake. The tool reports an estimated goal date (today plus the projected number of days) and weeks-to-goal, and draws the day-by-day curve. The healthy-BMI reference range and the daily deficit shown are computed from your inputs; nothing you enter is stored or sent anywhere — all calculation happens in your browser.

Safety limits built in

These projections are estimates for planning, not a prescription. The tool will not chart a plan that implies eating under about 1,200 kcal/day, an intake widely considered unsafe without medical supervision, nor a goal weight below aBMI of 18.5 (the WHO underweight threshold); in those cases it shows your healthy weight range and support resources instead.

Frequently asked questions

Why is my projected timeline longer than a simple calculator's?

Simple calculators usually divide the total weight to lose by a fixed weekly rate, which assumes your deficit never changes. In reality your maintenance calories drop as you get lighter, so a fixed intake produces an ever-smaller deficit and a longer, flattening curve. This model accounts for that, which is more realistic — if less flattering — than a straight line.

Should I just create a bigger deficit to finish faster?

Not necessarily. Larger deficits are harder to sustain and this tool deliberately will not chart plans implying very low intakes (under roughly 1,200 kcal/day) or underweight goals. A moderate, consistent deficit that you can actually maintain usually beats an aggressive one you abandon. If food, weight, or eating is causing you distress, support is available: in the US you can reach the NEDA Helpline at 1-800-931-2237, or call or text988 at any time.

How accurate is the goal date?

Treat it as a planning estimate, not a promise. The energy-balance model is a good approximation, but real weight changes day to day with water, sodium, glycogen, digestion, sleep and hormones, and individual metabolisms differ. Use the curve to set expectations and track your real trend over time rather than judging progress by any single weigh-in.

Is my data saved or uploaded?

No. Everything is computed in your browser and nothing you enter leaves your device or is sent to a server.