What This Calculator Does
This tool estimates how much body fat you can expect to lose from a sustained calorie deficit. It uses the widely cited rule that roughly 3,500 calories are stored in one pound of body fat. By entering your average daily calorie deficit and how many days you maintain it, the calculator multiplies the two to get a total deficit and divides by 3,500 to estimate pounds lost.
How to Use It
Enter your daily calorie deficit — the number of calories you burn beyond what you eat each day (for example, eating 500 kcal less than your maintenance needs). Then enter the number of days you plan to keep that deficit. The result shows your estimated fat loss in pounds, along with the total accumulated deficit.
The Formula Explained
The calculation is simple:
$$\text{Pounds} = \frac{\text{Daily Deficit} \times \text{Days}}{3{,}500}$$The 3,500 figure is the classic Wishnofsky estimate for the energy content of a pound of fat. A consistent 500 kcal daily deficit therefore equals about 1 pound per week (\(500 \times 7 = 3{,}500\)).
Worked Example
Suppose you maintain a 500 kcal daily deficit for 30 days. Total deficit = \(500 \times 30 = 15{,}000\) kcal. Pounds lost = \(15{,}000 \div 3{,}500 \approx 4.29\) pounds over the month.
FAQ
Is the 3,500-calorie rule exact? No. It's a useful approximation. Real-world weight loss slows over time as metabolism adapts and water weight fluctuates, so treat the result as an estimate rather than a guarantee.
Does this include water weight? No, it estimates fat loss only. Early weight loss often includes water and glycogen, which can make the scale move faster at first.
What's a safe deficit? A deficit of 500–1,000 kcal/day (about 1–2 lb/week) is commonly considered safe and sustainable for most adults. Consult a healthcare professional for personalized advice.
