What is the calories-per-pound-of-fat rule?
A long-standing nutrition rule of thumb states that one pound of stored body fat holds approximately 3,500 calories of energy. To lose that pound, you must create an equal calorie deficit — either by eating less, moving more, or a combination of both. This calculator multiplies the pounds you want to lose by 3,500 to estimate the total deficit, then divides by your chosen timeframe to show the daily deficit you would need to maintain.
How to use it
Enter the number of pounds of fat you want to lose. Optionally, enter a timeframe in days to see the daily calorie deficit required to hit that goal. Leave the timeframe blank (or zero) if you only want the total.
The formula explained
The math is simple: $$\text{Total Deficit} = \text{Pounds of fat} \times 3500$$ For the daily figure we divide that total by the number of days: $$\text{Daily Deficit} = \frac{\text{Pounds of fat} \times 3500}{\text{Days}}$$ A 500-calorie daily deficit, for example, theoretically yields about one pound of fat loss per week (\(500 \times 7 = 3500\)).
Worked example
Suppose you want to lose 10 pounds over 30 days. $$\text{Total deficit} = 10 \times 3500 = 35{,}000 \text{ calories}$$ $$\text{Daily deficit} = 35{,}000 \div 30 \approx 1{,}167 \text{ calories per day}$$ That is an aggressive target, so most experts recommend a slower, more sustainable pace.
FAQ
Is the 3,500-calorie rule exact? No. It is a useful approximation. Real fat loss varies with metabolism, water weight, and muscle changes, and the body adapts over time, so actual results differ.
How fast should I lose weight? Most guidelines suggest 0.5–2 pounds per week, which means a daily deficit of roughly 250–1,000 calories.
Can I create the deficit through exercise alone? You can, but combining moderate diet changes with activity is usually easier to sustain than relying on exercise only.
