Weight Loss Calculator

Find the daily calorie deficit you need to reach your goal weight by a target date, based on ~3,500 kcal per pound (~7,700 kcal per kg) of body fat.

Quick Facts

Method
~3,500 kcal per pound of fat (~7,700 kcal per kg)
Total deficit ÷ days gives the daily calorie deficit needed.

Your Results

Calculated
Daily calorie deficit
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Eat/burn this much less per day
Total to lose
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Current minus goal weight
Weekly rate
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Average loss per week
Total calorie deficit
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Over the full timeframe

Ready

Enter your current weight, goal weight, and timeframe, then calculate.

About the Weight Loss Calculator

This calculator turns a weight goal into a daily target. You enter your current weight, your goal weight, and how many weeks you want to take, and it works out the calorie deficit you need to run each day to get there. It is a planning tool built on the energy-balance principle: to lose stored body fat, you have to take in fewer calories than you burn, and the size of that gap over time determines how fast the weight comes off.

The formula

The math rests on one well-established figure: about 3,500 kcal are stored in one pound of body fat, or roughly 7,700 kcal per kilogram. The steps are:

Weight to lose = current weight − goal weight.
Total calorie deficit = weight to lose × 3,500 (per lb) or × 7,700 (per kg).
Daily deficit = total calorie deficit ÷ (weeks × 7 days).

For example, to lose 20 lb in 20 weeks: 20 × 3,500 = 70,000 kcal total, spread over 140 days = 500 kcal per day. That happens to be the classic "1 pound per week" target.

Where the 3,500 number comes from

Pure fat yields about 9 kcal per gram. Body-fat (adipose) tissue is not pure fat — it is roughly 87% fat by mass, with the rest water and protein. So one pound (454 g) of adipose tissue holds about 454 × 0.87 × 9 ≈ 3,555 kcal, which is conventionally rounded to 3,500. This is often called the Wishnofsky rule, after the 1958 paper that popularized it.

Common reference points

A 500 kcal/day deficit ≈ 1 lb (0.45 kg) lost per week. A 1,000 kcal/day deficit ≈ 2 lb (0.9 kg) per week, which is the usual upper limit health authorities recommend. A deficit of 250 kcal/day (skip one sugary drink and a snack) ≈ 0.5 lb per week. These benchmarks let you sanity-check any plan at a glance.

Deficit vs. eating less

The "deficit" is the gap between calories in and calories out, so you can create it by eating less, moving more, or both. Splitting a 500 kcal/day target into 300 kcal eaten less and 200 kcal burned through exercise is usually more sustainable than diet alone, and physical activity helps preserve muscle while you lose fat.

Frequently Asked Questions

How many calories is one pound of body fat?
About 3,500 kcal per pound, or roughly 7,700 kcal per kilogram. Fat stores about 9 kcal per gram, and adipose tissue is around 87% fat by mass, so a pound (454 g) of it holds about 454 × 0.87 × 9 ≈ 3,500 kcal. To lose a pound of fat you need a cumulative deficit of roughly that size.
What is a safe rate of weight loss?
Most guidelines recommend about 1 to 2 lb (0.5 to 1 kg) per week. That maps to a 500 kcal/day deficit for 1 lb/week and a 1,000 kcal/day deficit for 2 lb/week. Faster loss risks muscle loss and rebound; if your timeframe demands a deficit above roughly 1,000 kcal/day, extend the timeline or consult a professional.
Why does real weight loss slow down over time?
The 3,500-kcal rule assumes a constant deficit produces constant loss, but as you get lighter your body burns fewer calories at rest and during activity (a smaller body costs less to move). So a fixed daily calorie intake yields a shrinking deficit, and loss tapers. Treat this calculator's output as an initial target and recalculate as your weight drops.

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