Weight change comes down to energy balance — the calories you eat versus the calories you burn. This calculator takes your daily intake and daily expenditure and shows your deficit or surplus, the weekly calorie total, and an estimated weekly weight change. It also flags whether that change actually matches your stated goal of losing or gaining weight, so you can sanity-check your plan in seconds.
How it works
The daily net is simply calories in − calories out. A negative net is a deficit (weight loss); a positive net is a surplus (gain). The weekly total is the daily net × 7. To turn calories into weight, the tool divides the weekly calorie balance by the energy stored in body tissue:
1 kg ≈ 7,700 kcal · 1 lb ≈ 3,500 kcal
If you choose pounds, it uses 7,700 × 0.453592 ≈ 3,492 kcal per pound. The result is signed, so a deficit shows as weight lost and a surplus as weight gained.
Worked example
You eat 2,000 kcal and burn 2,400 kcal per day, aiming to lose weight (kg):
| Step | Calculation | Result |
|---|---|---|
| Daily net | 2,000 − 2,400 | −400 kcal (deficit) |
| Weekly total | −400 × 7 | −2,800 kcal |
| Weekly weight | −2,800 ÷ 7,700 | ≈ −0.36 kg |
You are in a deficit that aligns with a weight-loss goal, projecting about 0.36 kg lost per week.
Short-term scale swings come from water and food in transit; the estimate reflects the fat trend over weeks. Everything runs in your browser, privately.
How this differs from the calorie deficit calculator
This tool is simpler and more direct. You supply both numbers — calories in and calories out — and it shows the balance. The calorie deficit calculator estimates your calories-out figure (TDEE) from your height, weight, age, and activity level using the Mifflin-St Jeor equation, then computes a daily target to hit a chosen rate of loss.
Use this tool when you already know (or have measured) your calorie expenditure — for example, from a fitness tracker or heart-rate monitor. Use the deficit calculator when you need the expenditure side estimated from your body stats.
Common uses
Tracking a diet day by day. Enter what you ate and what your tracker says you burned. The weekly summary tells you whether the week’s balance puts you on course for your goal.
Evaluating a new exercise routine. If you add a workout that burns an extra 300 kcal three days a week, you can see exactly how many extra weekly calories that represents and what weight change it projects over a month, assuming intake stays the same.
Checking a planned surplus for muscle gain. Muscle building typically requires a small calorie surplus — often 200–500 kcal/day. Enter a target intake above your expenditure and verify the surplus is in a sensible range before starting.
Why the scale doesn’t always agree
The formula predicts fat gain or loss; the scale measures everything — fat, muscle, water, digestive contents, and glycogen stores. A single day of high carbohydrate intake can add a kilogram of water weight as glycogen is stored; a day of low carbohydrate intake or extra sweating can subtract it. The estimate here reflects the underlying trend over weeks, not the day-to-day number on the scale. Tracking weekly averages rather than daily weigh-ins reduces the noise considerably.