How does calories in vs out affect weight?

Eating fewer calories than you burn creates a deficit and leads to weight loss; eating more creates a surplus and leads to gain. About 7700 kcal equals roughly 1 kg of body weight.

Why doesn't my real weight match the estimate?

Short-term weight swings come from water, glycogen and digestion. The estimate reflects the underlying fat trend over weeks, not day-to-day scale numbers.

How big a deficit is safe for losing weight?

A daily deficit of about 500 kcal — roughly 0.45 kg (1 lb) per week — is a widely used, sustainable target. Larger deficits lose weight faster but are harder to maintain and can cost muscle.

How many calories are in 1 kg or 1 lb of body weight?

This tool uses about 7,700 kcal per kilogram, which is equivalent to roughly 3,500 kcal per pound. Those figures are what convert your weekly calorie balance into an estimated weight change.

Is this medical advice?

No. It is an educational estimate. For a personalised plan, speak to a doctor or registered dietitian.

Calories In vs Out Calculator

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.

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.