Weight Loss Calculator
Estimate the time needed to reach your weight goal based on your daily calorie deficit. Week-by-week projection.
Everything you need to know about weight loss and calorie deficit
Why use a weight loss calculator?
Weight loss comes down to one principle: a calorie deficit. But without a proper tool, it's hard to estimate how long it will take to reach your goal. This calculator gives you a realistic week-by-week projection that accounts for the gradual decline in your TDEE.
Unlike linear estimates, our tool recalculates your metabolism each week as your weight drops. This reflects the real-world phenomenon where weight loss naturally slows over time, since a lighter body burns fewer calories.
Seeing your progression curve and the number of weeks required helps you stay motivated, adjust your deficit when needed, and avoid the unrealistic expectations that lead to quitting.
Who uses this weight loss calculator?
- People starting a diet
- Before beginning, it's essential to know how long the transformation will take. This calculator sets realistic expectations and helps choose a sustainable deficit (300-500 kcal) rather than a crash diet destined to fail.
- Fitness coaches and personal trainers
- Fitness professionals use this type of tool to plan their clients' cutting phases with precise timelines, while ensuring the rate of loss stays healthy (max 1 kg/week).
- Athletes preparing for competition
- Athletes often need to hit a weight class by a specific date. The week-by-week projection allows them to plan their weight cut without compromising performance or health.
- People under professional medical guidance
- As a complement to medical or dietary supervision, this tool helps visualize the impact of a given calorie deficit and discuss adjustments with your practitioner based on clear data.
How does the calculator work?
Enter your profile (sex, age, height, current weight, target weight), your physical activity level, and your desired daily calorie deficit. The calculator uses the Mifflin-St Jeor formula to estimate your BMR.
Each week, TDEE is recalculated based on your new estimated weight. The deficit is applied using 7,700 kcal per kilogram of body fat, which produces a progressive and realistic projection.
You get a visual progression curve, a week-by-week table showing estimated weight, kilograms lost, and recalculated TDEE, plus a safety indicator if the rate of loss exceeds 1 kg per week.
Frequently asked questions about weight loss
- What calorie deficit should I choose to lose weight?
- A deficit of 300 to 500 kcal per day is generally recommended. This corresponds to losing about 0.3 to 0.5 kg per week, a rate considered safe and sustainable. A deficit above 750 kcal increases the risk of muscle loss and nutritional deficiencies.
- Why does weight loss slow down over time?
- As you lose weight, your body needs less energy to function (lower BMR). Your TDEE therefore decreases, and the same calorie deficit produces slower loss. This is a normal physiological phenomenon called metabolic adaptation.
- How many calories are in 1 kg of body fat?
- One kilogram of adipose tissue contains approximately 7,700 kcal of stored energy. This value serves as the basis for the calculation: to lose 1 kg, you need to create a cumulative deficit of roughly 7,700 kcal.
- Is it dangerous to lose more than 1 kg per week?
- Losing more than 1 kg per week over an extended period is not recommended. It increases the risk of muscle wasting, chronic fatigue, nutritional deficiencies, and metabolic slowdown. Rapid losses are also associated with higher rates of weight regain.
- Does physical activity level significantly affect the result?
- Yes, significantly. The activity multiplier scales your BMR by a factor ranging from 1.2 (sedentary) to 1.9 (very active). An active person has a higher TDEE, meaning they can eat more while maintaining the same deficit, or lose weight faster at the same intake.