Calorie Deficit Calculator & Goal Date Planner

First your resting energy use (BMR) is calculated with the Mifflin-St Jeor equation: 10 × weight in kg + 6.25 × height in cm − 5 × age, plus 5 for men or minus 161 for women. That is multiplied by your activity level (1.2 for sedentary up to 1.9 for extra active) to give your TDEE, the calories you use in a day. For weight loss the calculator subtracts 250, 500 or 750 kcal depending on the pace you choose, but never suggests less than 1,200 kcal a day for women or 1,500 kcal for men.

For most adults a deficit of 250–500 kcal a day, losing roughly 0.25–0.5 kg (0.5–1 lb) a week, is sustainable and protects muscle. Larger deficits can be used for a short time by people with more weight to lose, but very low intakes leave little room for protein, vitamins and minerals. That's why JaxFit never suggests going below 1,200 kcal a day for women or 1,500 kcal for men, and doesn't offer weight-loss targets to under-18s or anyone underweight.

The calculator simulates your progress day by day. Each day it works out your energy use at your projected weight, applies your chosen deficit (never going below the safe minimum intake) and counts about 7,700 kcal for each kilogram of body fat. As you get lighter you use a little less energy, so progress slows gently near the goal. Real weight also moves with water, salt and hormones, so treat the date as a friendly milestone, not a deadline.

The World Health Organization classifies adult BMI (weight in kg divided by height in metres squared) as: below 18.5 underweight, 18.5 to 24.9 healthy weight, 25.0 to 29.9 overweight, and 30.0 or above obesity. BMI is a quick screening number, not a diagnosis: it doesn't measure body fat directly, so very muscular people can score high. For under-18s, BMI must be compared with growth charts for age and sex instead of these adult categories.

Both are daily time-restricted eating plans. On 16:8 you fast for 16 hours and eat within an 8-hour window, for example noon to 8 PM. On 18:6 you fast for 18 hours and eat within 6 hours, for example 2 PM to 8 PM. 16:8 is the most popular starting point because it mostly uses the hours you are asleep. 18:6 adds two more hours in the fat-burning stage, but it is harder to keep up, so most people build up to it gradually from 14:10 or 16:8.

Yes. Every calculation runs in your own browser. Your age, weight, goals, fasting timer and Habit Garden are saved only in your browser's local storage on this device, so they're there when you come back. Nothing is uploaded, there are no accounts, no analytics cookies, no tracking scripts and no ads. Clearing your browser data removes everything.