Weight Loss Calculator

This calculator works out the daily calorie deficit needed to reach your target weight by a chosen date. One kilogram of body fat stores approximately 7,700 kcal, so a deficit of 500 kcal per day produces roughly 0.5 kg of weight loss per week. The NHS recommends a safe rate of 0.5 to 1.0 kg per week, which amounts to a weekly deficit of 3,500 to 7,700 kcal, or 500 to 1,100 kcal a day.

Behind that deficit sits an estimate of what you burn. The Mifflin-St Jeor equation gives basal metabolic rate, the energy you use simply existing, as 10 times weight plus 6.25 times height minus 5 times age plus 5 for men, and the same sum minus 161 for women. A 30-year-old woman of 70 kg and 165 cm comes out at 1,401 kcal. Multiplying by an activity factor turns that into total daily energy expenditure, using 1.2 for sedentary, 1.375 for lightly active, 1.55 for moderately active and 1.725 for very active, which places the same woman somewhere between 1,680 and 1,960 kcal.

Most people overstate how active they are, so office workers are usually better served by a factor of 1.2 to 1.4 and those in hands-on jobs by 1.5 to 1.7. Having estimated expenditure, the calculator subtracts the daily deficit your deadline demands, then flags any target needing more than 1,000 kcal a day, or an intake below 1,200 kcal for women or 1,500 kcal for men, because figures like those are rarely sustainable. Calorie counting is accurate only to within 15 to 20% even with kitchen scales, so erring slightly high on intake is the safer mistake.

Enter your current weight, target weight, goal date and activity level to see daily calories, the expected weekly loss rate and whether the timeline is realistic. Extending the deadline by a few weeks can often make the difference between a healthy deficit and an extreme one. A 75 kg moderately active woman with an expenditure of about 2,000 kcal who eats 1,500 kcal is running a 500 kcal deficit and can expect around 0.5 kg a week. Pushing to a 2,000 kcal deficit works for four to eight weeks at most before adaptation, muscle loss and a plateau catch up with it.

Very low intakes prompt the body to defend itself within two to four weeks. Thyroid output shifts down, and non-exercise activity thermogenesis, the fidgeting and incidental movement you do without thinking, falls by 200 to 400 kcal a day. Lost muscle lowers the floor further, since each kilogram accounts for about 13 kcal a day at rest. Four to six weeks in, the scale stops moving on exactly the same intake. A moderate deficit of 500 to 700 kcal a day, with a refeed at maintenance every week or two, keeps that spiral at bay.

Protein decides whether the weight you lose is fat or muscle. Aim for 1.6 to 2.2 g per kg of bodyweight, which comes to 112 to 154 g a day at 70 kg. Fall short and 30 to 50% of the loss can come from muscle, the outcome nobody wants. Protein also keeps you full for longer and costs more to digest, with 25 to 30% of its calories used up in digestion against 5 to 10% for carbohydrate and fat. Chicken supplies 31 g per 100 g, eggs 13 g, Greek yoghurt 10 g, cooked lentils 9 g, and a scoop of whey powder 20 to 25 g.

What surrounds the diet matters as much as the diet. Strength training two or three times a week preserves muscle and props up your metabolic rate over the long run, while cardio adds to expenditure without changing body composition by itself. Sleeping seven to nine hours protects the result, and under six hours works against it by raising cortisol and disrupting hunger hormones. Walking 8,000 to 10,000 steps a day is worth another 200 to 400 kcal. A two-week diet break at maintenance every eight to twelve weeks heads off adaptation before it bites. The long-run numbers explain why the framing matters: about 95% of dieters regain within five years, against 20% of people who changed how they live.