Losing weight safely requires a realistic plan built around a sustainable calorie deficit. This free online weight loss calculator works out how much weight you need to lose, your weekly rate of loss, and the daily calorie deficit required to hit your goal weight within your chosen time frame. It also flags overly aggressive plans so you can adjust your timeline for safer results.
Find out how much of a daily calorie deficit you need to reach your goal weight in your chosen time frame.
The 7,700 kcal figure is the approximate energy stored in one kilogram of body fat. The daily deficit is how many fewer calories than you burn you would need to eat each day, or burn through extra activity, to lose that fat in the time you set. A warning appears when the weekly rate is above 1 kg.
Someone weighing 85 kg wants to reach 75 kg in 20 weeks. That is 10 kg to lose at 10 ÷ 20 = 0.50 kg a week. The daily deficit is 10 × 7,700 ÷ 140 days = 550 kcal. If their maintenance needs are around 2,300 kcal, they would aim to eat roughly 1,750 kcal a day, or eat a little more and add a daily walk.
Squeeze the same 10 kg into 8 weeks and the numbers become 1.25 kg a week and a 1,375 kcal daily deficit. For most people that would mean eating under 1,000 kcal, which is hard to sustain and risks muscle loss, so the calculator shows a warning.
| Time frame | Weekly rate | Daily deficit |
|---|---|---|
| 10 weeks | 1.00 kg | 1,100 kcal |
| 20 weeks | 0.50 kg | 550 kcal |
| 30 weeks | 0.33 kg | 367 kcal |
| 40 weeks | 0.25 kg | 275 kcal |
A deficit of roughly 300 to 600 kcal a day, giving about 0.25 to 0.5 kg a week, is a pace most people can keep up while still eating normal meals. A rate up to 1 kg a week is generally considered the upper safe limit for adults without medical supervision.
The 7,700 kcal rule is a useful planning tool, but the scale will not follow a straight line. In the first week or two, weight often drops faster because the body releases stored carbohydrate and the water held with it. Later, progress slows: a lighter body burns fewer calories, so the same intake produces a smaller deficit. Daily weight can also swing by 1 kg or more with salt, water and digestion.
Weigh yourself at the same time of day, under the same conditions, and look at the weekly average. If the average has not moved for three or four weeks, recheck your calorie needs with a BMR calculator and trim intake or add activity slightly.
Indians tend to carry more body fat, especially around the waist, at a given BMI than Western populations, and develop diabetes and heart disease at lower weights. For this reason Indian consensus guidelines use lower BMI cut-offs: 18.5 to 22.9 is considered normal, 23 to 24.9 overweight and 25 or above obese. A waist measurement of 90 cm or more in men, or 80 cm or more in women, is another sign that losing weight would help.
Even a loss of 5 to 10% of body weight can improve blood sugar, blood pressure and cholesterol, so a first goal does not have to be your final one. If you have diabetes, heart disease or kidney problems, take regular medication, are pregnant, or plan to eat very little, talk to a doctor before starting. This calculator gives general estimates and is not medical advice.