Calorie Deficit Calculator

How this is calculated

1. Maintenance calories. The starting point is your Estimated Energy Requirement from the 2023 National Academies equations, the same as on the maintenance calorie calculator. The report says plainly that these equations are not designed for weight loss; they estimate what keeps your weight steady. That makes them a starting point to subtract from, not a promise.

2. The deficit. The 2013 guideline for adults with overweight or obesity from the American Heart Association, American College of Cardiology and The Obesity Society, started by the NIH’s National Heart, Lung, and Blood Institute, lists three ways to cut calories: a deficit of 500 or 750 calories a day; 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men; or an evidence-based diet that leaves out certain foods. It says diets under 800 calories a day should be used only in a medical setting with medical supervision.

Example: a 45-year-old inactive woman, 5 feet 4 inches and 190 pounds, has an estimated maintenance of 2,208 calories. With 500 a day less she eats 1,708; with 750 less, 1,458.

3. How fast. The common rule says a pound of body weight is 3,500 calories, so 500 a day less would be a pound a week, 52 pounds a year, forever. It is wrong because your body burns less as it gets smaller. Kevin Hall and colleagues at the NIH built a model of this and give a rule of thumb for an average adult with overweight: every 10 calories a day less leads to about 1 pound less in the end, with about half of that reached in about a year and 95% in about three years. In their example, the 3,500-calorie rule predicts about twice the first-year loss of the model.

Even over one to three months the old rule overshoots: in seven tightly controlled studies, people lost 20.1 pounds on average where the 3,500-calorie rule predicted 27.6 (Thomas and colleagues, 2013). Hall’s team also found that people with more body fat lose more in the end but take longer to get there. For a curve that fits your own numbers, the NIH Body Weight Planner runs the full model.

4. The uncertainty. Your real maintenance can be several hundred calories above or below the estimate. The National Academies show how to handle that: below your estimate minus 1.96 standard errors, almost everyone with your numbers loses weight. The result shows that number. The CDC adds that people who lose weight at a gradual, steady pace of about 1 to 2 pounds a week are more likely to keep it off.

Who should talk to a doctor first

Anyone under 19, pregnant or breastfeeding, with a BMI under 25, or with an eating disorder now or in the past should ask a doctor before cutting calories. The guideline’s calorie targets are meant for adults with overweight or obesity. The calculator warns when your BMI is in the healthy or underweight range, when the target falls below the guideline’s ranges or under 800 calories, and when the deficit would, by the rule of thumb, take your BMI under 18.5.