How many calories do you need a day?

A moderately active female, 31 to 50, with a body mass index of 21.5 requires 2,000 calories per day to maintain her weight, according to WebMD. To lose weight at the suggested rate of 1 pound per week, she must reduce her caloric intake by 500 calories a day.

Many factors affect the daily requirement for calories, notes WebMD. Men generally require more calories than women. Highly active individuals burn more calories than sedentary individuals. The calorie requirements decrease as the person ages. Designing a maintainable weight loss plan includes foods to reduce calories while maintaining protein, nutrients and vitamins.