Ultimately, losing weight is all about calories in, calories out. In order to lose weight, you have to burn more calories than you take in. "You have to create a deficit of 3,500 calories to lose one pound," explained registered dietitian and ACSM-certified personal trainer Jim White, owner of Jim White Fitness and Nutrition Studios. "This can be done by burning extra calories through exercise or reducing your intake of calories, but the best way is to use a combination of both methods. This ensures that you're giving your body enough nutrients during periods of weight loss."
However, eating in a 3,500-calorie deficit doesn't guarantee an exact weight loss of one pound. There are a lot of other factors that impact how your body loses weight, including stress, sleep, and hormones.
Although you should eat in a calorie deficit, he doesn't recommend anyone eat fewer than 1,200 calories a day. And since calorie needs are highly individual from person to person, Jim recommends meeting with a registered dietitian if you can to assess your needs and your goals. If that's not a possibility, you can use this formula to calculate your estimated calorie deficit for weight loss.