A web app to calculate the amount of calories you need to eat in a day to lose weight depends on your Total Daily Calorie Needs.
Use this Calorie Deficit Calculator, you can figure out your Basal Metabolic Rate, your Total Daily Calorie Needs and how many calories you should be eating to create a calorie deficit. The calculator will give you a few choices for a calorie deficit. If you’re not sure which calorie deficit to choose, go for the 20% calorie deficit. It’s moderate enough to show results, but not so aggressive you’ll be gnawing on wood out of hunger. Bear in mind, the results are estimates but it should give you a good starting point.