I’m using Lose-it now. When you start setting up your plan/goals it should ask you age, weight, normal activity level and then calculate your BMR + activity factor calories (that you’d burn on a normal day), and it will ask you how much you want to lose (total or per week) and when you want to lose it by and use that info to calculate how much deficit you need per day to lose that much weight, and it will subtract those deficit calories from the BMR+activity calories to give you your daily “budget” of calories you can eat.
Pretty sure you can manually adjust any of those numbers if you decide they need to be tweaked after a couple weeks, or whatever.