Not sure if you tried this calculator but just posting anyway ... You can also try this calorie calculator
. Just enter your age, height, weight, target weight, activity level, the amount of calories you burn with exercise and when you want to reach your goal then it will show you the calories you need to reach your target.
You can also use the weight predictor
to see what weight you will be based on how much calories you're consuming and burning now. Helps to figure out how much you need and should burn to reach target on time, pretty useful for those on challenges here. In the end though, these calculators are just estimates so you can just follow these result, see if it works and adjust your calorie intake accordingly.