I used some tool online to calculate it based on my weight, height, activity, etc, but yeah it was essentially that if I'm eating 2400 kcal per day I'll have constant weight, if I'm eating 2000 kcal and less I'm losing weight. Then it's 1kg weight loss = 8000 kcal deficit. I used MyFitnessPal to track it and you can modify the target calorie number in MFP based on what you are trying to achieve.

Overall I think when you are fat, then start strength exercise to get muscles under the fat (for like 6 months) and after that you can do some weight loss.

If you first start losing weight and get skinny, then the next step you feel like you actually want some muscles, so you will need to eat a lot again anyway.