Great question actually, and far from a simple answer. Let me explain....
What you CAN do, is jump online to one of many calorie calculators, and once you've entered your age, gender, weight, and activity level you'll get a magic number!
Remember - this is based on several assumptions and is population based, so for the AVERAGE person who fits that data you entered, the calorie intake they suggest will be *about* right.
It's a good starting point and certainly if someone requires 2000 calories per day but routinely consumes 4000 calories, results will come quite easily once calorie intake is adjusted.
THERE IS though a lot to consider, because of course we are all different. In fact, the biological difference between humans astounds me, and I've been a student of how the body works for almost 3 decades...... we are all so so different, there is no such thing as "one size fits all" - this goes for training too, that's why coaches exist.
Consider this - person A consumes 2000 calories of mostly sugar and refined carbohydrates, versus person B who also consumes 2000 calories but has more healthy fats, more protein, no added sugar, and also has lots of low calorie vegetables. Same calorie intake, VASTLY different impact on blood sugar levels AND hormonal response to foods.
Keeping your blood sugar level stable, and therefore a smoother insulin response to food, is a good goal for starting out because that lets the body shift into fat burning states, and also tends to help our brains function much better.
What I've worked with for many years now is a combination of a persons nutrition, their training, AND their hormones or brain chemistry. All are very important. I've seen people with the perfect training plan and dietary intake NOT get results, because they were getting terrible sleep, taking on too many daily tasks, and living in a highly stressed state. This elevates stress hormones and the body vastly shift metabolic processes around to counter that.
PRO TIP>>> you can have equal calorie intake and calorie burn, and still lose or gain weight depending on what your metabolism is doing.
SO - here are some questions to ask yourself:
How are my general daily energy levels?
How are my energy levels while training?
Am I gaining, losing, or maintaining body fat levels?
These 3 questions form the backbone of how I'll start to decide whether someone's calorie intake is about right or not. I've found them to be the best 3 questions to look at.
If you are struggling with energy levels for example, you might be too low with your calorie intake, equally though you might be over-training or fatigued from poor quality sleep or poor quantity of sleep.
How is your weight and or body fat level? Going up? Down?
This is a very good indicator of where your calorie intake is right now.
SO - not a simple answer sorry, but certainly some things for you to think about.