How to Calculate Your Maintenance Calories for Weight Loss

I am just starting my fitness journey and I am a bit confused about how many calories I should actually be eating. I have used several online calculators to find my Total Daily Energy Expenditure but each one gives me a different number. One says 2800 calories while another says 2400.

I live in California and work a fairly sedentary job as a graphic designer so I do not move much during the day. I have started going to the gym three times a week for light weightlifting. I want to lose about fifteen pounds before summer but I do not want to starve myself or lose muscle mass in the process.

Does anyone have a reliable method or a specific app they recommend for tracking? I have heard that MyFitnessPal is good but I am curious if there are better ways to adjust the numbers based on real world results. Should I just pick the average of all the calculators and see what happens after two weeks?

I am also wondering how much I should subtract from that maintenance figure to stay in a healthy deficit. I do not want to go too low and ruin my metabolism. Any advice from people who have successfully navigated this would be amazing.