Your body is constantly burning calories keeping you alive. It takes energy to keep your heart beating and your lungs breathing. Digesting food, driving to work, sleeping; you are burning calories. This is called your basal metabolic rate (BMR). You may call them slacker calories if you would like.
This is the MINIMUM calories necessary for life. Going below these will not benefit you or your weight loss goals in the long run. Going below this will simply drop your metabolism into starvation mode. Starvation mode screws up hormone production, energy levels, mood, and general homeostasis. Your body is in crisis mode so it holds on to everything it can to keep you alive. Humans are wired to survive.
With that being said, begin to think of food as fuel instead of the enemy. All of your energy comes from food! Feed your body well! I'm convinced you cannot have science without math... So, get out a calculator, pen and paper- here's the equations!
Hate math more than me? There's an app and online calculators that will do it for you. Ok, so we have your BMR. You now know how many minimum calories to eat each day to sustain life. But you want to lose weight, so we must do more math. See the equations "target daily calorie needs"? You will now multiply your BMR by one of those numbers, which are associated with your activity level. Be brutally honest, lying about it hurts no one but yourself! Here you get to create wiggle room! If some days are killer two-a-days and others are rest days, you can either create different calorie goals based on the day or you can take an average.
This new number is how many calories you need each day to maintain your current weight. Ready for more numbers? There are 3,500 calories in 1 pound! Want to lose 1 pound a week? 3,500 cal/ 7 days= 500 cal/ day deficit. You may reach this deficit by nutrition or exercise, or a mix. I like to create a 500 calorie deficit in my meal plans and then 1-2 days a week really ramp up my exercise intensity to burn a few extra hundred calories for good measure. Find what works for you, is realistic, and sustainable.
These days there are various tools to help you. My fitness pal is a favorite food logging app of mine, and my polar heart rate monitor and fit but charge help too. Weight loss will always require a calorie deficit of some kind; whether it is from food or exercise. Now, you have probably heard of IIFYM/ macro meal plans. Eat whatever you want within your macros and still lose weight! Well these macro calculators take into account your BMR and your goals, so you are still going into a deficit. I have a blog on IIFYM if you are more interested in learning how to calculate specific carbohydrate, protein, and fat needs.
I hope this has helped. As a certified personal trainer and a certified fitness nutrition specialist, I have a passion to help people. Please don't hesitate to email me at firstname.lastname@example.org with any questions!
My calculated BMR: from an app!
I personally usually shoot for 1,560-1,620 calories per day, with 35% carbs, 35% protein, and 30% fat. Keep in mind, every person is different so what works for me may not work for you. It takes patience and practice! One thing I will tell you though is that I always try to make healthy food choices, I never feel guilty about my food choices, and even after days where I ate over my calorie allotment, I still wake up looking good. If you are physically hungry; eat! Starving yourself does no good.