Your body needs calories to do it's day-to-day stuff. How many depends on a few different factors, you can calculate it with a tool like this:

https://www.verywellfit.com/how-many-calories-do-i-burn-every-day-3495464

If you eat more calories than that, you will gain weight. If you eat fewer (calorie deficit) you will lose weight.

You can get an online calculator of how many calories your body uses up everyday, just Google search it. You then read the packs of food you buy or do a search of the food you eat on Google and there should be a calorie amount on them. You want to aim for a 250-500 calories deficit a day from what your body uses up to what to eat. 1lb of fat = a 3500 calorie deficit.

A calorie deficit is when the number of calories you take in is less than the calories you burn in a given period, generally a day.

If you eat 1800 calories, to achieve a deficit you must burn more than that. For instance, I heard a long time ago that a single jumping jack burns 1/2 a calorie.

There is a thing called resting metabolic rate, which tells you the number of calories burned just staying alive in a day. This will be helpful to know, you can consider it the "minimum burned calories" in the sense that everything you do in a day burns additional calories. (E.g. I'm 6'1", 200lb 27 year old male, mine is 1800-2100 depending on the rough calculation)

Everything you eat counts against calories burned. If you want to stay in a deficit, you need to balance calories with exercise. You do not need to do a 10,000 calorie exercise to justify a 500 calorie treat, but maybe monitor your other choices that day.

It is important to note that you can achieve calorie deficit without exercise, but also the effects of exercise are wonderful and it allows you to "live a little" with food choices while trying to maintain a caloric deficit.

Best of luck on your journey.

It's actually quite simple and it involves the food you eat and how much energy your body uses throughout the day. A calorie is a simple measurement of the stored energy within a given food that we can consume.

1 calorie in food is how much energy it takes to raise one kilogram of water one degree Celsius when burned in a controlled environment. It's an imperfect science because there are things like fiber that will burn in this setup but do not confer energy to a human body.

Your body needs a set amount of energy (calories) to operate throughout the day depending on your muscle mass, body size, gender/sex, and activity. This is your baseline calorie need for a given 24 hour period.

Now, you eat food throughout the day and that has a caloric value. If you eat less calories than your body uses then you have a calorie deficit for the day and assuming you have eaten healthy and your body's endocannabinoid system (pancreas, thyroid, etc.) is healthy then you will either consume fat stores or muscle mass to maintain necessary bodily functions. If there are insufficient fat or muscle stores in your body then you start to consume major organs until death occurs.

TL:DR eat less than you require and you're at a calorie deficit. To bolster weight loss, gain muscle mass as that is the most energy hungry thing you can control the amount of in your body.

Rent takes money from your bank account. Gas takes money from your bank account. Paychecks put money into your bank account.

If you spend more than you make, you are in a financial deficit and this will negatively impact your credit.

Running takes calories from your body account. Lifting weights takes calories from your body account. Eating food puts calories into your body account.

If you spend more calories than food you eat this will put you into a caloric deficit and that will negatively impact your weight.

A minor caloric deficit sustained over time will help you lose weight sustainably provided you have weight to lose in a healthy manner.

If you do not have weight to lose in a healthy manner then a caloric deficit will cause you to lose mass in a less than desirable way. You can technically be eating everyday and still die to starvation for example.

Eating less calories than your body burns is being in caloric deficit

In general, it takes 9-15 calories per pound to maintain your body weight, depending on how active you are. If you are mostly sedentary, it's around 9, if you are moderately active it's around 12, if you are very active it's around 15

So if you are moderately active person (12 calories per pound to maintain your weight) and you weigh 250 pounds, you daily caloric requirement is 250 * 12 = 3000 calories. If you eat 3000 calories a day, you are at caloric stasis, and you will stay 250, if you eat more that 3000 calories a day, you are in caloric excess, and will gain weight. If you eat less than 3000 calories a day, you are in caloric deficit, and you will lose weight

These are all generalities, every body and metabolism is unique and can modify these numbers a bit.

1. Find out how many calories you need for YOUR body in a day. Each person has a different calorie amount. Use an online calculator for it. Me for example I need 1300 kcal to function.

2. Find out how many times a day you like to eat. I eat three times a day, so I would give myself a calorie budget: “For breakfast I will only eat 400 kcal”. For each meal, give it a calorie budget and plan not eat foods that go over this budget.

E.g. breakfast: 400kcal allowed Lunch: 500 kcal allowed Dinner: 300 kcal allowed Snack: 100 kcal allowed

3. Find recipes for meals that fall into or under your allotted calorie count for each meal.

4. End of the day, add up your combined calorie spendage and make sure it is not over your total allotment for the day. So If I have eaten 1,290-1,330 kcal then I am doing good. Myfitnesspal is great for logging your calories. I recommend a good app and get into the habit of logging calories.

5. Be honest and be kind to yourself. If I go over by 200 kcal a day, I make sure to log it, however I try to add in a bit of walking/yoga to try and burn off the excess calories and get my total for the day back to 1300 again. I dont beat myself about it because some days you really do need some chocolate or a milkshake.

If this sounds like a ton of work and intimidating, it can be to begin with but after a week or three you'll start memorizing how many calories are in what, and begin to start being able to make decent estimates of unknown foods. Which for the most part is fine if you're not consistently guessing either low or high. I don't calorie count anymore, but it was rare that I actually needed to check a label unless it was a prepackaged food I hadn't eaten before.

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Almost everything you eat contains nutrients that your body can convert into energy. It uses this energy to power your organs, muscles, brains, pretty much everything you need to survive.

Because there are a lot of different nutrients, and a lot of different ways for your body to store or convert this energy, we use a standardized unit of measurement called a calorie. This unit can be used to define how much 'energy' a certain kind of food has, and how much 'energy' your body needs to perform a specific function. When the amount of energy you eat is less than the amount of energy your body uses, you are said to be in a 'calorie deficit'. Usually this measured over the period of a day, i.e. how much did you eat today vs. how much energy did you expend.

But what does this mean for your body? If you are consuming less calories than your body is using to keep you alive, where does the remaining energy come from? well, whenever you are in a calorie surplus (which is, as you might expect, the exact opposite of a deficit - we are consuming more energy than we are expending), your body stores the remaining, unused, energy as fat, to be used at a later time. Then, whenever we are in a deficit, these stored fat cells are converted back into usable energy.

From this, you can also see why eating more than our body needs causes us to gain weight: the surplus calories are stored as fat cells. And when we start consuming less food so that we are in a calorie deficit, we lose weight because the stored fat cells are used to generate the needed energy.

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