There’s a simple formula to weight loss:
Calories In — Calories Burned = Weight Loss
But you probably have seen that. Now let’s actually break it down.
Calories In — This is pretty simple. It’s just the calories you intake in a day from whatever you ate or drank. Calorie counters like MyFitnessPal can help you track this easily.
Calories Burned — This is also pretty simple, although a bit harder to measure. If you exercised today, you burned some calories, which an app like Strava or Fitocracy can somewhat help you measure.
Weight Loss — This is the most complicated part of the equation, which is explained below. But if the left side of the equation is lower than your maintenance calorie count (i.e. the amount of calories you need to maintain your current weight), then you will lose weight.
If you think about this formula though, a couple of things become painfully apparent. First, even if you exercise for two hours a day, it is really hard to burn more than 1000 calories at the gym. On top of that, not everyone has two hours to spare a day to go the gym. This brings us to our second point: controlling the Calories In part of the formula is the easiest way to lose weight. Knowing that skipping out on desert with lunch is the equivalent of running or walking four miles (seriously!) might make you reconsider ordering that cookie or piece of cheesecake. Cutting out sodas and replacing them with tea or water is another surefire way to quickly cut out calories. And if you are craving caffeine, consider switching to regular coffee with skim milk instead of ordering the high-calorie frappucino. The difference between the a coffee with skim milk and a venti frappucino from Starbucks is over 500 calories… or an hour spent at the gym.
More detail on the Weight Loss part of the formula
Every person has their own basal metabolic rate (BMR), which is a fancy way of saying how many calories do you burn on a daily basis if you are at complete rest (i.e. lying down). To calculate how many calories you need to aim to burn/ingest in order to lose a certain amount of weight in 28 days, you should first start by calculating your BMR. Here is a pretty simple BMR calculator: http://www.bmi-calculator.net/bmr-calculator/. Once you have your BMR calculated, you will use the Harris-Benedict Formula to estimate your daily maintenance calorie levels:
Harris Benedict Formula
To determine your total daily calorie needs, multiply your BMR by the appropriate activity factor, as follows:
If you are sedentary (little or no exercise) : Calorie-Calculation = BMR x 1.2
If you are lightly active (light exercise/sports 1–3 days/week) : Calorie-Calculation = BMR x 1.375
If you are moderatetely active (moderate exercise/sports 3–5 days/week) : Calorie-Calculation = BMR x 1.55
If you are very active (hard exercise/sports 6–7 days a week) : Calorie-Calculation = BMR x 1.725
If you are extra active (very hard exercise/sports & physical job or 2x training) : Calorie-Calculation = BMR x 1.9
Once you have calculated your daily maintenance calorie levels, you can work backwards to solve for how many calories you should eat or burn. Here’s an example:
A 30 year old man weighs 250 lbs and is 6 feet tall. His BMR (per the calculator) is 2333.9. This man currently does not do much exercise, so we multiply his BMR by 1.2 per the Harris-Benedict Formula (2800.7). So if this man is aiming to lose 1 lb of weight per week, he would need to operate ~500 calories below his maintenance calorie requirement (2800.7). Specifically, if he managed to have a net caloric intake of 2300 calories per day (whether he ate 2300 and burned 0 or if he ate 2700 and burned 400 at the gym), he would lose 1 lb per week. There are ~3500 calories in 1 lb, so operating 500 below maintenance per day would burn 3500 calories in one week.