Medically reviewed by Suzanne Fisher, RD Key Takeaways Body mass index (BMI) is a calculation used to estimate your body fat.

You can calculate weight loss as a percentage of your total body weight. Here's how to calculate weight loss percentage and why it matters.

Whether you want to gain or lose weight, you need to know how many calories you burn in a day, or your TDEE (total daily energy expenditure). Here's how to figure it out.