how to lose weight - a very basic scientific guide

※ TDEE: total daily energy expenditure

※ BMR: Basal metabolic rate

1) calculate your BMR

BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161

or use a website:
https://www.calculator.net/bmr-calculator.html

2) calculate your TDEE

sedentary TDEE = BMR x 1.2

lightly active TDEE = BMR x 1.375

very active TDEE = BMR x 1.725

extremely active TDEE = BMR x 1.9

or use a website:
https://www.calculator.net/tdee-calculator.html

3) eat according to your TDEE

if you eat the same calories as your TDEE, you will MAINTAIN

if you eat over your TDEE, you will GAIN

if you eat below your TDEE, you will LOSE

1 lb of fat ≈ 3500 calories, therefore:

if you eat 500 calories less than your TDEE, you will lose 1lb a week

if you eat 2000 calories less than your TDEE you will lose 4lb a week

You may compensate overeating with exercise.

If you eat 500cals over your TDEE but burn 500cals, you will MAINTAIN.

If you eat at your TDEE but burn 500 cals you will LOSE 1lb a week.

if you eat 500cals below your TDEE and burn 500 cals you will LOSE 2lb a week.

if you eat 2000cals below your TDEE and burn 500cals you will LOSE 5lb a week.

TL;DR: Calories in < Calories out. (CICO).
http://justcico.com 
※ Results may differ if you suffer from hormonal imbalances or are taking certain meds.

i made this thread because there seems to be a lot of misinformation, and some folks who are afraid they'll gain while eating less than their TDEE (i.e. "i ate 800 calories today will i gain fat?"). Hopefully this informs them of how weight gain/loss works.

you cannot gain any fat while eating at maintenance or deficit. if the scale goes up, it's water retention.