If you know you basal metabolic rate (estimating calculators available online if you don’t know your exact muscle mass) you can estimate how many calories you burn per day when factoring in your additional daily activity.
1 kg is 7,700 calories.
I typically burn close to a pound a day during an extended fast (after initial water weight loss).
if you are mildly overweight / mildly fat, you would burn about 0.22 kg (1/2 lb) each day you dont eat. a 72 hr fast yields about -0.45 kg (-1 lb) depending on how much you eat during fast break of day 3.
to know more accurately, find out your daily maintenance calories. whatever those maintenance calories are will the the amount of stored fat calories you lose each entire day you skip eating.