Question: how to calculate how much i should be eating?
Answer: Women: 10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) – 161 = REE. Men: 10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) + 5 = REE.
Choose an activity level: ... 
Eat more calories than presented to gain weight, eat less to lose weight, and eat the same amount to maintain your weight.