Basic Metabolic Rate (BMR) is the minimum calorific requirement or number of calories your body will burn when you are resting or sleeping in bed.
Harris Benedict Equation given below can be used to calculate BMR and based on it your calorie requirement:
BMR for men =
66 + (13.7 x weight in kg) +
(5 x height in cm) - (6.8 x age in years)
BMR for women =
65 + (9.6 x weight in kg) +
(1.8 x height in cm) - (4.7 x age in years)
To increase your BMR, you need to exercise which would then improve your health and fitness.
More about BMR in posts to follow. Till then keep try increasing your BMR.