BMR - Basal metabolic rate is the minimal rate of energy expenditure per unit time by endothermic animals at rest. It is calculated in energy units per unit time e.g. Calories/day.
In a layman term it defines how much energy or calories needed per day. A strict set of criteria met to measurement of BMR including physical & psychological non disturbed state in a neutral environment. If temperature data is removed from BMR it become standard metabolic rate (SMR).
After the age of 20 BMR declines by 1 to % in 10 years.
There are various formula to to calculate the BMR but calc.co.in uses the most commonly used i.e. Mifflin - St Jeor equation.
BMR formula is different for man & female. Below is listed formula for man & female.

**For Man :** bmr = 10*w+ 6.25*h - 5*y + 5

**For Woman :** bmr = 10 * w + 6.25 * h - 5 * y - 161

where

w is weight in KG

h is height in centimetre(CM)

y is age in year.