BMR (Basal Metabolic Rate) is an estimation of the amount of energy your body
burns if you stayed in bed all day. Unfortantely your BMR also decreases with age and loss of lean body mass.
To calculate the number of calories a person needs to maintain their weight, the BMR is multiplied by a number
of 1.2 to 1.9 corresponding to a person's activity level as follows:

1.2 - Sedentary

1.375 - Light activity (exercise 1-3 days/week)

1.55 - Moderate activity (exercise 3-5 days/week)

1.75 - High activity (exercise 6-7 days/week)

1.9 - Extreme activity (exercise 2x per day)

For more information on BMR, please see What is BMR. Please use the BMR calculator above to see what your estimates are for calories burned.
BMR Formula - BMR can be calculated using the Mifflin formula
For Imperial(US) measurements:
BMR = (4.5 * mass(lb)) + (15.9 * height (in)) - (5 * age) + s
For metric:
BMR = (10 * mass(kg)) + (6.25 * height (cm)) - (5 * age) + s
*where s is +5 for males and -161 for females.
Please consult a medical professional if you have any questions regarding your BMR.