To estimate the number of calories that you should eat, you also need to know your level of activity. If you are very active, you will need more calories than if you are sedentary. While it is relatively easy to estimate the number of calories in your food by weighing and measuring, it is a lot harder to estimate the number of calories burned by exercise. People often overestimate their amount of activity and consequently they eat more calories than they burn, and gain weight over time.

The Calorie Restriction Calculator estimates the Basal Metabolic Rate, and then uses an activity factor to obtain the total number of calories needed per day. Using the wrong activity factor alters the estimate of daily calories substantially.

A paper on metabolism used a definition of “vigorous exercise” as expenditure of 14.1 to 16.3 kcal/kg of ideal body weight per day.[1] Using the rounded figure of 15 Calories per kilogram of body weight, then “vigorous exercise” for a person weighing 150 pounds (68 kilograms) corresponds to 1020 Calories per day. If walking at 4 miles per hour burns about 300 Calories per hour, then you would need to walk 3 hours and 24 minutes to burn off 1020 Calories.

The activity factors for the Calorie Restriction Calculator are:

- 1.200 = sedentary (little or no exercise)
- 1.375 = lightly active (light exercise/sports 1-3 days/week, approx. 590 Cal/day)
- 1.550 = moderately active (moderate exercise/sports 3-5 days/week, approx. 870 Cal/day)
- 1.725 = very active (hard exercise/sports 6-7 days a week, approx. 1150 Cal/day)
- 1.900 = extra active (very hard exercise/sports and physical job, approx. 1580 Cal/day)

The activity factor **lightly active** corresponds to walking 2 hours per day, **moderately active** corresponds to walking 3 hours per day, **very active** corresponds to walking 4 hours per day, and **extra active** corresponds to walking 5 hours per day (20 miles). More strenuous exercises, such as climbing stairs or running, burn more calories per hour. Most people who exercise from 30 minutes to 45 minutes per day are in the “lightly active” category. You can use the CR calculator to determine the number of calories for each level of exercise for your particular weight by subtracting the calories for a specific activity level from the calories for the sedentary option.

**See the chart listing the calories for various activities**

[1] Thissen JP, Ketelslegers JM, Underwood LE., Nutritional regulation of the insulin-like growth factors, Endocr Rev. 1994 Feb;15(1):80-101. Review. PMID: 8156941