RadicalBehavior.com has a handy formula to calculate the number of calories one should eat in a day.

To do a simplistic calorie content for me each day, I use the light activity setting and then add all the activities I do to get the count of all the calories I should be doing. For instance, if I run for 30 minutes, I add the calories I should I burn doing that activity to the calories calculated from that formula to decide how many calories total I should eat. It’s not exact, but it works for me.

I added a simple Daily Calorie Calculator here using RadicalBehavior.com’s formula. You can find it here.