How much more should I eat if I am pregnant?

300 calories. In general, 300 additional daily calories are all that is needed to ensure adequate fetal growth and optimal nutrition for mother and baby. Women who enter pregnancy significantly underweight may need to eat additional calories to compensate for their pre-pregnancy health status.
Not much more. If a woman is of normal weight before conceiving, she should really stick to a normal, healthy diet. The few hundred extra calories she may need will sneak into her diet without too much effort. The old adage of 'eating for two'; rather than be a license to eat whatever/whenever, should be a reminder that whatever you are eating, you are feeding your baby.
Eat normally. Sometimes in early pregnancy, you'll feel sick rather than hungry. If that happens, try eating at the first sign of nausea, a complex carbohydrate is best. If you eat the way the books say, you'll gain 70#. Eat what's good for you, and to your appetite. If you don't gain enough weight, your doctor will let you know.
Not Much. Pregnancy does add additional nutritional requirements, but you definitely are not eating for two. A normal well balanced diet supplemented with a prenatal vitamin should fulfill your nutritional requirements. The additional energy requirements associated with pregnancy amount to about 300 additional calories in a day, which is not much.
Depends. It depends entirely on what your starting weight is, whether or not you are overweight, whether or not you have diabetes, whether or not you have twins. If you are at ideal body weight beginning in your pregnancy then you will need about 300 cal/day. Just to put things into perspective, this is about half of one peanut butter an jelly sandwich. If you are overweight, then your goal is different.
340-452 Calories/day. It is recommended to eat an additional 340 calories/day in the second trimester and 452 calories/day in the third trimester.