How many carbohydrates can a person have per day?

Here are two options. It depends on whether or not you want to lose weight. Therefore, this question is answered in two ways. 

THOSE WHO ARE NOT TRYING TO LOSE WEIGHT

If you are NOT trying to lose weight, 130 - 230 grams are sometimes recommended. However, please note that unlike protein and fats there is no minimum daily requirement of carbohydrate for good health or to sustain life. 

Someone consuming 2000 calories a day might be eating even 300 grams of carbohydrates (which is a lot). If you are asking the question in relation to weight loss and low carbohydrate diets, however, the recommended intake of carbs per day is far less. 

THOSE WHO ARE TRYING TO LOSE WEIGHT

If you ARE trying to lose weight, 20-60 grams are recommended. For weight loss, get your carbohydrates from natural sources such as (preferably organic) fresh non-starchy vegetables and low-carb fruits such as berries and avoid or cut right down on refined processed carbohydrates. 

FOR BOTH GROUPS FOR GOOD HEALTH:

Refined processed carbohydrates are a major cause of heart disease, hypertension, weight gain, obesity, and many other diet related diseases. Therefore, strictly limit (apart from the occasional treat) refined processed carbohydrates. Replace those foods with 'fat burning' foods and take advantage of the thermic effect of those foods to lose more body fat. If you are unsure what these foods are, you will find a list of refined carbohydrates and a list of fat burning foods, and for about the thermic effect of foods, further down this page under Sources and Related Links.