Most improve by 3-4 months, but for some it's not until 5 or 6 months or even later.
If it turns out to be GER instead of colic (they don't know for sure what causes colic, but there are many theories), then it will usually improve by 6 months or when they start solid foods, but they may continue to have some problems later on. My DS has a moderate case of GER, so he had colic like symptoms for his first 6 months. He still gained weight adequately, so it wasn't a severe problem. It improved significantly after 6 months, but he still has problems now and then (he's 2 now). I think it probably feels like heartburn does to an adult, and he gets inconsolably fussy when he has problems with it. We tried to keep our DS upright after eating and fed him smaller amounts more often than average each day, and that seemed to help him spit up less and gain weight adequately.
at 11:50 PM on Nov. 1, 2010