Reply To: What percentage of conservative and reform are halachically jewish?

It is a function of how long they have been off the derekh. In the case of the “classic” Reform Jews from Germany who went off the derekh in the early to mid-19th century, probably an overwhelming percentage, especially if they have a Jewish surname. In the case of East European Jews who came in the 20th century, the percentage will be less. I think at this point one car probably assume that a self-proclaimed Reform or Conservative Jew is a safek goy (meaning they are also a safek Yid). Depending on whether one holds that non-Orthodox Jewish weddings are valid, most would be safek mamzerim as well (cf. situation with Ethiopian Jews were were safek goy, safer mamzer).