The Jewish year is not the same length as a solar year used by most of the western world. Months are either 29-30 days, corresponding to the 29½-day lunar cycle. Years are either 12 or 13 months, corresponding to the 12.4 month solar cycle. The Jewish calendar uses a 12-month lunar calendar with an extra month occasionally added. Jews do not generally use the words A.D. and B.C. Instead, C.E. (Common or Christian Era) and B.C.E. (Before the Common Era) are commonly used by scholars today.