There is currently no true consensus among historians, authors, and educators for the precise dates - or even the general dates -- that mark the beginning and end of the medieval era. The most common time frame is approximately 500-1500 C.E., but you will often see different dates of significance marking the era's parameters.
The reasons for this imprecision become a little more clear when one considers that the Middle Ages as a period of study has evolved over centuries of scholarship.
Once a "Dark Age," then a romantic era and an "Age of Faith," medieval times were approached by historians in the 20th century as a complex, multifaceted era, and many scholars found new and intriguing topics to pursue. Every view of the Middle Ages had its own defining characteristics, which in turn had its own turning points and associated dates.
This state of affairs offers the scholar or enthusiast the opportunity to define the Middle Ages in the manner that best suits his own personal approach to the era. Unfortunately, it also leaves the newcomer to medieval studies with a certain amount of confusion.