AD is sometimes misinterpreted as being an abbreviation for "after death," referring specifically to the death of [[Jesus Christ]]. This causes the common confusion resulting from the general consensus is that Jesus died roughly AD 32.
In general, English usage follows Latin by placing the abbreviation ''before'' the year number for AD, but ''after'' the year number for BC, although there are several exceptions to the first part of this principle. Constructions such as "the fourth century AD" are widely accepted, but constructions using full month-and-day with '''AD''' do not work (one does not write "September 11, 2001, AD").
[[BC]] is an English [[initialism]] meaning "Before Christ" and always is the last element. If the context does not otherwise indicate we are in such times, one is obligated to use the form. One can use it with full explicit dates, e.g., "Julius Caesar was killed March 15, 44 BC".