AD dates are traditionally formatted by writing “AD” before the year (e.g., AD 400) but can sometimes be found with “AD” placed after the year (e.g., 400 AD).
“AD” indicates years after the assumed birth of Jesus Christ, starting with AD 1, all the way until the present day.
However, in modern usage, “AD” is often omitted for dates after the first century, especially in informal contexts. For example, the use of “AD” is not necessary when referring to the year 2024.