The appropriate abbreviations for month names in American English typically include the first three letters of the name. The abbreviated form of January, for example, is "Jan." September is a partial exception to the rule, as its correct abbreviation consists of the first four letters of the name, as in "Sept." Months whose names are fewer than five letters long are not typically abbreviated.
Nine out of the 12 months have names over five letters long, and of these nine, September is the only exception to the three-letter abbreviation rule. Some of the top universities in the United States, including Yale, Cornell and Princeton University, list the appropriate abbreviations for the remaining eight months as follows: January as "Jan," February as "Feb," March as "Mar," April as "Apr" and August as "Aug." In addition, October is abbreviated as "Oct," November as "Nov" and December as "Dec."
The remaining three months are May, June and July, all of which are fewer than five letters long. These names typically have no abbreviation and should be written in their complete form. The 16th edition of the Chicago Manual of Style, however, allows for a three-letter abbreviation of June and July, as in "Jun" and "Jul."