The usual September abbreviation in American writing is Sept., with four letters and a period. Calendars, spreadsheets, apps and forms that give every month three letters use Sep or Sep. instead. Both are correct; they just belong to different places.
September is also one of the few months that people often shorten with four letters rather than three. That makes it a common question on school forms and in work emails, where writers want the month to look tidy next to Jan., Feb. and Oct.
Quick facts
News and general writing
Sept.Three letter style
Sep or Sep.All caps on forms
SEPAs a number
9 or 09Period
Yes for Sept.; optional for SepPlural
Rarely needed; write Septembers in full
Which September abbreviation should you use?
| Form | Where it is used | Example |
|---|---|---|
| Sept. | News stories, letters, school papers, most American style guides | Sept. 14 |
| Sep. | Some reference books and style guides that shorten every month to three letters | Sep. 14 |
| Sep | Calendar apps, spreadsheets, data tables, date pickers | 14 Sep |
| SEP | Military dates, shipping labels, credit card style forms | 14 SEP |
| 9 or 09 | Numeric dates on forms and records | 9/14 or 09/14 |
If you are writing for a general American reader, pick Sept. It is what most readers expect. If your document already uses three letters for every month, match that pattern with Sep.
The news writing rule
American news style shortens a month only when it sits next to a specific date. The months that get shortened are Jan., Feb., Aug., Sept., Oct., Nov. and Dec. March, April, May, June and July are always written in full.
- Shortened: "The meeting is on Sept. 8."
- Full, no date: "The meeting is in September."
- Full, month and year only: "The school opened in September 1965."
This is why you will see Sept. in a news story but the full word in a heading such as "September events." The same rule covers August and keeps June and March spelled out.
Writing September on forms, calendars and data
Forms rarely leave room for long words. A three letter box, a date picker or a spreadsheet column usually shows SEP or Sep.
On a medical intake form: "Date of birth: DD MMM YYYY." You would write something like "21 SEP" followed by the year. The three letter code keeps the month from being misread, which can happen with numbers alone.
In numeric dates, September is month 9. American order puts the month first (9/21), while many other countries put the day first (21/9). If an international reader will see the date, writing the month as Sep avoids that confusion.
Periods, capitals and spacing
- Capital S: month names and their short forms are always capitalized in English.
- Period after Sept.: yes in American running text. If the sentence ends with it, one period does both jobs.
- Period after Sep: optional. Data and calendar styles drop it; some printed guides keep it.
- No apostrophe: never write Sep' or Sept'.
- Comma with year: "Sept. 9, 1957, was a Monday" puts a comma after the year in mid sentence.
For the full set of month short forms in one place, see the abbreviation for months guide.
Why September is the ninth month
The name comes from the Latin word septem, meaning seven. In the earliest Roman calendar, the year started in March, so September really was the seventh month. When January and February were later placed at the start of the year, the names stayed and September became the ninth month.
October, November and December followed the same path, from the Latin words for eight, nine and ten. September has 30 days, and in the United States it holds Labor Day, the first Monday of the month.
Examples in everyday writing
- Invitation: "Join us Saturday, Sept. 20, at 4 p.m."
- Spreadsheet column: "Sep" next to Aug and Oct.
- Work email: "The report is due Sept. 30."
- Shipping label: "Ship date 05 SEP."
- School calendar: "No classes in early September for the holiday."
More short forms used on dates, addresses and forms sit together in the common abbreviations section.
Questions people ask
How do you abbreviate September?
In American writing it is usually Sept. Calendars, apps and forms often use the three letter Sep, and some forms use SEP in capitals.
Is it Sep or Sept?
Both are correct. Sept. is the common choice in sentences and news writing, while Sep fits systems that give every month exactly three letters.
Does the September abbreviation need a period?
Sept. takes a period in American style. Sep can go either way; data and calendar layouts usually leave the period off.
What number month is September?
September is the ninth month, so it is written 9 or 09 in numeric dates.
Why does September mean seven?
The name comes from the Latin word for seven. It was the seventh month in the early Roman calendar, before January and February were moved to the front of the year.