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Stands forJan., Feb., Mar., Apr., Aug., Sept., Oct., Nov., Dec.; mo. for month

abbreviationSaid as the full month name

Month Abbreviation Guide: Every Month, Shortened

WordsDatesCalendarsUpdated Oct 30

The standard month abbreviation in American writing is the first three or four letters with a period: Jan., Feb., Mar., Apr., Aug., Sept., Oct., Nov. and Dec. May, June and July are short already, so most writers leave them whole. If you need the abbreviation for the word "month" itself, it is mo., and the plural is mos.

The right choice shifts with the setting. A calendar header, a school form, a news story and a spreadsheet each have their own habits, and the chart below shows them side by side.

Quick facts

  • Standard style

    Jan., Feb., Mar., Apr., Aug., Sept., Oct., Nov., Dec.

  • Left whole

    May, June, July (often March and April too)

  • Three letter codes

    JAN, FEB, MAR and so on, often without periods

  • Word "month"

    mo., plural mos.

  • Period

    Yes in running text; usually dropped in tables and codes

  • Capital letter

    Always, since month names are proper nouns

  • September

    Sept. in most US styles; Sep. in three letter systems

Month abbreviation chart

All twelve months in three common styles
MonthStandard abbreviationThree letter codeNews style with a date
JanuaryJan.JANJan.
FebruaryFeb.FEBFeb.
MarchMar.MARMarch
AprilApr.APRApril
MayMayMAYMay
JuneJune (or Jun.)JUNJune
JulyJuly (or Jul.)JULJuly
AugustAug.AUGAug.
SeptemberSept. (or Sep.)SEPSept.
OctoberOct.OCTOct.
NovemberNov.NOVNov.
DecemberDec.DECDec.

The middle columns cover most needs. Use the standard column in letters, notes and forms. Use the three letter column for tight spaces such as calendar grids, receipts and data files. The last column follows a common newspaper rule, explained below.

When to abbreviate a month and when to spell it out

Many American style guides, especially news style, follow one simple rule: shorten a month only when it comes right before a day number.

  • Shorten: "The fair opens Aug. 14."
  • Spell out with a month alone: "The fair opens in August."
  • Spell out with a month and year only: "The bridge opened in August 1957."
  • Never shorten March, April, May, June or July in that style, even with a date.

Formal letters, invitations and school essays usually spell every month out. Save the short forms for places where space is limited or the tone is relaxed, such as notes, charts and footnotes.

Abbreviations of months on forms and calendars

Printed calendars and date pickers often use three letters with no period: JAN, FEB, MAR. Some go even shorter, with one letter per month (J F M A M J J A S O N D), which only works in a grid where the order makes the meaning clear.

On a medical form: "Date of birth: 07 / MAR / 1990." Writing the month as letters avoids the mix up between 07/03 meaning July 3 in the US and March 7 in many other countries.

For records and computer files, an all number date such as 1990-03-07 sorts cleanly and avoids words altogether.

The abbreviation for month itself

When the word "month" appears in a unit, write mo. for one and mos. for more than one. You will see it in loans, leases, warranties and ages.

  • "Lease: 12 mos."
  • "Baby boy, 9 mo."
  • "Warranty: 6 mo. parts and labor."
  • "Billed per mo." on a phone plan chart

Do not confuse it with MO in capitals, which is the postal code for Missouri and also short for modus operandi. The page on MO sorts those out.

Periods, capitals and plurals

  • Period: add one after a shortened month in sentences: Oct. 9. Leave it off in three letter codes: OCT 9.
  • Capitals: month names and their short forms always start with a capital letter: Nov., never nov.
  • No period on full words: May, June and July have nothing removed, so they take no period.
  • Plurals: rare, but write "the Januarys" for the full word; avoid pluralizing the short forms.
  • Day names: follow the same pattern, such as Thurs. or Thu. See the Thursday abbreviation page.

Months people get wrong

Three months cause most of the mistakes.

  • September: Sept. is the usual American style. Sep. appears in three letter systems where every month needs the same length. See the September abbreviation page.
  • March: Mar. is correct in a chart, but news style spells it out. More on the March abbreviation page.
  • June and July: Jun. and Jul. exist in codes, but Jun. can be misread at a glance, so most people write the full word.

For other everyday short forms, the common abbreviations section has days, units, titles and address words.

Questions people ask

What is the abbreviation for month?

The abbreviation for month is mo., with a period. The plural, months, is mos. You will see it on leases, loan terms and baby ages.

What are the 3 letter month abbreviations?

They are JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV and DEC. They are common on calendars, receipts and data files, often in capitals with no period.

Do months abbreviation forms need a period?

In sentences, yes: Jan. 5, Dec. 31. In three letter codes and tight tables, the period is usually left off.

Is it Sept. or Sep.?

Both are used. Sept. is the more common American choice in writing, while Sep. fits systems where every month uses exactly three letters.

Why is May never abbreviated?

May has only three letters, so there is nothing to shorten. Writing "May." with a period would be wrong, since no letters were removed.