Module 12, Punctuation: End Marks and Commas, Lesson 2:

Periods in Abbreviations


Definition: An abbreviation is a shortened form of a word. There are different kinds of abbreviations. Some use periods; others don't. Some are written in capital letters; others use lowercase letters. This is an area that is changing rapidly. It is always best to check a dictionary or a style manual to be certain.

People's Names and Titles

Abbreviations in people's names and titles generally do use periods, but academic degrees and Roman numerals do not require periods.

People's Names People's Titles
John Q. Adams (Quincy)
S. E. Hinton (Susan Eloise Hinton)
(Also notice that there is a space after the first initial in the second example.)
Mr. (Mister)
Mrs. (Missus, short for Mistress)
Dr. (Doctor)
Jr. (Junior)
Sr. (Senior)
No Periods
Roman Numerals
(after names of people or events)
Academic Degrees
John Parker III (pronounced John Parker the third, not John Parker three)
World War II
BA (Bachelor of Arts)
MA (Master of Arts)
PhD (Doctor of Philosophy)
RN (Registered Nurse)

Days and Months, Latin Phrases, Addresses Directions, and Traditional State vs. Postal State Abbreviations

Months Days of the Week: Abbreviations of Three Letters or More Addresses Latin Phrases Traditional State Abbreviations
(not frequently used anymore)
Jan. (January) Mon. (Monday)
Tues. (Tuesday)
Thurs. (Thursday)
Ave. (Avenue)
St. (Street)
i.e. (id est = in other words)
e.g. (exempli gratia = for example)
etc. (et cetera = and so forth)
Fla. (Florida)
Mont. (Montana)
No Periods
Days of the Week: Two- or Three-Letter Abbreviations Directions
(all caps)
US Postal Abbreviations
(all caps)
Tu or Tue (Tuesday) NW (northwest)
SE (southeast)
FL (Florida)
MT (Montana)

Note: Three-letter abbreviations for days of the week can be written with or without a period at the end. Whether you decide to use periods or not, just remember to be consistent in your writing.

Tue. and Wed.
Tue and Wed


Most measurements and scientific abbreviations do not use periods, but standard United States measurements and time abbreviations have a period at the end.

Standard US Measurements Time Abbreviations
in. (inch)
ft. (foot)
oz. (ounce)(The z in oz. comes from the Medieval Italian word onza.)
sec. (second)
h. or hr. (hour)
No Periods
Metric Measurements Math and Science Computer and Internet
ml (milliliter)
km (kilometer)
cg (centigram)
mph (miles per hour)
mpg (miles per gallon)
rpm (revolutions per minute)
CPU (central processing unit)
URL (uniform resource locator)
DVD (digital video disc)

Abbreviations in All Capitals

Abbreviations made up of the first letter of each word in a phrase, usually in all capitals, do not generally use periods, with some exceptions here and there.

(Exception to the Above Rule)
The Abbreviation for District of Columbia
Washington, D.C.
(D.C. has periods even though it is pronounced letter by letter.)
No Periods
(The Norm)
Acronyms Abbreviations Pronounced Letter by Letter
These are abbreviations pronounced as words instead of a string of letters. Some acronym abbreviations have actually become words themselves.
NASA (National Aeronautics and Space Administration)
NATO (North Atlantic Treaty Organization)
FBI (Federal Bureau of Investigation)
FYI (for your information)
MVP (most valuable player)

Abbreviations that Can Go Either Way

Some abbreviations are rapidly changing. Either form is generally accepted, but check with your teacher or style manual to make sure.

Acceptable With or Without Periods
U.S.A. or USA
B.C., A.D., C.E., B.C.E. or BC, AD, CE, BCE
(B.C. or BC: Before Christ; A.D. or AD: Anno Domini; C.E. or CE: Common Era; B.C.E. or BCE: Before Common Era)
a.m., p.m. or AM, PM
If lowercase, use periods. If capitals, do not use periods.
(a.m. or AM: ante meridiem/before midday; p.m. or PM: post meridiem/after midday)

Abbreviations and End Punctuation

If you end a sentence with an abbreviation containing a period, do not put another period at the end of the sentence. However, if a sentence ends in an exclamation mark or a question mark, include both the abbreviation's period and the end mark.

His son's name is Jason Miller Jr. (abbreviation period only, no end period)
Is his son's name Jason Miller Jr.? (abbreviation period + ending question mark)

Practice What You've Learned

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One or more periods have been omitted from each of the following sentences. To insert a period, click the space after the abbreviation, or after each letter in the abbreviation. Some sentences have more than one abbreviation. Some abbreviations have a space after them or a space after each letter, but you have to decide whether periods are required or not.
For this class you will need to read two classic novels, e.g. Little Women, Gone with the Wind, Uncle Tom's Cabin, etc..
My dream is to work in Washington, D.C. at the F.B.I. headquarters.
Your next appointment with Dr. Mason is Feb. 19 at 3:00 P.M..
Please complete questions 1-5 on p. 27.
Which weighs more, 3 kg. or 3 lbs.?
Capt. J. J. Michaels opened a new business-Security, Inc. -which rents out guard dogs.
Instead of collecting candy at Halloween, we spent 30 min. collecting money for U.N.I.C.E.F. , the international children's charity.
Jr., my little brother, kept putting sandwiches in the V.C.R., and I wonder what he will put in the new D.V.D. player, cookies?
If he was born at 12 a.m. on Dec. 31, was he born in 1999 or 2000?
The city of St. Louis is in K.Y., while East St. Louis is in Ill. on the other side of the river.