As a general rule, you should avoid abbreviations in formal writing unless you are sure that the abbreviations you are using will be familiar to your audience. The situation is somewhat different in scientific and technical writing. Depending on your specific field, it may be acceptable or even preferable to use agreed upon abbreviations for complex terms.
English punctuation and capitalization rules for abbreviations vary widely because those rules frequently change, with variations occurring even between American and British English.
The current trend is to write abbreviations without periods. However, it is acceptable to write many abbreviations with or without periods:
PhD or Ph.D. BA or B.A.
USA or U.S.A. PM or P.M. OR p.m.
Abbreviations composed of all capital letters almost never have periods or spaces between letters:
PIN (Personal Identification Number)
TEI (The English Island)
Abbreviations composed of or ending in lowercase letters usually have a period at the end but not in between letters:
One notable exception to the above rule is abbreviations for units of measure:
mph (miles per hour)
Titles of People
You should always abbreviate titles that appear before or after people’s names. Certain titles always go before a person’s name:
Other titles go after a person’s name:
Megan Santiago, RN (R.N.)
Sammy Davis Jr.
Allison Henderson, CPA (C.P.A)
Jaime Gonzales, Esq.
Those with doctorates can have a title either before or after their names:
Dr. Grace Lin OR Grace Lin, DDS (D.D.S.)
Dr. Hector Rodriguez OR Hector Rodriguez, MD (M.D.)
Dr. Sally Yoder OR Sally Yoder, PhD (Ph.D.)
While the rules for using periods and commas with an abbreviation may be confusing (or whether to use an abbreviation at all!), you can master these and other tricky English grammar and vocabulary with time and practice. If you need help with grammar, pronunciation, or abbreviations, the dedicated teachers at the English Island in Atlanta can help improve your skills through a variety of individual or small group ESL classes designed for students of all levels.