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    Punctuation Rules for Periods in Written English

    Punctuation Rules for Periods in Written English

    Punctuation marks are a convention of written language that ensure the clarity of writing. There are five punctuation rules for using periods as punctuation marks in written American English:

    • Sentence endings
    • Decimal points
    • Abbreviations
    • Computer files and Internet addresses
    • Play and poetry citations

    The following sections explain and provide examples of the punctuation rules for periods in written English.

    Ending Sentences

    PeriodUse a period at the end of most declarative sentences. A declarative sentence is a sentence that makes a statement. For example:

    • The pumpkins molded in the garden.
    • A noun has traditionally been defined as a word that names person, place, or thing.
    • Cartoon Network is a popular television channel.
    • My son ate all the cookies.

    Use a period at the end of an imperative sentence that does not convey strong emotion. An imperative sentence is a sentence that makes direct commands, expresses requests, and grants or denies permission. For example:

    • Please open the window.
    • Bring a dessert to dinner tomorrow night.
    • Wash your hands before eating.
    • Press the blue button to print.

    In general, most sentences in written English end with a period.

    Decimal Points

    Use a period as a decimal point to mark the boundary between an integral from the fractional part of a number. An integral is the whole number on the left side of a decimal point. A fraction is the number on the right side of a decimal point. For example:

    • 1.5
    • 3.14
    • 13.375
    • 8,652.3

    Use a period to separate dollars from cents when writing about money in American English. For example:

    • $1.99
    • $0.25
    • $175.03
    • $2,675.17


    Use a period with most abbreviations including abbreviated titles, times, and words. For example:

    • Barty Crouch, Jr.
    • Ms. Johnson
    • 5:00 p.m.
    • c. (circa)
    • Apr. (April)

    Do not use a period with state or most organizational abbreviations. For example:

    • LA (Louisiana)
    • OR (Oregon)
    • NASA (National Aeronautics and Space Administration)
    • NATO (North Atlantic Treaty Organization)

    Note that some style guides require slightly different rules for the use of periods with abbreviations.

    File Names and Internet Addresses

    Use a period to separate the name of a computer file from the file extension. A file extension identifies the type of file that a computer file is. For example:

    • englishpunctuationrules.doc
    • puppy.jpg
    • bluewaterfall.css
    • fireflies.mp3

    Use a period to separate elements of Internet addresses including URLs and email addresses. For example:


    Drama and Poetry Citations

    Use a period to separate book, line, act, and scene elements in drama and poetry citations. Place a period between the acts and scenes of a prose play and between the acts, scenes, and lines of a verse play. For example:

    • For Whom the Seagulls Fly 1.3 (act.scene)
    • Contradiction in a Square Degree 2.2 (act.scene)
    • Faust 1.1.125 (act.scene.line)
    • A Midsummer’s Night Dream 2.1.365 (act.scene.line)

    Place a period between the books and lines of a poem. For example:

    • Iliad 2.45 (book.line)
    • The Faerie Queene 4.654 (book.line)
    • Song of Myself 1.34-38 (book.lines)
    • Aurora Leigh 9.12-35 (book.lines)

    Punctuation is a convention of writing that help readers more clearly understand written language. Periods perform five basic functions in written American English: end sentences, as decimal points, abbreviations, electronic files and Internet addresses, and poem and drama citations.


    Faigley, Lester. 2003. The Brief Penguin Handbook. New York: Pearson Longman.
    Gibaldi, Joseph. 2003. MLA Handbook for Writers of Research Papers. 6th ed. New York: The Modern Language Association of America.

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