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1. A.D., B.C. Small caps, periods, no space. A.D. precedes year and is used only when era might be in doubt: Augustus died in A.D. 14; June, A.D. 52; the first century A.D. The term B.C. follows the year: 2500 B.C., 12,000 B.C. Use comma with five digits or more.

An alternative system gaining popularity, especially in academic literature, uses C.E. (meaning the Common Era and used in place of A.D.) and B.C.E. (before the Common Era). National Geographic generally uses the traditional terms, A.D. and B.C.

2. BP Small caps, no periods or space; should be explained if used. A date expressed as "11,000 BP" means 11,000 years before the present, using 1950 as the benchmark. Use comma with five digits or more. The older date should come first: 47,000 to 43,000 BP.

3. Plus or minus Spell out: plus or minus 50 years.

4. Days and months Not abbreviated in text or legends. In footnotes and map notes, months and days may be abbreviated for lack of space:
    on March 1, 1978, they . . . not March 1st, 1978, they
the first of March 1978 (no commas)
in March 1978 we . . . (no commas) not in March of 1978 we . . .
on Sunday, January 30, 1972, they
the tenth of March (spell out through tenth if the date precedes the month)
the second of March, but March 2
the 22nd of March, but March 22
22 March 1986 (avoid if possible)
Christmas Day, 1980, was . . .
In spring 1979 we . . .
the Fourth of July, 1776, was . . .

5. Decades Generally spelled out when the century is not given. When century is given, use figures. Write: the 1960s (sometimes the '60s)
    the eighties
the Gay Nineties
the Roaring Twenties
but the "apathetic" fifties

the 1930s and '40s, the mid-thirties, mid-1940s, but not mid-'40s
the twenties
the 1890s style, 1890s-style dress
6. Centuries Spell out first through ninth century (lowercase): the second century A.D., the 12th century B.C., 20th, 22nd, 23rd, etc. Note that both A.D. and B.C. follow the century. Hyphenate as a compound adjective before a noun: 12th-century artist, second-century B.C. vase, late 18th-century house.

7. Inclusive dates A hyphen means up to and including when used between dates: November 15-21; 1941-45. When using from, do not use a hyphen but spell out to or through and give complete date: from 1941 through 1945. With hyphen use only the last two digits except where three zeros would come together or decades are different: 1962-65, 1900-1901, 1804-06, 1900-1910, 1949-1950, 1941-1963. Never use one digit alone in a date: 1947-49 not 1947-9.

When giving a range of B.C. years, always use complete numbers: 189-188 is not the same as 189-88.

8. Miscellaneous It is preferable to give specific date: in 1887, not 99 years ago. Years and centuries are lowercase when spelled out.