With numbers. The following abbreviations are all acceptable with specific years and times.

399 bce (“before the common era”) or 399 bc (“before Christ”)

49 ce (“common era”) or ad 49 (anno Domini, Latin for “year of our Lord”)

11:15 am (or a.m.)

9:00 pm (or p.m.)

Symbols such as % and $ are acceptable with figures ($11) but not with words (eleven dollars). Units of measurement can be abbreviated in charts and graphs (4 in.) but not in the body of a paper (four inches).