16. Dates, decades and centuries

Dates: Use Arabic figures without st, nd, rd or th. Year is set off by commas when preceded by month and date (The policy will take effect Jan. 1, 2019, and will apply to all staff); no commas with month/season and year only (January 2020, summer 2017). When a month is used with a specific date, abbreviate only Jan., Feb., Aug., Sept., Oct., Nov. and Dec.; spell out months when using alone or with year alone.

Decades: Use Arabic figures for decades of history; use an apostrophe to indicate numerals that are left out: the 1990s, the ’90s.

Centuries: Lowercase and spell out numbers less than 10: the first century, the 20th century. Hyphenate when used as modifier: 18th-century Germany.