General Guidelines:
* Numbers 0-9: Spell these out in full (one, two, three, etc.).
* Numbers 10 and above: Use numerals (10, 11, 12, etc.).
* Exceptions:
* Start of a sentence: Always spell out numbers that start a sentence.
* Informal writing: You may sometimes spell out numbers 10-100 in informal contexts.
* Fractions: Usually spelled out (one-half, two-thirds, etc.).
* Mixed numbers: Combine numerals and words (1 and 1/2, 2 and 2/3, etc.).
Specific Situations:
* Years: Use numerals (2023, 1984).
* Addresses: Use numerals (123 Main Street).
* Dates:
* Days: Use numerals (January 1, June 15).
* Years: Use numerals (1999, 2024).
* Decades: Use numerals and hyphens (1980s, 2010s).
* Time:
* Hours and minutes: Use numerals (8:00 AM, 3:15 PM).
* O'clock: Spell out "o'clock."
* Money: Use the dollar sign and numerals ($10, $25.50).
* Percentages: Use numerals and the percent sign (5%, 100%).
Consistency is Key:
* Be consistent within a single piece of writing. If you choose to spell out numbers 10-100, do so throughout.
* Follow style guides (like APA, MLA, Chicago) if writing for a specific purpose.
Ultimately, the best way to know the "right" way to spell out numbers is to consider the context and your audience.