Writing & StyleStyle guide
Writing Age: 5-year-old vs. 5 Years Old
Hyphenate an age when the age phrase works as a compound modifier before a noun or as a noun itself: “a 5-year-old child” or “a 5-year-old.” Leave the phrase open after a linking verb: “the child is 5 years old.”
Write “a 5-year-old child” and “a 5-year-old,” but “the child is 5 years old.” The grammatical role determines the hyphens.
Key details
Attributive Form5-year-old child
Core Issuehyphenation of age expressions
Nominal Forma 5-year-old
Predicative Form5 years old
Important caveats
Predicative Boundary
Do not hyphenate the ordinary “years old” phrase after the noun or linking verb: “She is 5 years old.”
Further guidance
Modifier Rule
Use hyphens to bind the age phrase when it modifies a following noun or stands as a noun phrase.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Hyphens, En Dashes, Em Dashes — age terms Q&A (opens in a new tab)The Chicago Manual of Style · Chicago guidance on hyphenating age expressions when attributive or nominal, versus open predicative age phrases