Capitalization of Acronym Expansions
Capitalization of Acronym Expansions explains Microsoft’s rule that acronym letters do not by themselves justify capitalizing the spelled-out words.
Do not capitalize a spelled-out acronym expansion just to match the acronym’s capitals; keep ordinary words lowercase unless they are proper nouns.
Key details
Important caveats
Scope Boundary
This is a capitalization rule for ordinary expansions, not a direction to lowercase official proper names.
Further guidance
Content
Lowercase ordinary words in a spelled-out acronym expansion; retain capitalization required by proper nouns.
Practical Application
Spell out an acronym using normal capitalization for the underlying phrase. Do not capitalize ordinary common nouns merely because their initial letters form an uppercase acronym; retain capitals only for proper names or other independently capitalized elements.
Purpose
Avoid false title-style capitalization created only to mirror an acronym’s uppercase letters.
Reader Check
If the acronym were removed, would each capital in the expansion still be justified?
Worked Example
Write “application programming interface (API),” not “Application Programming Interface (API),” unless the expansion itself is an official proper name.
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.
- Acronyms checklist — Microsoft Style Guide (opens in a new tab)Microsoft · Microsoft technical-style checklist for first-use acronym expansion and capitalization of spelled-out forms
- Capitalization — Microsoft Style Guide (opens in a new tab)Microsoft · Microsoft technical-style guidance for sentence-style headings, acronym expansion capitalization and capitalization after colons