Most people learn that an goes before vowels. That's almost right, and the "almost" is where the mistakes happen.

The short answer #

The choice depends on the first sound of the next word, not its first letter.

Use Before Example
a a consonant sound a book, a user, a one-time fee
an a vowel sound an apple, an hour, an MBA

Why "an hour" but "a house" #

In hour, the h is silent, so the word starts with a vowel sound: an hour, an honest mistake.

In house, you pronounce the h: a house, a hotel.

Why "a university" but "an umbrella" #

University starts with a y sound (you-niversity), which is a consonant sound: a university, a unique idea, a European trip.

Umbrella starts with a vowel sound: an umbrella, an update.

Abbreviations #

Say the abbreviation out loud and listen to the first sound.

  • an FAQ page (eff-), an SMS, an MBA
  • a URL (you-), a UFO, a NASA project (nass-)

Adjectives change the choice #

The article matches the word right after it, even if it's an adjective.

  • an apple → a red apple
  • a hard task → an easy task

Common mistakes #

Wrong Right
an user a user
a hour an hour
a honest answer an honest answer

Let AI handle it #

AI Grammar Checker listens to the sentence the way a reader would, and picks a or an for you.