Often: hay before the verb, and có hay … không?

Hay before a verb means "often": Cuối tuần tôi hay đi bơi. I often go swimming at weekends. It's the everyday spoken word, a little more casual than thường (usually), and it sits in the same place, right before the verb.

It's also how people talk about habits, good or bad: Em hay quên. I'm always forgetting things.

To ask how often, put có hay before the verb and không at the end: Em có hay đi Vũng Tàu không? Do you go to Vũng Tàu often? Answer Có or Không, or with thỉnh thoảng (sometimes) or ít khi (rarely). Không hay means "not often": Tôi không hay nấu ăn. I don't cook much.

Hay has two other meanings, and its place tells them apart. Describing a noun, it means "good, interesting": Phim này hay quá! This film is so good! After a verb, it means "well": Cô ấy hát hay (she sings well), but Cô ấy hay hát (she often sings). Between two choices in a question, it means "or": Trà hay cà phê? Tea or coffee?