Biannual vs. Biennial: Twice a Year or Every Two Years?

The Distinction

• Biannual = twice a year (every six months)
• Biennial = once every two years

Using Biannual

“Biannual” events happen two times per year:

• “The company holds biannual reviews in June and December.” ✓
• “We publish a biannual newsletter.” ✓
• “The biannual sale happens in spring and fall.” ✓

Synonym: semiannual

Using Biennial

“Biennial” events happen once every two years:

• “The biennial conference takes place in even-numbered years.” ✓
• “Venice hosts a biennial art exhibition.” ✓
• “Biennial plants complete their life cycle in two years.” ✓

Why the Confusion?

The prefix “bi-” can mean either “two” or “twice,” which creates ambiguity. This is why many style guides recommend avoiding these words altogether.

Clearer Alternatives

Instead of risking confusion:

• Biannual → “twice a year” or “semiannual”
• Biennial → “every two years”

Memory Trick

• Biannual has two N’s = happens twice in one year
• Biennial sounds like “perennial” = think of longer time cycles