'Semiannual' vs 'Biannual': What's the Difference?

By Katie Moore, updated on July 10, 2023

‘Semiannual’ vs ‘Biannual’: What’s the Difference? The debate about the difference between these two words has become quite the fight due to the fact that they each have both overlapping and separate meanings. Want to enter the arena? In this article, we’ll give you all the information you need to choose your fighter. 

In a rush? Here’s a quick version of what you’ll read: 

  • ‘Semiannual’ refers to something that happens every half a year. 
  • ‘Biannual’ refers to something that happens every two years. 
  • Both words can refer to something that happens twice a year. 

What’s the Difference Between ‘Semiannual’ vs ‘Biannual’?

The problem that most people encounter when using these words is that, in some cases, both terms are correct and mean the same thing.

  • ‘Semiannual’ and ‘Biannual’ can both mean “twice a year.”

So, when you’re referring to something that happens two times in the same year, you can use both ‘Semiannual’ and/or ‘Biannual’ to refer to it. 

However, each word also has its own other meaning which is often what ends up sparking debate. As mentioned above, ‘Biannual' can also refer to something that happens every two years. In contrast, ‘Semiannual’ can refer to something that happens every half a year or over a period of six months. 

The key to understanding and identifying the difference here? Prefixes. Let’s take a closer look at the individual meanings of ‘Semiannual’ vs ‘Biannual’ to gain some clarity. 

Definition of ‘Semiannual’: What Does it Mean? 

According to Oxford Languages, ‘Semiannual’ is an adjective meaning: 

  • Occurring twice a year; half-yearly
  • (of a plant) living for half a year only

The secondary definition, “half-yearly,” is what we want to focus on here because it links us to the history of this word. The defining factor of both words in question today is their prefixes, in this case, the “semi-” in ‘Semiannual.’ 

Phrases with ‘Semiannual’

  • Semiannual sale
  • Semiannual promotion
  • Semiannual review

According to The Dictionary, ‘semi-’ is a prefix meaning: 

  • Half
  • Partly, somewhat, less than fully

Knowing that ‘semi-’ refers to something incomplete helps remind us that a ‘Semiannual’ event occurs twice in one year. Additionally, since ‘semi-’ refers to half of something, we see how it can correlate to just half of the year. 

Phrases with ‘Semi-’

  • Semicircle 
  • Semifinal 
  • Semiconscious

One final thing to note is that ‘Semiannual’ things don’t have to occur at the exact mid and endpoints of a year — they can occur in any range of time as long as it’s twice within one year. 

Definition of ‘Biannual’: What Does It Mean?

According to Merriam-Webster, ‘Biannual’ is an adjective meaning: 

  • Occurring twice a year
  • Occurring once every two years

Note that an important distinction must be made here. While it is often unused in American English, the word ‘Biennial’ is another form of ‘Biannual’ that exclusively means: 

  • Happening once every two years

The issue of this mainly comes down to pronunciation and the uncommonness of ‘Biennial’ leading to its essential extinction in most writing and especially conversation. But, it is nonetheless important to know

Phrases with Biannual

  • Biannual event
  • Biannual meeting
  • Biannual raise

Returning to prefixes, what sets both versions of this word apart is the prefix ‘bi-.’ According to The Dictionary, ‘bi-’ is a prefix meaning: 

  • A combining form meaning ‘twice’ or ‘two.’
  • On both sides (used in the formation of compound words)

The ‘twice’ in the definition makes it possible to use this word to mean ‘twice a year.’ Yet the ‘two’ in the definition is what gives this word its other meaning of ‘every two years.’ 

Phrases with ‘Bi-’

  • Bisexual
  • Bilateral
  • Bifocal
  • Biplane

Pronunciations: How to Pronounce ‘Semiannual’ vs ‘Biannual’

Knowing when to use the words is only half the battle; we want you to be able to say them properly too. Also, since ‘semi-’ and ‘bi-’ are such common prefixes, you’ll be able to transfer parts of these pronunciations to other new words you learn. 

Use this phonetic spelling of ‘Semiannual’ as a guide:

‘Seh-mee-an-yoo-uhl’ (with the “an” as in ‘sand’)

Use this phonetic spelling of ‘Biannual’ as a guide: 

‘By-an-yoo-uhl’ (with the “i” as in ‘fly’)

Finally, to avoid confusion, use this phonetic spelling of ‘Biennial’ as a guide:


How to Use ‘Semiannual’ vs ‘Biannual’ in a Sentence

To help clarify that these words can both mean the same thing and still have their separate meanings, here are some example sentences you can use as references. They may also help prepare you for when you encounter this dispute in your own conversations. 


  • The semiannual office party is always more fun in December as opposed to June. 
  • The boss comes in for our semiannual performance review twice a year. 
  • I bought these semiannual plants because I am moving in six months. 
  • I always bank on the semiannual sales in March and September. 


  • With the Winter and Summer Games going now, the Olympics occur biannually
  • The biannual promotion system means we move up every two years. 
  • We do our family reunion on a biannual schedule so we don’t get overwhelmed. 
  • I went to the biannual super sale at the store this week because it won't come again for another six months. 

Final Advice on ‘Semiannual’ vs ‘Biannual’

While the debate may continue, you are now equipped to join the winning side in any situation. Words with overlapping meanings can be confusing, especially when pronunciations get thrown into the mix, but if you take special care to notice prefixes, you’ll do just fine. 

Here is a quick review of what we covered: 

  • Both ‘Semiannual’ and ‘Biannual’ can mean “twice a year,”
  • But if you pay attention to the prefix ‘semi-’ meaning “half,” you know that ‘Semiannually’ also means occurring every half a year.
  • Meanwhile, the prefix ‘bi-’ means “two,” which can help you remember that ‘Biannual’ also means every two years. Note that ‘Biennial’ also means every two years but is much less commonly used.

Be sure to check out more confusing word articles to stay sharp and feel confident entering other grammar debates. You can also read more about prefixes to expand your vocabulary and your knowledge of language history. 

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Written By:
Katie Moore
Katie is a recent graduate of Occidental College where she worked as a writer and editor for the school paper while studying linguistics and journalism. She loves helping others find their voice in writing and making their work the strongest it can be. Katie also loves learning and speaking other languages and wants to help make writing accessible for everyone.

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