The BOY Diphthong /ɔɪ/

One of the most common diphthongs in American English. Hear it in boy, toy, oil, joy.

IPA /ɔɪ/ Respell oy Category Diphthong
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The /ɔɪ/ diphthong, the sound in boy, toy, oil, coin, is a two-part gliding vowel that moves from a rounded back position to a relaxed front one. You start with lips noticeably rounded and the tongue pulled back, almost like you're saying AW. Then glide smoothly: jaw rises, lips relax, the front of the tongue arches forward toward an /ɪ/ shape. The big lip-shape change between the two halves is what gives BOI its bouncy, two-beat feel.

How to make it

Three small adjustments.

Get them right and the sound takes care of itself.

Start with rounded lips and tongue shifted back. Glide to relaxed lips with the tongue arching forward and up.

First position of /ɔɪ/ in boy
Second position of /ɔɪ/ in boy

Mouth shape

/ɔɪ/ as in boy

Jaw

Drops for the start, comes back up for the end.

Tongue

Lightly lifted and shifted back in the first position (tip not touching anything). For the ending, the tongue comes forward with the tip touching the back of bottom front teeth and the top-front arching up.

Lips

Rounded for the first position (more than the pure AW vowel). Relaxed for the second position.

Hear it in words

16 everyday words.

Tap any word for its full breakdown — every reduction, every flap-T.

boy
BOY
joy
JOY
coin
KOYN
voice
VOYS
noise
NOYZ
choice
CHOYS
point
POYNT
join
JOYN
oil
OYL
soil
SOYL
toy
TOY
avoid
uh·VOYD
annoy
uh·NOY
loyal
LOY·uhl
appointment
uh·POYNT·muhnt
employer
ehm·PLOY·er
Hear it in sentences

In real conversation.

5 short sentences where this sound shows up. Tap to play; click the title for the full breakdown.

The boy has a toy.

dhuh BOY huhz uh TOY.

Point to the coin.

POYNT tuh dhuh KOYN.

Do not annoy the boy.

doo NAHT uh·NOY dhuh BOY.

Avoid the poison and enjoy the choice oil.

uh·VOYD dhuh POY·zuhn and uhn·JOY dhuh CHOYS OYL.

The royal boy enjoyed the joy of the toy.

dhuh ROY·uhl BOY uhn·JOYD dhuh JOY uhv dhuh TOY.
FAQ

Common questions about /ɔɪ/.

What is the exact mouth movement for the /ɔɪ/ vowel?
Start by dropping your jaw slightly and rounding your lips, with the tongue pulled back. From this rounded starting point, glide smoothly into the second shape: raise the jaw, relax the lips completely, and bring the tongue forward so the tip rests behind the bottom front teeth. The key is making sure both halves of the glide are fully pronounced, especially in stressed words like boy or joy.
Why does my /ɔɪ/ sound clipped or flat to American ears?
You're probably using a tight, static starting vowel and rushing into the second half. A lot of learners skip the strong lip rounding at the start, so the sound slides too quickly toward /ɪ/. Plant a real, rounded AW shape first, hold it for a beat, then glide to a relaxed /ɪ/ ending. Rush the transition and words like coin or point lose their two-part feel.
Why is /ɔɪ/ before an L hard, like in "oil" or "boil"?
The American dark L pulls the tongue back, which fights the forward, relaxed ending of /ɔɪ/. The fix: add a tiny invisible Y glide between the vowel and the L. Think of oil as OY-yuhl, boil as BOY-yuhl. Splitting the word into two syllables gives the tongue time to finish the fronted vowel before pulling back for the dark L.

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