Spelling rule
oi or oy: where each spelling goes
The answer
Use oi inside a word or syllable (coin, boil, avoid) and oy where a word or syllable ends (toy, enjoy, loyal). Our lexicon has 43 base words that follow this and 2 that break it.
When does the rule apply?
The oi and oy rule is the same position rule as ai and ay, and students who know one pick up the other in a day. The /oi/ sound is a diphthong: the mouth glides from one vowel to another inside a single syllable. When it falls at the end of a word or right before another vowel sound (loy-al, roy-al), the spelling is oy. When a consonant follows it in the same syllable, it is oi: join, point, moist.
Words that follow the rule
oi inside a syllable
| Word | Position | Readable after |
|---|---|---|
| oil | oi inside the syllable | Lesson 95 |
| join | oi inside the syllable | Lesson 95 |
| joint | oi inside the syllable | Lesson 95 |
| noise | oi inside the syllable | Lesson 95 |
| point | oi inside the syllable | Lesson 95 |
| voice | oi inside the syllable | Lesson 95 |
| choice | oi inside the syllable | Lesson 95 |
| avoid | oi inside the syllable | Lesson 95 |
| boil | oi inside the syllable | Lesson 95 |
| coin | oi inside the syllable | Lesson 95 |
| soil | oi inside the syllable | Lesson 95 |
| void | oi inside the syllable | Lesson 95 |
| spoil | oi inside the syllable | Lesson 95 |
| devoid | oi inside the syllable | Lesson 95 |
| poison | oi inside the syllable | Lesson 95 |
| toilet | oi inside the syllable | Lesson 95 |
| appoint | oi inside the syllable | Lesson 95 |
| exploit | oi inside the syllable | Lesson 95 |
| paranoid | oi inside the syllable | not taught |
| exploitation | oi inside the syllable | Lesson 119 |
| coil | oi inside the syllable | Lesson 95 |
| foil | oi inside the syllable | Lesson 95 |
| loin | oi inside the syllable | Lesson 95 |
| toil | oi inside the syllable | Lesson 95 |
| broil | oi inside the syllable | Lesson 95 |
| foist | oi inside the syllable | Lesson 95 |
| hoist | oi inside the syllable | Lesson 95 |
| moist | oi inside the syllable | Lesson 95 |
| poise | oi inside the syllable | Lesson 95 |
| invoice | oi inside the syllable | Lesson 95 |
oy at the end of a word or syllable
| Word | Position | Readable after |
|---|---|---|
| boy | oy at the end | Lesson 95 |
| joy | oy at the end | Lesson 95 |
| annoy | oy at the end | Lesson 95 |
| enjoy | oy at the end | Lesson 95 |
| destroy | oy at the end | Lesson 95 |
| employee | oy ends a syllable | Lesson 95 |
| toy | oy at the end | Lesson 95 |
| ploy | oy at the end | Lesson 95 |
| loyal | oy ends a syllable | Lesson 95 |
| royal | oy ends a syllable | Lesson 95 |
| employ | oy at the end | Lesson 95 |
| annoyance | oy ends a syllable | Lesson 95 |
| coy | oy at the end | Lesson 95 |
Words that break the rule
oy where the rule expects oi
| Word | Why it breaks | Readable after |
|---|---|---|
| unemployment | oy inside the syllable | Lesson 95 |
oi where the rule expects oy
| Word | Why it breaks | Readable after |
|---|---|---|
| paranoia | oi ends a syllable | not taught |
How do you teach it?
Pair it with ai and ay. Ask students to predict: if ai goes in the middle and ay at the end, where do oi and oy go? Then dictate a mixed set: coin, toy, soil, enjoy, voice, annoy.
"Spell 'destroy'. Where's /oi/? At the end. Nothing after it, so o-y. Now 'moist'. /oi/, then /s/ and /t/. Consonants come after it, so it's o-i."
What is the common error, and the fix?
"Boi" and "toyl" are the errors, and they show a student who spells the sound but ignores its position. Ask whether anything comes after /oi/ in the syllable. A consonant means oi; nothing means oy.
Sort it: a hands-on activity
Mix oi and oy cards with the ai and ay cards from the matching page. Students sort into a two-by-two grid, middle and end, by sound. The grid makes the shared pattern obvious.
How this list was built
Every word comes from our lexicon of about 19,000 common words, each checked against a pronouncing dictionary and split into spelling units. Words a student meets in our assessments and progress-monitoring probes are left out, so practicing a list never rehearses a test. Rule groups are computed from each word's spelling units and its word sum (base plus suffix), then checked by hand; false word sums such as man + er for manner are removed.
"Readable after" is the first lesson in the lesson sequence at which our decodability engine finds every sound-spelling in the word taught; "not taught" means the word has a spelling the sequence does not cover, so it is read with help. You can check your own lists and passages with the free decodable text checker.
Questions people ask
Why do royal and loyal use oy if the sound is in the middle?
The oy ends its syllable: roy-al, loy-al. The next syllable starts with a vowel sound. The rule covers the end of any syllable, and a word's last letter is just one case.
What are the exceptions?
Our list finds 2: unemployment, paranoia. When a suffix is added, oy can end up in the middle of a longer word (enjoyment, employer), and the base word still follows the rule.
Are oi and oy vowel teams or diphthongs?
Both labels are used. The sound is a diphthong, a glide between two vowel sounds, and the spellings are vowel teams.