Numbers trip learners up more than they should, and the culprit is often the /tw/ cluster at the start of twelve, twenty, and twin. The fix is one small move: after the T, round your lips for a quick W before the vowel arrives.
The Rule
The letters TW represent two sounds pronounced together: /t/ + /w/. Tap the tongue for a crisp T, and at the same moment push your lips into a small circle for the W glide, then open into the vowel. Do not insert a vowel between them ("tuh-welve") and do not drop the W ("telve"). This blend opens a family of everyday words: twelve, twenty, twin, twist, twice, twig, tweet, twinkle, tweezers, between, twenty-two. Keep it fast and smooth: t-w-elve.
Practice Words
The Silent-W Exception: Two
The number two is spelled with TW but pronounced simply /tuː/, with a completely silent W. The spelling is a historical fossil that links it to its cousins twin, twice, and twelve, where the W is alive. A couple of other words also hide a silent W after a consonant: sword /sɔːrd/ and answer /ˈænsər/. But apart from these fixed exceptions, TW at the start of a word is always the full /tw/ blend.
Quick Tip
Practice the minimal contrast to and two (identical: /tuː/) against twin and twist (lips rounded early). Feeling your lips round before twin but stay relaxed for two locks in the difference.