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Hindustani natively possesses a symmetrical ten-vowel system.^[1] The vowels: [ə], [ɪ], [ʊ] are always short in length, while the vowels: [aː, iː, uː, eː, oː, ɛː, ɔː] are always considered long (but see the details below). Among the close vowels, what in Sanskrit are thought to have been primarily distinctions of vowel length (that is/i ~ iː/ and /u ~ uː/), have become in Hindustani distinctions of quality, or length accompanied by quality (that is, /ɪ ~ iː/ and /ʊ ~ uː/).^[2] The historical opposition of length in the close vowels has been neutralized in word-final position, for example Sanskrit loans śakti (शक्ति – شَکتی 'energy') and vastu (वस्तु – وَستُو 'item') are /ʃəkt̪i/ and /ʋəst̪u/, not */ʃəkt̪ɪ/ and */ʋəst̪ʊ/.^[3]

/ə/ is often realized more open than mid [ə], i.e. as near-open [ɐ].^[4]

The vowel represented graphically as ऐ – اَے (Romanized as ai) has been variously transcribed as [ɛː] or [æː].^[5] Among sources for this article, Ohala (1999), pictured to the right, uses [ɛː], while Shapiro (2003:258) and Masica (1991:110) use [æː]. Furthermore, an eleventh vowel /æː/ is found in English loanwords, such as/bæːʈ/ ('bat').^[6] Hereafter, the former will be represented as [ɛː] to distinguish it from the latter. The open central vowel is transcribed in IPA by either [aː] or [ɑː]. Despite this, the Hindustani vowel system is quite similar to that of English, in contrast to the consonants.

In addition, [ɛ] occurs as a conditioned allophone of /ə/ (schwa) in proximity to /h/, if and only if the /h/ is surrounded on both sides by two schwas.^[7] For example, in /kəɦ(ə)naː/ (कहना – کَہنا 'to say'), the /h/ is surrounded on both sides by schwa, hence both the schwas will become fronted to short [ɛ], giving the pronunciation [kɛɦ(ɛ)naː]. Syncopation of phonemic middle schwa can further occur to give [kɛɦ.naː]. The fronting also occurs in word-final /h/, presumably because a lone consonant carries an unpronounced schwa. Hence, /kəh(ə)/ (कह – کَہہ 'say!') becomes [kɛh] in actual pronunciation. However, the fronting of schwa does not occur in words with a schwa only on one side of the /h/ such as /kəhaːniː/ (कहानी – کَہانی 'a story') or /baːhər/ (बाहर – باہَر 'outside').

As in French and Portuguese, there are nasalized vowels in Hindustani. There is disagreement over the issue of the nature of nasalization (barring English-loaned /æ/ which isn't nasalized^[6]). Masica (1991:117) presents four differing viewpoints:

1. there are no *[ẽ] and *[õ], possibly because of the effect of nasalization on vowel quality;
2. there is phonemic nasalization of all vowels;
3. all vowel nasalization is predictable (i.e. allophonic);
4. Nasalized long vowel phonemes (/ĩː ẽː ɛ̃ː ɑ̃ː ɔ̃ː õː ũː/) occur word-finally and before voiceless stops; instances of nasalized short vowels ([ɪ̃ ə̃ ʊ̃]) and of nasalized long vowels before voiced stops (the latter, presumably because of a deleted nasal consonant) are allophonic.