Suniti Kumar Chatterji and Sukumar Sen classified Bengali dialects in five classes by their phonology and pronunciation.
It is spoken across the Khulna, Barisal, Dhaka, Mymensingh, Sylhet and Comilla Divisions of Bangladesh and the State of Tripura in India.
Formal spoken Bengali, including what is heard in news reports, speeches, announcements, and lectures, is modelled on Choltibhasha.
During standardisation of Bengali in the late 19th and early 20th centuries, the cultural elite were mostly from the regions of Dhaka, Kolkata, Hooghly, Howrah, 24 Parganas, Nadia and Kushtia.
What is accepted as the standard form today in both West Bengal and Bangladesh is based on the West-Central dialect.
Mostly speech varies across distances of just a few miles and takes distinct forms among religious communities.
These dialects are mostly spoken in and around the Bhagirathi River basin, in Central West Bengal and Southwestern Bangladesh .
The latter two, along with Kharia Thar and Mal Paharia, are closely related to Western Bengali dialects, but are typically classified as separate languages.
There are many more minor dialects as well, including those spoken in the bordering districts of Purnea and Singhbhum and among the tribals of eastern Bangladesh like the Hajong and the Chakma.
Dobhashi was a highly Perso-Arabised dialect, that started developing during the Bengal Sultanate period.
Many eastern Bengali dialects share phonological features with Assamese, including the debuccalisation of স & শ [ʃ] to হ [h] or খ [x].
The influence of Tibeto-Burman languages on the phonology of eastern Bengali is seen through the lack of nasalised vowels, an alveolar articulation for the Retroflex stops ট [ʈ], ঠ [ʈʰ], ড [ɖ], and ঢ [ɖʱ], resembling the equivalent phonemes in languages such as Thai and Lao and the lack of distinction between র [ɹ] and ড়/ঢ় [ɽ].
Unlike most languages of the region, some Purbo Bengali dialects do not include the breathy voiced stops ঘ [ɡʱ], ঝ [dʑʱ], ঢ [ɖʱ], ধ [d̪ʱ], and ভ [bʱ].