How We Calculate Every Date

Bangladesh uses the Bangla Academy calendar in the form the government revised in 2019. That revision fixes Pohela Boishakh on 14 April, so the Bengali year is the Gregorian year minus 593 from 14 April onward and minus 594 before it. 21 February 2026 is 8 Falgun 1432; 14 April 2026 is 1 Boishakh 1433.

Month lengths never vary except for one: Boishakh to Ashwin have 31 days each, Kartik, Ogrohayon, Poush and Magh have 30, Falgun has 29 and Chaitra has 30. Falgun gains a 30th day whenever it contains 29 February. That is how the Gregorian leap day is absorbed without moving the new year, and it is why the national days keep the same Bengali date every year: 21 February is always 8 Falgun, 26 March is 12 Chaitra, 15 August is 31 Srabon and 16 December is 1 Poush.

Two consequences catch people out. The first is that this is not the calendar used in West Bengal. The traditional panjika there ties each month to the sun's entry into a rashi, so month starts drift by a day and Pohela Boishakh usually falls on 15 April. The second is that the reformed rules only apply from 1394 Bangabda, which began in 1987. Older dates, on a land deed for instance, were written under the earlier astronomical calendar. The converter still accepts them but shows a warning, because the true date can differ by one to three days.

In our Bengali calendar grids the week begins on Friday, matching the layout of printed Bangladeshi panjikas. The English calendar grid begins on Sunday.

The conversion code is covered by an automated test suite. It anchors 1 Boishakh to 14 April across leap years, checks the year switch on either side of 14 April, checks the start of every month, and converts every day in both directions to confirm nothing is lost. The suite runs before each deploy.

There is no single Hijri calendar. Saudi Arabia publishes the Umm al-Qura calendar, an arithmetic table used across the Gulf, and we take it as the starting point through the calendar support built into modern browsers and Node. Bangladesh, though, begins each month on its own moon sighting, decided by the Islamic Foundation's National Moon Sighting Committee after Maghrib on the 29th of the running month. That decision lands one day after Umm al-Qura in almost every month, so every Hijri date on the Bangladesh pages is shifted back by one day.

The shift is a prediction, not a promise. When the committee announces the start of a month we record the announced Gregorian date and count that month's days from it, so announced months are exact. Recent Ramadan, Shawwal, Dhul-Hijjah and Muharram starts are pinned this way. For the running month, until the 29th, the displayed date is our best estimate and can move by a day. Holiday lists mark such dates with an asterisk.

The India pages use the Umm al-Qura date without the one-day shift. The shift encodes the Bangladesh committee's pattern specifically, and applying it elsewhere would be a guess.

Prayer times are computed with the adhan library from each location's own latitude and longitude, not copied from a city timetable. For Bangladesh, India and Pakistan the method is that of the University of Islamic Sciences, Karachi, which places Fajr and Isha at a solar depression of 18 degrees, with Asr on the Hanafi rule: when an object's shadow is twice its own length. Saudi cities use the Umm al-Qura method with Shafi Asr.

A raw calculation does not match the Islamic Foundation's Dhaka timetable exactly. We compared the two day by day across the thirty days of Ramadan 1447 and found the calculation ran about four minutes early for Fajr and two minutes early for Maghrib, so those two offsets are added. The Foundation's own timetable remains the authority for sehri and iftar. Treat ours as a close working reference, and if the two differ, follow the Foundation.

Times are shown in each location's time zone, rounded to the minute. Above 48 degrees of latitude, where the sun may not sink 18 degrees below the horizon in summer, the calculation falls back to the high-latitude rule adhan recommends for that place.

Sunrise and sunset use the same solar geometry as the prayer-time engine, run for each of the 64 district headquarters at its own coordinates. Moon phase, illumination and the quarter moons come from astronomy-engine, a modern implementation of the standard astronomical algorithms. Eclipse pages take the global circumstances of each eclipse from the same engine and then judge visibility from Dhaka, which stands in for the whole country to within a few minutes.

Purnima, Amavasya and Ekadashi dates follow the traditional rule: the tithi running at sunrise in Dhaka is the tithi of the day. That is why a full moon that peaks late at night can be listed on the following calendar day.

The daily panchang is calculated for Dhaka with the panchangam-js library using the Lahiri ayanamsa, the sidereal reference adopted by the Indian Calendar Reform Committee and followed by Bangladeshi panjikas. Tithi, nakshatra, yoga and karana are listed with their exact end times, and the panchang day runs from one sunrise to the next. Lunar months are counted on the amanta system, ending on the new moon, which is the Bengal convention for festival dates.

Government holidays for the current and previous year are entered by hand from the gazette notification issued by the Cabinet Division. For years without a gazette yet, the list is generated from the same fixed-date rules, with Islamic dates from the Hijri method above and Hindu and Buddhist dates from the panchang, and it is replaced once the gazette for that year is published. Moon-dependent holidays such as the two Eids, Shab-e-Barat and Eid-e-Milad-un-Nabi show the gazetted date; the observed day can move by one after moon sighting.

Every "today" on the site is Bangladesh time, UTC+6, even when you open the page from abroad. The live clock shows Bangladesh and India time side by side. The date rolls over at midnight Dhaka time, and prayer times, panchang and moon data for the day are recomputed on each request rather than served from a cache.