Calendar Variants

The Bengali calendar system has evolved over time. bn-calendar provides native support for two calendar calculation rules: 'revised-2019' and 'revised-1966'.

Variant Overview

Variant	Description	Leap Year Rule	Default
`'revised-2019'`	Official Bangladesh national standard adopted in 2019 by Bangla Academy.	Gregorian leap year rules	Yes
`'revised-1966'`	Revised calendar established in 1966 by Dr. Muhammad Shahidullah committee.	`bnYear % 4 === 2`	No

Month Lengths Comparison

The two variants differ in how month lengths are distributed and how leap years adjust Falgun (month 11).

Revised 2019 Standard (`'revised-2019'`)

Months 1 to 6 (Boishakh to Ashwin): 31 days
Months 7 to 10 (Kartik to Magh): 30 days
Month 11 (Falgun): 29 days (30 days in leap year)
Month 12 (Choitro): 30 days

Month #	Month Name (Bangla)	Normal Year Days	Leap Year Days
1	বৈশাখ (Boishakh)	31	31
2	জ্যৈষ্ঠ (Joishtho)	31	31
3	আষাঢ় (Asharh)	31	31
4	শ্রাবণ (Srabon)	31	31
5	ভাদ্র (Bhadro)	31	31
6	আশ্বিন (Ashwin)	31	31
7	কার্তিক (Kartik)	30	30
8	অগ্রহায়ণ (Ogrohayon)	30	30
9	পৌষ (Poush)	30	30
10	মাঘ (Magh)	30	30
11	ফাল্গুন (Falgun)	29	30
12	চৈত্র (Choitro)	30	30

Revised 1966 Standard (`'revised-1966'`)

Months 1 to 5 (Boishakh to Bhadro): 31 days
Months 6 to 10 (Ashwin to Magh): 30 days
Month 11 (Falgun): 30 days (31 days in leap year)
Month 12 (Choitro): 30 days

Month #	Month Name (Bangla)	Normal Year Days	Leap Year Days
1	বৈশাখ (Boishakh)	31	31
2	জ্যৈষ্ঠ (Joishtho)	31	31
3	আষাঢ় (Asharh)	31	31
4	শ্রাবণ (Srabon)	31	31
5	ভাদ্র (Bhadro)	31	31
6	আশ্বিন (Ashwin)	30	30
7	কার্তিক (Kartik)	30	30
8	অগ্রহায়ণ (Ogrohayon)	30	30
9	পৌষ (Poush)	30	30
10	মাঘ (Magh)	30	30
11	ফাল্গুন (Falgun)	30	31
12	চৈত্র (Choitro)	30	30

Setting the Calendar Variant

You can specify the variant when instantiating BanglaCalendar using a configuration object:

typescript

import { BanglaCalendar
 } from 'bn-calendar';

// Using default 2019 variant
const defaultCal
 = new BanglaCalendar
();
console
.log
(defaultCal
.variant
); // 'revised-2019'

// Using 1966 variant
const legacyCal
 = new BanglaCalendar
({ variant
: 'revised-1966' });
console
.log
(legacyCal
.variant
); // 'revised-1966'

// Passing variant alongside date parameters
const specificCal
 = new BanglaCalendar
('১৪৩০', '১', '১', { variant
: 'revised-1966' });

Differences in Date Conversion

Due to month length and leap year differences, converting the same Gregorian date using different variants may yield slightly different Bangla date results (typically off by 1 day during specific months). Always select the variant that matches your domain requirements.

Calendar Variants ​

Variant Overview ​

Month Lengths Comparison ​

Revised 2019 Standard ('revised-2019') ​

Revised 1966 Standard ('revised-1966') ​

Setting the Calendar Variant ​