What is Nepali Date? (Origination & Calendar)

The Nepali Date is based on the Bikram Sambat (Devanagari: विक्रम संवत्, abbreviated as BS or B.S.), the official national civil calendar of Nepal.

Used across all organs of the Nepalese state—from parliamentary legislation and Supreme Court decrees to banking operations, taxation, school academic sessions, and day-to-day citizen records—Bikram Sambat is a sophisticated solar sidereal calendar with roots extending over two millennia.

Historical Genesis of Bikram SambatCopy Anchor Link

The Founding in 57 BCECopy Anchor Link

Bikram Sambat originated in 57 BCE (Before Common Era) in the ancient city of Ujjain (in modern Madhya Pradesh, India). According to widespread historical tradition, the era was instituted by King Vikramaditya of Ujjain to commemorate his decisive military victory over the invading Saka (Indo-Scythian) forces, liberating the region and relieving the financial debt of his citizens.

Because the era was inaugurated in 57 BCE, Bikram Sambat is approximately 56.7 years ahead of the Western Gregorian calendar (Common Era / AD).

Evolution of the Era's Inscriptional NameCopy Anchor Link

Epigraphic and numismatic records show that the name of this calendar era evolved across three distinct phases:

1. Krita Era (कृत संवत्): Earliest stone inscriptions from the 3rd to 5th centuries CE referred to this system as Krita, possibly honoring a foundational event or sovereign leader.
2. Malava Era (मालव संवत्): Between the 5th and 9th centuries CE, the era was called Malava Gana Sambat (the era of the Malava republic), corresponding to the migration and governance of the Malava tribe.
3. Vikrama Samvat (विक्रम संवत्): By the 9th and 10th centuries CE, starting prominently around the Dholpur stone inscription (dated 842 CE / 898 BS), the era became permanently identified with King Vikramaditya.

The Calendar Eras of NepalCopy Anchor Link

Nepal has one of the world's richest epigraphic and calendar traditions, having utilized several prominent eras throughout its documented history:

1. Saka Sambat (शक संवत् - 78 CE)Copy Anchor Link

Introduced in ancient Nepal during the Licchavi period, the Saka Sambat was the primary calendar of early royal inscriptions. The oldest dated stone epigraph in Nepal—the pillar inscription of King Manadeva I at the Changu Narayan Temple—is dated 386 Saka Sambat (464 CE / 521 BS).

2. Manadeva Sambat / Amshuverma Era (576 CE)Copy Anchor Link

During the late Licchavi period under rulers such as King Amshuverma and King Jisnugupta, a shortened regional calendar system known as the Manadeva Sambat was employed across the Kathmandu Valley for public administration and religious foundations.

3. Nepal Sambat (नेपाल संवत् - 879 CE / 936 BS)Copy Anchor Link

Founded by Shankhadhar Sakhwa on Kartik Shukla Pratipada in 879 CE after he cleared the debts of all citizens in the Kathmandu Valley during the reign of King Raghavadeva. Nepal Sambat served as the principal civic, lunar, and commercial calendar of the Malla Dynasty (1200–1768 CE) and remains revered today as a national heritage calendar of Nepal.

4. Bikram Sambat in Ancient and Medieval NepalCopy Anchor Link

While Nepal Sambat predominated in the Kathmandu Valley's domestic trade, Bikram Sambat maintained continuous usage across western and northern Nepal:

• In the Khasa Malla Empire of the Karnali basin (centered in the Sinja Valley, Jumla), Bikram Sambat was the undisputed official calendar. The Dullu Stone Pillar of King Prithvi Malla (located in Dailekh) is engraved in Bikram Sambat 1414 BS (1357 CE) using the ancient Khas language.
• King Jayasthiti Malla (reigned 1382–1395 CE) and King Pratap Malla of Kathmandu utilized Bikram Sambat alongside Nepal Sambat in stone treaties, temple edicts, and Sanskrit panegyrics.

5. Unification and Official Adoption in Nepal (1768–1901 CE)Copy Anchor Link

When King Prithvi Narayan Shah of Gorkha unified Nepal and established Kathmandu as the capital in 1825 BS (1768 CE), he adopted Bikram Sambat as the standard calendar for royal seals (Lal Mohar), military directives, treaties, and administrative governance.

In 1958 BS (1901 CE), during the premiership of Rana Prime Minister Chandra Shumsher Jung Bahadur Rana, Bikram Sambat was formally promulgated by imperial decree as the sole official civil and administrative calendar of the Kingdom of Nepal, standardizing astronomical solar calculations across all government offices.

Chronological Timeline of EventsCopy Anchor Link

Explore the two-thousand-year progression of Bikram Sambat from its ancient foundation to its constitutional mandate in modern Nepal:

Astronomical Foundations & Calendar MechanicsCopy Anchor Link

Unlike the Western Gregorian calendar, which is a solar tropical calendar based on the cycle of the seasons (equinoxes and solstices), Bikram Sambat is a solar sidereal (Nirayana) calendar governed by the principles of classical Hindu astronomy (Surya Siddhanta).

1. The Sidereal Solar Year (Nirayana Saur Varsha)Copy Anchor Link

A sidereal year is the time it takes the Earth to complete one full revolution around the Sun relative to the fixed stars.

• The tropical year (used by Gregorian) equals approximately 365.2422 days.
• The sidereal year (used by Bikram Sambat) equals approximately 365.25636 days.
• Due to the precession of the equinoxes (Ayanamsha), the sidereal year advances forward relative to the tropical year by approximately 1 day every 71.6 years.

2. Solar Ingress (Sankranti)Copy Anchor Link

In Bikram Sambat, the first day of every month begins upon the Sun's transit (Sankranti) from one zodiac constellation (Rashi) into the next:

• Mesha Sankranti (Aries Ingress): Marks the entrance of the Sun into the constellation of Mesha (Aries). This exact astronomical occurrence defines Baisakh 1, celebrating Nepali New Year (Nawa Barsha).
• Makar Sankranti (Capricorn Ingress): Marks the Sun's entrance into Makara, signaling the winter solstice turning point and the festival of Maghe Sankranti.

3. Kepler's Second Law & Variable Month Lengths (29 to 32 Days)Copy Anchor Link

A defining characteristic of Bikram Sambat is that month lengths vary between 29 and 32 days from year to year.

This is not arbitrary; it is a direct consequence of celestial mechanics:

1. According to Kepler's Second Law, Earth travels faster along its elliptical orbit when it is closest to the Sun (perihelion, occurring in early January) and slower when it is farthest from the Sun (aphelion, occurring in early July).
2. Because the Earth moves faster during the northern hemisphere's winter, the Sun appears to traverse the winter constellations (Dhanu, Makara, Kumbha) in less time. Consequently, winter months like Kartik, Mangsir, Poush, and Magh typically span 29 to 30 days.
3. During the northern hemisphere's summer, the Earth moves slower in its orbit, taking longer to traverse constellations like Mithuna and Karkata. Consequently, summer months like Jestha, Ashadh, Shrawan, and Bhadra typically span 31 to 32 days.

[!NOTE] Because the exact moment of Sankranti can occur at any hour of the day or night, canonical Panchanga rules determine whether the new month begins on the same solar day (if Sankranti occurs before sunset or noon) or the following solar day. This produces variations where a given month may have 31 days in one year, but 32 days in another.

The 12 Nepali Months & Seasonal Cycles (Ritus)Copy Anchor Link

The Bikram Sambat year consists of 12 solar months categorized into six traditional two-month seasons (Ritus):

Days of the Week (Vaar)Copy Anchor Link

The seven-day week in Bikram Sambat mirrors the classical planetary order (Navagraha):

The Nepalese Fiscal Year (Aarthik Barsha)Copy Anchor Link

In Nepal, both public finance and commercial corporate reporting run on an official fiscal cycle defined entirely by Bikram Sambat dates:

• Fiscal Year Start: 1 Shrawan (approximately mid-July).
• Fiscal Year End: Last day of Ashadh (approximately mid-July of the following year).
• Format: Written as YYYY/YY in BS (for example, 2081/82 BS).
• Quarterly Accounting Windows:
  • Q1 (First Quarter): Shrawan 1 – Kartik end
  • Q2 (Second Quarter): Mangsir 1 – Poush end
  • Q3 (Third Quarter): Magh 1 – Chaitra end
  • Q4 (Fourth Quarter): Baisakh 1 – Ashadh end

All corporate income tax filings, government budget announcements (constitutionally mandated on 15 Jestha BS), and audited balance sheets operate strictly within this fiscal boundary.

Bikram Sambat (BS) vs. Gregorian (AD) ComparisonCopy Anchor Link

Technical Implications for Software EngineeringCopy Anchor Link

Building software applications that handle Bikram Sambat presents unique architectural requirements that do not exist with purely algorithmic calendars:

1. Mathematical Algorithms Cannot Predict Month LengthsCopy Anchor Link

In the Gregorian calendar, determining if a year is a leap year requires a simple formula:

(year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0)

In Bikram Sambat, no such modular formula exists. Because month lengths depend on the precise astronomical minute of the Sun's transit across constellations as observed from Kathmandu, month lengths are certified yearly by the Nepal Panchanga Nirnayak Samiti.

2. Comprehensive Calendar Mapping & Annual Ashwin VerificationCopy Anchor Link

Because modular formulas cannot predict month lengths, reliable date libraries must embed pre-computed lookup matrices containing verified month lengths for historical and modern Bikram Sambat years.

The Nepali Date Library embeds calendar mapping data spanning 1976 BS through 2100 BS (more than 124 years). Because the official Government of Nepal calendar for the upcoming year is released annually in the month of Ashwin (Ashoj) by the Nepal Panchanga Nirnayak Samiti, the library verifies dates up to the current active year and incorporates authoritative government updates annually upon publication.

3. Database Architecture RecommendationCopy Anchor Link

When architecting systems supporting Bikram Sambat:

• Storage Layer: Store all temporal values in databases as standard UTC timestamps or ISO-8601 Gregorian dates (YYYY-MM-DD).
• Application Layer: Use nepali-date-library to convert UTC timestamps to Bikram Sambat dates for UI display, fiscal reports, date pickers, and localized formatting.
• Form Inputs: Convert user-entered Bikram Sambat values to Gregorian prior to saving in persistent storage.

4. Nepal Standard Time (NPT)Copy Anchor Link

Nepal Standard Time is UTC+05:45, one of the few non-hourly timezones in the world. It is calculated based on the meridian passing through the summit of Mount Gauri Shankar at longitude 86°15' East. When performing date calculations near midnight, ensure that your application accounts for the +05:45 offset to avoid single-day boundary shifts.