bsad-converter

Bikram Sambat (BS) ↔ Gregorian (AD) date conversion and the Nepali calendar (पात्रो). Zero dependencies · offline · bilingual (English + Nepali) · works in the browser and Node · TypeScript types included.

The calendar data is the verified medic/bikram-sambat month-length table — a widely-used, verified source. Epoch: 1 Baishakh 1970 BS = 13 April 1913 AD. Range: 1970–2090 BS (≈ 1913–2034 AD).

Install

npm install @nepalpatro/bsad-converter

Usage

import { adToBs, bsToAd, today, monthCalendar, toNepaliDigits } from "@nepalpatro/bsad-converter";

// English → Nepali
const bs = adToBs("2026-06-25");          // or adToBs(new Date())
bs.formattedEn;   // "Ashadh 11, 2083 BS"
bs.formattedNe;   // "असार ११, २०८३ बि.सं."
bs.weekdayNe;     // "बिहीबार"
bs.events;        // [] (or [{ en, ne }] on a national day)

// Nepali → English
bsToAd(2083, 1, 1);                        // "2026-04-14"  (Nepali New Year)

// Today, in Nepal time (Asia/Kathmandu)
today().formattedNe;                       // "असार ११, २०८३ बि.सं."

// A month as a calendar grid
const m = monthCalendar(2083, 1);          // Baishakh 2083
m.days;                                     // 31
m.firstWeekday.index;                       // 2  (Tuesday; 0 = Sunday)
m.dayList[0];                               // { day:1, dayNe:"१", ad:"2026-04-14", weekday:2, …, events:[…] }

toNepaliDigits(2083);                       // "२०८३"

CommonJS works too:

const { adToBs } = require("@nepalpatro/bsad-converter");

API

| Export | Signature | Returns | |---|---|---| | adToBs | (input: Date \| string) => BsDate | BS date (bilingual, weekday, events) | | bsToAd | (year, month, day) => string | Gregorian "YYYY-MM-DD" | | bsToAdDate | (year, month, day) => Date | Gregorian Date (UTC midnight) | | today | () => BsDate | today in Nepal (Asia/Kathmandu) | | monthCalendar | (year, month) => CalMonth | one BS month grid | | yearCalendar | (year) => CalMonth[] | all 12 BS months | | toNepaliDigits | (value: string \| number) => string | Devanagari numerals | | consts | MIN_BS_YEAR, MAX_BS_YEAR, AD_MIN, AD_MAX, BS_MONTHS | range + raw table |

BsDate = { year, month, day, monthEn, monthNe, iso, formattedEn, formattedNe, weekdayEn, weekdayNe, events }. CalDay = { day, dayNe, ad, weekday /* 0=Sun..6=Sat */, weekdayEn, weekdayNe, events }. CalEvent = { en, ne }.

Out-of-range or invalid input throws DateConversionError:

import { adToBs, DateConversionError } from "@nepalpatro/bsad-converter";
try { adToBs("2099-01-01"); } catch (e) { /* e instanceof DateConversionError */ }

Events

events covers fixed national days only (New Year, Republic / Constitution / Democracy / Martyrs' Day, Prithvi Jayanti, Maghe Sankranti, + fixed AD days: Labour Day, Women's Day, Christmas). Movable lunar festivals (Dashain, Tihar, Holi, Buddha Jayanti …) are intentionally not included — they shift yearly and require the official Nepal Panchanga.

Date picker

Build a Nepali (BS) date selector on top of monthCalendar(). See examples/date-picker.html for a complete, runnable widget — BS calendar grid, today + Saturday holidays highlighted, an AD input that jumps to the month, and the selected date shown in both BS and AD.

import { monthCalendar, toNepaliDigits } from "@nepalpatro/bsad-converter";

const cal = monthCalendar(2083, 3);     // असार 2083
cal.firstWeekday.index;                  // leading blank cells before day 1 (0 = Sunday)
cal.dayList.forEach(d => {
  // d.dayNe = "१२", d.ad = "2026-06-26", d.weekday (6 = Saturday), d.events
  // → render one cell per day; on click, surface d.ad + the BS date
});

Notes

• Timezone: today() uses Asia/Kathmandu (UTC+5:45, no DST).
• Sovereign: pure local computation; contacts no network and needs no API key.
• A live HTTP API and a citizen calendar page exist at https://nepal.gov.np/calendar.

License

MIT licensed