Convert any date between the Gregorian (AD) calendar and the Nepali Bikram Sambat (BS / बिक्रम सम्बत) calendar, the official civil calendar of Nepal. The tool works in both directions and is accurate across the full supported range.
How it works
Bikram Sambat is a solar calendar whose month lengths range from 29 to 32 days and change from one year to the next. Because of this, a fixed year-offset would drift and cannot be used — the converter instead relies on the published per-year table of BS month lengths.
It anchors the two calendars at a known point — 1 Baisakh BS 2000 = 14 April 1943 — and uses the Julian Day Number (JDN) as a neutral day count:
- BS → AD: sum the days in all whole BS years, whole months and days before the target date, add to the anchor’s JDN, then convert that JDN to a Gregorian date.
- AD → BS: convert the Gregorian date to a JDN, subtract the anchor, then walk the table year by year and month by month, consuming days until the remainder lands on a BS date.
Supported range: BS 2000–2089 (≈ AD 1943–2033).
Worked example
Take 1 Baisakh 2080 BS. Walking the table from the anchor year 2000 up to 2080 and summing the month lengths, the converter lands on 14 April 2023 in the Gregorian calendar — confirming the roughly 56-to-57-year gap and the mid-April new year.
The twelve Bikram Sambat months
| BS month | Order | Typical length | Approximate Gregorian period |
|---|---|---|---|
| Baisakh | 1 | 30–31 days | Mid-April to mid-May |
| Jestha | 2 | 31–32 days | Mid-May to mid-June |
| Ashadh | 3 | 31–32 days | Mid-June to mid-July |
| Shrawan | 4 | 31–32 days | Mid-July to mid-August |
| Bhadra | 5 | 31–32 days | Mid-August to mid-September |
| Ashwin | 6 | 30–31 days | Mid-September to mid-October |
| Kartik | 7 | 29–30 days | Mid-October to mid-November |
| Mangsir | 8 | 29–30 days | Mid-November to mid-December |
| Poush | 9 | 29–30 days | Mid-December to mid-January |
| Magh | 10 | 29–30 days | Mid-January to mid-February |
| Falgun | 11 | 29–30 days | Mid-February to mid-March |
| Chaitra | 12 | 30–31 days | Mid-March to mid-April |
The month lengths in this table are typical but not fixed — the official Nepali calendar publishes the exact length for each month each year, and they vary. This is what makes the conversion non-trivial and requires the per-year table lookup.
Why Bikram Sambat cannot use a simple offset
The most intuitive approach would be to simply add 56 or 57 years to the Gregorian year. This works approximately for the year, but breaks down for the day because:
- BS months are not aligned with Gregorian months — BS months start in mid-April, mid-May, and so on, not on the first of each Gregorian month.
- Month lengths in BS vary year to year between 29 and 32 days, unlike the Gregorian calendar which has fixed month lengths (except February).
- The exact day offset within the year shifts continuously.
The Julian Day Number approach sidesteps these issues by converting everything to a single continuous day count, then mapping back through the per-year table.
Bikram Sambat vs Vikram Samvat: an important distinction
The name sounds similar and the eras share the same ancient origin, but Nepali Bikram Sambat and Indian Vikram Samvat are not the same calendar. The Nepali BS is a solar calendar — each month corresponds to a solar period, and the year starts when the sun enters Aries. The Indian Vikram Samvat used in many northern Indian states is largely lunisolar, following the moon for months but intercalating periodically to track the sun. The two diverge by weeks in day-to-day dates despite the shared 57-year offset from Gregorian, which is why converting between them requires knowing which system is being used.
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