How BS to AD conversion actually works (and why it can't be a simple formula)

Nepal runs its official life on the Bikram Sambat (BS) calendar: citizenship, passports, certificates, property papers and festivals all use it. The Gregorian calendar used worldwide is a fixed, math-driven system — 31/30/28 days. Bikram Sambat is panchanga-based: months alternate between 29 and 32 days, and the exact lengths change year to year. That's why no simple arithmetic formula can convert BS to AD.

How tools do it

Reliable converters use a per-year month-length table covering the years people actually need (BS 2000–2090 on Nepali Tools). The table records how many days each BS month had in that year; conversion then counts days between your date and a known anchor (BS 1 Baishakh = mid-April). That's also why cheap calculators that assume "30 days per BS month" drift several days off.

What to double-check for official use

For visa, citizenship or university applications the stakes matter: first, read the BS date from your certificate exactly as printed (watch for handwritten months like जेट versus जेठ). Then convert with a table-based tool. Finally, when a form needs a birth date in writing, keep consistency across your passport and certificate — an unexplained one-day difference can cause queries, so prefer the officially converted form if the institution provides one.