Conversion

The two functions this library exists for: converting between Gregorian (AD) and Bikram Sambat (BS).

func ADToBS(t time.Time) (Date, error)

Converts a Gregorian calendar date to Bikram Sambat. Only the Year, Month and Day components of t are used — time-of-day and location are ignored. Returns an error wrapping ErrOutOfRange if t falls outside the Gregorian range corresponding to MinBSYear..MaxBSYear.

func BSToAD(d Date) (time.Time, error)

Converts a Bikram Sambat date to the corresponding Gregorian calendar date, returned as a time.Time at UTC midnight. Returns an error wrapping ErrInvalidYear, ErrInvalidMonth or ErrInvalidDay if d is not a real, supported Bikram Sambat date.

Example

ad := time.Date(2026, time.September, 22, 0, 0, 0, 0, time.UTC)
 
d, err := bs.ADToBS(ad)
// d == bs.Date{Year: 2083, Month: 6, Day: 6}, err == nil
 
back, err := bs.BSToAD(d)
// back == time.Date(2026, 9, 22, 0, 0, 0, 0, time.UTC), err == nil

Timezone behavior

ADToBS normalizes its input to a UTC-midnight calendar date before converting, so the same Gregorian calendar date always converts to the same BS date regardless of which timezone the time.Time is expressed in.

kathmandu, _ := time.LoadLocation("Asia/Kathmandu")
newYork, _ := time.LoadLocation("America/New_York")
 
t1 := time.Date(2026, 9, 22, 0, 0, 0, 0, kathmandu)
t2 := time.Date(2026, 9, 22, 23, 59, 59, 0, newYork)
 
d1, _ := bs.ADToBS(t1)
d2, _ := bs.ADToBS(t2)
// d1 == d2 == bs.Date{2083, 6, 6}

ⓘ

Every one of the 44,562 supported days round-trips exactly in both directions (BS → AD → BS and AD → BS → AD) — this is checked exhaustively in the library's test suite, not sampled.