Hebcal's hdate package converts between Hebrew and Gregorian dates.
It also includes functions for calculating personal anniversaries (Yahrzeit, Birthday) according to the Hebrew calendar.
Internally, it uses R.D. (Rata Die) day numbers.
Example
package main
import (
"fmt"
"time"
"github.com/hebcal/hdate"
)
func main() {
hd := hdate.New(5765, hdate.Adar2, 22)
year, month, day := hd.Greg()
fmt.Println(year, month, day)
// Output: 2005 April 2
hd2 := hdate.FromGregorian(2008, time.November, 13)
fmt.Println(hd2)
// Output: 15 Cheshvan 5769
}