How today's Nepali date is decided
Bikram Sambat is a solar calendar. Each month begins at sankranti, the moment the sun enters a new rashi, and that is what fixes how many days a month gets — anywhere from 29 to 32. The official yearly patro published in Nepal settles those lengths, and Katigate reads from the same tables rather than a formula. That is why the AD date for, say, Asoj 1 drifts by a day from one year to the next.