In the Islamic calendar, the new year is the 1st of the month of Muharam (January of the Islamic calendar) and, because the Islamic calendar includes 12 lunar months and 354 days, the number of days in the Islamic calendar differs from that in the Gregorian calendar by 11.
イスラム暦では、ムハッラム月（イスラム暦1月）1日が正月、イスラム暦は12太陰月、354日なので、グレゴリオ暦と11日違う。