The old Icelandic calendar is not in official use anymore, but some Icelandic holidays and annual feasts are still calculated from it. It has 12 months, of 30 days broken down into two groups of six often termed "winter months" and "summer months". The calendar is peculiar in that each month always start on the same day of week. This was achieved by having 4 epagomenal days to bring the number of days up to 364 and then adding a "sumarauki" week in the middle of summer of some years. This was eventually done so as to ensure that the "summer season" begins on the Thursday between 9 and 15 April in the Julian calendar