These are the next holy days for December.
I used the site http://www.iskcongbc.org/vcal/. Please, let me know if something is incorrect or missing.
11th (Su) – Ekadasi, Fast for Moksada Ekadasi, advent of Srimad Bhagavad-gita;
12th (Mn) – Dvadasi, fast break for Moksada Ekadasi 7:15-8:18;
15th (Th) – Purnima, end of Katyayani vrata, beginning of Narayana Masa;
19th (Mn) – Caturthi, disappearance of Srila Bhaktisiddhanta Sarasvati Thakura (fast till noon);
26th (Mn) – Ekadasi, fast for Saphala Ekadasi, disappearance of Devananda Pandita;
27th – (Tu) – Dvadasi, fast break for Saphala Ekadasi 8:53 – 10:35;
28th – (We) – Trayodasi, disappearance of Sri Mahesa Pandita and Sri Uddharana Datta Thakura;
31st – (Sa) – Pratipat, appearance of Sri Locana dasa Thakura
Y.s.
Ramapriya