The International Week Calendar (IWC) is a subset of the International Calendar (IC), hence a standardized variant of the proleptic Gregorian calendar (PGC), more specifically ISO week date. The International Standard Week Calendar (ISWC) is a limited specialization of the IWC. It runs in parallel with the International Month Calendar (IMC). International Week Calendar The week year has exactly 52 weeks (364 days) in a short year or 53 weeks (371 days) in a long year.