How many weeks in 2027?
2027 has 52 ISO weeks. A year gets a 53rd week only when January 1 is a Thursday, or when a leap year starts on a Wednesday.
Week 1 runs Monday, January 4 – Sunday, January 10, 2027. The last week, week 52, runs Monday, December 27, 2027 – Sunday, January 2, 2028.
Counting US-style instead (Sunday-start weeks, week 1 contains January 1), December 31, 2027, a Friday, falls in US week 53.