Monthly calendar with week numbers — click any date to see details
The Gregorian calendar is the most widely used civil calendar in the world. It was introduced by Pope Gregory XIII in 1582 as a reform of the Julian calendar. The calendar has 12 months with a total of 365 days in a common year and 366 days in a leap year.
ISO week numbering (ISO 8601) defines that weeks start on Monday. Week 1 of the year is the week that contains the first Thursday of January, which also means it is the week containing January 4. This is the most common standard used internationally in business and commerce.