In Europe and most of the world, a week starts on Monday and ends on Sunday. The ISO 8601 standard defines week 1 as the week containing the first Thursday of the year — so it always has at least 4 days in the new year.
In the United States, Canada, Mexico, and Australia, the week starts on Sunday. Week 1 always begins on January 1st regardless of which weekday it falls on — this can result in up to 54 weeks in a calendar year.
The official notation is YYYY-Www-D — for example today is . The "W" prefix stands for "Week" and D is the day number (1=Mon).
Calculate the exact number of days, weeks, months, and working days between any two dates.
Find the date that falls a given number of days, weeks, or months before or after a starting date.