Week number calculator

Week numbers are a common way of dividing a year into equal parts and tracking the passage of time. A week number is a number that represents the week of the year in which a particular date falls. For example, the first week of the year would be represented by week number 1, the second week would be week number 2, and so on.

There are several different methods for computing week numbers for a given date. One common method is to use the ISO-8601 standard, which defines a week as starting on a Monday and ending on a Sunday. Under this method, the first week of the year is the week that contains the first Thursday of the year. This means that the first week of the year can start on either the first or the second day of the year, depending on when the first Thursday falls.

To compute the week number for a given date using the ISO-8601 method, you can follow these steps:

1. Determine the day of the week on which the given date falls.
2. If the given date falls on a Monday, Tuesday, Wednesday, or Thursday, the week number is the number of whole weeks that have passed since the start of the year, plus one.
3. If the given date falls on a Friday, Saturday, or Sunday, the week number is the number of whole weeks that have passed since the start of the year.

To compute the date for a given week number, you can use the same steps, but in reverse. First, determine the day of the week on which the first day of the year falls. Then, add the number of whole weeks indicated by the week number to the first day of the year, and add one if the given week number is greater than or equal to the week number of the first Thursday of the year. This will give you the date for the first day of the given week number.