Sunday is considered as the last day of the week. Meaning there would be five days in the first week, this means the week of January 1st falls under week number 1 of calendar year 2020.Ģ021 however -> starts at Friday January 1st. Honestly I didn't even knew.Ģ020 -> starts at Wednesday January 1st. It says: "according to the international ISO8601 ( ), the first week of a year will be the week that has 4 or more days of that calendar year in it.". When you translate it to English using i.e. This Dutch Wikipedia article describes how the week number is being calculated: This helps other users find it more easily via well I have just learned something interesting. If you liked this reply, please give it a thumbs up! If this reply has answered your question or resolved your challenge, please consider marking it as a Solution. PS - If you want me to go into detail on any of the expressions, happy to do so. You can probably combine some of these depending on your comfort level with expressions, but here's a sketch:
![week number calendar 2015 week number calendar 2015](https://i.pinimg.com/originals/d9/6b/cf/d96bcf2cc9f6b1e5287f2131a49e5c77.png)
That will give you the traditional week-start of Sunday, so just add one more to get the Monday. By using dayofWeek(), we can find out how far from Monday we are, and make that a negative number which we then add to the actual date from the step above.
![week number calendar 2015 week number calendar 2015](https://images-eu.ssl-images-amazon.com/images/I/510nbX1PiEL._SX300_QL70_.jpg)
![week number calendar 2015 week number calendar 2015](https://image.shutterstock.com/image-vector/calendar-2015-600w-204005383.jpg)