Calculate the ISO 8601 week number and week-based year for a date.
ISO weeks always start on Monday and belong to whichever year contains their Thursday. That is why 1 January can fall in week 52 or 53 of the previous week-based year. Financial and manufacturing reporting uses ISO weeks precisely because every week has exactly seven days, unlike calendar months.
ISO Week Date
The ISO week is the week containing the Thursday, which determines the week-based year
The ISO week is the week containing the Thursday, which determines the week-based year ISO weeks always start on Monday and belong to whichever year contains their Thursday. That is why 1 January can fall in week 52 or 53 of the previous week-based year.
Financial and manufacturing reporting uses ISO weeks precisely because every week has exactly seven days, unlike calendar months.
This calculator takes 3 inputs: Date year, Date month, Date day. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.