Week numbers in Excel

Using this downloadable Excel spreadsheet with all week numbers guarantees you a good overview, which will save you time and effort in the future. Here you find solutions for the coming years:

Please note that there are multiple systems for week numbering; this is the ISO week date standard (ISO-8601). Other systems use weeks starting on Sunday (US) or Saturday (Islamic). All weeks start on Monday and end on Sunday. 

The ISO week date system is effectively a leap-week calendar system that is part of the ISO 8601 date and time standard issued by the International Organization for Standardization (ISO) since 1988 (last revised in 2004) and, before that, it was defined in ISO (R) 2015 since 1971. It is used (mainly) in government and business for fiscal years, as well as in timekeeping. This was previously known as "Industrial date coding". 

The system specifies a week year atop the Gregorian calendar by defining a notation for ordinal weeks of the year. An ISO week-numbering year (also informally called an ISO year) has 52 or 53 full weeks. That is 364 or 371 days instead of the usual 365 or 366 days. The extra week is sometimes referred to as a leap week, although ISO 8601 does not use this term.