![]() This is because a year is 52 weeks and one day (or two days for leap years). In most ISO 8601 years, there are 52 weeks. The ISO week date 2014-W01-2 is part of calendar year 2013. Parsing an ISO year/week/day combination displays the same issues: format("Y-m-d"), "\n" To show the ISO 8601 year, you need to use the o specifier. The Y format specifier gives the calendar year which is not the same as the ISO 8601 year. ![]() If you do the following in PHP, you get an unexpected answer: format('Y-\WW-N'), "\n" The ISO year starts with (ISO) week 1, day 1, which is always a Monday. As you see with December 31st, the ISO 8601 year ( 2014) is not the same as the calendar year ( 2013). Examples are: 2013-W39-2 for today and 2013-W40 for next Monday. It is also possible to omit the day-of-week ( yyyy "W" ww) to represent the start of the week (Monday) and to add - in the format (such as in yyyy "-W" ww "-" d. PHP supports the formats yyyy "W" wwĭ where yyyy is the ISO 8601 year, "W" a delimiter, ww the week number and d the day of the week (with 1 being Monday, and 7 being Sunday). With the year number (2012, 2013, etc), the week number (01-53) and the day number (1-7) you can describe a day. Week number 1 of each year is the first week in a year that has the first Thursday of the year, or in other words, the week containing January 4th. Each year has 52 or 53 weeks and weeks always start on a Monday. Week numbers are defined in this same ISO 8601 standard. In the past few weeks I've seen a few bug reports in the PHP bug system ( 6560) that deal with another aspect of this same calendar: week numbers. Number of the week in the year that occurs, based on a week beginning on Monday (the second argument, 2).Back in 2009 I wrote that PHP calendar implementation uses the ISO 8601 calendar for year numbers. Number of the week in the year that occurs, based on weeks beginning on Sunday (default). If you need to, you can adjust the column widths to see all the data. For formulas to show results, select them, press F2, and then press Enter. If Return_type is out of the range specified in the table above, a #NUM! error is returned.Ĭopy the example data in the following table, and paste it in cell A1 of a new Excel worksheet. If Serial_number is out of range for the current date base value, a #NUM! error is returned. Januis serial number 39448 because it is 39,448 days after January 1, 1900. ![]() The default is 1.Įxcel stores dates as sequential serial numbers so they can be used in calculations. A number that determines on which day the week begins. Problems can occur if dates are entered as text. Dates should be entered by using the DATE function, or as results of other formulas or functions. The WEEKNUM function syntax has the following arguments: This system is the methodology specified in ISO 8601, which is commonly known as the European week numbering system. System 2 The week containing the first Thursday of the year is the first week of the year, and is numbered as week 1. System 1 The week containing January 1 is the first week of the year, and is numbered week 1. There are two systems used for this function: ![]() For example, the week containing January 1 is the first week of the year, and is numbered week 1. Returns the week number of a specific date. This article describes the formula syntax and usage of the WEEKNUM function
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