Year 10,000 problem

The Year 10,000 problem (also known as the Y10K problem or the deca-millennium bug) is the class of all potential time formatting and storage bugs that would emerge when the need to express years with five digits arises. The problem can have discernible effects today, but is also sometimes mentioned for humorous effect as in RFC 2550.

Historical and technological trends suggest that in the actual year 10,000, it is practically impossible that any of the data processing technology or software in use today will still be active. Furthermore, it is possible that the calendars in widespread use around AD 10,000 will be different. However, five-digit years are already a problem today for some forward-looking analysis programs, such as software that examines proposals for the long-term handling of nuclear waste.

This problem can be seen in the spreadsheet program Microsoft Excel through at least its Office 2013 release, which stores dates as the number of days since 31 December 1899 (day 1 is 1900-01-01); similarly, Microsoft Access stores dates as the number of days since 30 December 1899 (day 1 is 1899-12-31). In either application, a date value of 2958465 will be correctly formatted as "31 December 9999", but adding 1 to that to step over to the expected date of "1 January 10000" will cause a formatting error; in Excel, for example, it will be displayed in the cell as a series of # characters. Excel also cannot automatically convert date-formatted strings such as "12/12/2007" to dates if the year exceeds 9999; "12/12/9999" is automatically converted to a date when entered into a cell, but "12/12/10000" is not. The Long Now Foundation ran into this limitation of Excel during the design of the 10,000 year clock.

SAP NetWeaver handles date variables as strings of 8 characters (YYYYMMDD).

The open source OpenOffice.org Calc program is able to display dates beyond the year 9999 correctly with five digit years, but at least through version 2.4 falls victim to the Year 32,768 problem: "31 December 32,767" is the highest available date it can properly display. 32767, or 2¹⁵ − 1, is the highest positive number that can be represented using a 16-bit signed integer, adding one to this value causes it to overflow, and Calc interprets the year as a large negative number, "1 January −32,768".

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