MMddyy

MMDDYY is a date notation in which the month and day are represented by two-digit numbers, followed by a two-digit year. The format is commonly written with separators such as slashes or hyphens (for example, MM/DD/YY or MM-DD-YY) and is closely associated with informal US records and legacy data systems.

In everyday use, MMDDYY might appear as 07/04/23 for July 4, 2023. Because the year is only two digits, the century is ambiguous; dates such as 12/31/89 could refer to 1989 or 2089 in some contexts, and data shared across borders or decades may require additional context to resolve the century.

The format originated with practical constraints of earlier data entry and storage, where two-digit years saved space and characters. It remained widespread in forms, receipts, and certain software environments. The approach became a focal point during discussions of the Y2K problem, which highlighted the risks of interpreting two-digit years without explicit century information.

Modern practice generally favors more explicit standards to avoid ambiguity. ISO 8601, which uses the YYYY-MM-DD format, is recommended for international data exchange and new systems. In many US applications, MMDDYY persists in casual use, documentation, or legacy systems. When MMDDYY is necessary, adding the four-digit year or using month names can reduce confusion, and storing dates in standardized numeric or ISO formats is preferred to ensure consistent interpretation across users and software.