Short answer: yymmdd = 2-digit year + 2-digit month + 2-digit day, six digits in total. March 5, 2026 is 260305. Because the year has only two digits, you cannot tell the century (19xx or 20xx), which is the main difference from yyyymmdd (8 digits).
What each letter means
| Symbol | Meaning | Digits | March 5, 2026 |
|---|---|---|---|
| yy | Last 2 digits of the year | 2 | 26 |
| mm | Month (01–12) | 2 | 03 |
| dd | Day (01–31) | 2 | 05 |
| yymmdd | 260305 |
y is for year, m for month, d for day. The number of letters is the number of digits. With a 4-digit year it becomes yyyymmdd; with only year and month it is "yymm" (March 2026 → 2603).
Examples
| Date | yymmdd | yyyymmdd |
|---|---|---|
| March 5, 2026 | 260305 | 20260305 |
| December 31, 2026 | 261231 | 20261231 |
| April 7, 1990 | 900407 | 19900407 |
| January 9, 2005 | 050109 | 20050109 |
Pad single-digit months and days with a leading zero (January 9 → 0109) and do not add separators. With slashes, "26/03/05" is called yy/mm/dd.
The pitfall: the century is unclear
"900407" can be read as April 7, 1990 or April 7, 2090. Systems resolve this with a cut-off rule:
- Excel (default settings): two-digit years 00–29 are treated as 2000–2029 and 30–99 as 1930–1999. This cut-off can change with the Windows settings.
- Programs and forms: some use their own base year. Check the specification.
For data that mixes dates from many decades, such as birth dates or contract dates, store the 8-digit yyyymmdd instead.
yymmdd compared with other formats
| Format | Example (March 5, 2026) | Notes |
|---|---|---|
| yyyymmdd | 20260305 | 8 digits, the century is clear. Works in file names and sorts by name = by date |
| yymmdd | 260305 | Short, but the century is ambiguous and it is easy to confuse with other 6-digit numbers |
| yy/mm/dd | 26/03/05 | Readable, but the slash cannot be used in Windows file names |
| mmddyy | 030526 | US order. Read differently in other countries |
| ddmmyy | 050326 | Common in Europe. Watch the day/month order |
For how the order differs by country, see Is 08/09 August 9 or September 8?
Convert in Excel
- Change only the display: right-click the cell → Format Cells → Custom → type
yymmdd - Convert to text:
=TEXT(A1,"yymmdd") - Turn 260305 back into a date (2000s):
=DATE(2000+LEFT(A1,2),MID(A1,3,2),RIGHT(A1,2)). If your data includes the 1900s, replace 2000 accordingly.
Using yymmdd in file names
A name like "260305_minutes.xlsx" sorts by date within the same century, just like yyyymmdd. For long-term records, the 4-digit year of yyyymmdd is safer. See Date at the start or end of a file name? and Standardizing file name dates in yyyyMMdd.
Type it with one key
Typing six or eight digits by hand invites slips like "260350". InsertDate is a Windows app that types today's date in your chosen format when you press the Insert key. See the supported formats on the download section.
Frequently Asked Questions
What is yymmdd?
It is a 6-digit date format: the last two digits of the year, two digits for the month and two for the day, without separators. March 5, 2026 is 260305.
What is the difference between yymmdd and yyyymmdd?
The year has 2 digits in yymmdd and 4 in yyyymmdd. yyyymmdd (8 digits) shows the century; yymmdd (6 digits) is shorter but ambiguous between the 1900s and 2000s.
Are yy/mm/dd and yymmdd the same?
The order is the same, but yy/mm/dd uses slashes. A slash cannot be used in Windows file names, so file names use the separator-free yymmdd.
What is yymm?
A 4-digit year-and-month format: the last two digits of the year followed by the month. March 2026 is 2603.
Try InsertDate Free for 7 Days
Press Insert. Get today's date in yyyyMMdd. Works in almost any Windows app, including Excel, Word and Notepad, with no configuration. To type into an app running as administrator, run InsertDate as administrator too.
InsertDate is a Windows 10/11 app. Reading on a phone? Open this page on your PC to install it.