When you enter a date in Excel, you can use slashes (/) or dashes (-) as separators. If you enter a four-digit year, Excel interprets it as a date. For example, 12/12/2015 is interpreted as December 12, 2015. 01/02/2016 is interpreted as January 2, 2016.

If you enter a two-digit year, Excel interprets it as a day of the month. For example, 12/12/15 is interpreted as December 12, 2015. 01/02/16 is interpreted as January 2, 2016.

You can also enter dates without separators. If you enter a four-digit number, Excel interprets it as a date. For example, 12122015 is interpreted as December 12, 2015. 01022016 is interpreted as January 2, 2016.

If you enter a two-digit number, Excel interprets it as a day of the month. For example, 121215 is interpreted as December 12, 2015. 010216 is interpreted as January 2, 2016.