Different date formats in Excel

Question

I have a csv that contains a list of dates, once imported into Excel they are in 2 different formats. How can I get them all in the same format?

Example:

01/23/2012
01/26/2012
40910
41031

Solution

You probably have a BIG issue with your file!

Probably, Excel is recognizing dates as "dd/mm/yyyy" but your data is "mm/dd/yyyy" formatted.

So, your numbers are really dates (just format, as @t.thielemans suggested). But are incorrectly parsed - month and day are switched!

Solution (assuming your dates are on A:A column):

To convert text to date:

 =DATE(RIGHT(A1;4);LEFT(A1;2);MID(A1;4;2))

To correct day/month:

 =DATE(YEAR(A1);DAY(A1);MONTH(A1))

Detect whether cell has date (dates are numbers, in Excel) or text:

 =ISNUMBER(A1)

Finally, all combined within one formula:

 =IF(ISNUMBER(A1);DATE(YEAR(A1);DAY(A1);MONTH(A1));DATE(RIGHT(A1;4);LEFT(A1;2);MID(A1;4;2)))

Just drag last formula from first row to end of your data and then format it as you wish (see @t.thielemans solution).