|Don’t enter dates with full stops (eg 10.11.13) because Excel doesn’t store them as dates, meaning a lot of useful information is unavailable.
Instead, use a slash (eg 10/11/13) or hyphen (10-11-13) when you enter dates.
Excel then stores them properly, and can manipulate them, eg: matching of dates, difference between dates, conditional formatting, selection of ranges.
However, if you do have full stops, all is not lost.
Make sure all new dates use slashes or hyphens when you add them.
Existing values can be converted to valid dates, meaning the power will be unleashed!