Dates work differently from numbers when adding together. For example, if you add January 1, 2015 to January 2, 2015, it does not come February 3, 4030.
The reason is that each date stores in Excel as a serial number. When adding the two dates together, actually the two serial numbers will add together.
For example, January 1, 2015 is 42,005 and January 2, 2015 is 42,006. When adding the two dates together, the serial number is 84,011, which is January 4, 2130 when converting in a date.
Please use the formula below to add the two dates together when there is a need.
=TEXT(A2+B2,"MMM DD, YYYY")
To have the full month names, you need to change from "MMM" to "MMMM", or use the formula below:
=TEXT(A2+B2,"MMMM DD, YYYY")