Dates work differently from numbers when added together in Excel. For example, if you add January 1, 2015, and January 2, 2015, it does not come to February 3, 4030.
The reason is that each date is stored in Excel as a serial number. When adding the two dates together, actually the two serial numbers will add together.
For example, The serial number of "January 1, 2015" is 42,005, and the serial number of "January 2, 2015" is 42,006. When adding the two dates together, the serial number becomes 84,011, which is equal to "January 4, 2130" after converting in a date.
Example: In the following dataset, the start date is in column A, and the end date is in column B.
Formula: To get the new date after adding "February 1, 2015" (A3) and "June 1, 2015" (B3).
=TEXT(A3+B3,"MMM DD, YYYY")
The serial number for "February 1, 2015" is 42,036, and the serial number for "June 1, 2015" is 42,156. The sum of the two serial numbers is 84,192, which is "Jul 04, 2030" in the date format.
The above formula will return the short month names, please use the following formula if you want to convert the full month names.
=TEXT(A3+B3,"MMMM DD, YYYY")
The result will return the date of "July 04, 2030".