Problem:

Column B contains numbers of months which are to be added to the corresponding dates shown in column A.
We want to calculate the appropriate cumulative dates.

Solution 1:

Use the DATE, YEAR, MONTH, MIN, and DAY functions as shown in the following formula:
=DATE(YEAR(A2),MONTH(A2)+B2,MIN(DAY(A2),DAY(DATE(YEAR(A2),MONTH(A2)+B2+1,0))))

Solution 2:

Use the EDATE function as shown in the following formula:
=EDATE(A2,B2)