Use the EDATE function: `=EDATE(A1,3)`
Replace `A1` with the cell containing the date
Replace `3` with the number of months to add
Use a negative number to subtract months: `=EDATE(A1,-3)`
Format the result cell as a date if needed
Use the DATE function for a formula-based alternative: `=DATE(YEAR(A1),MONTH(A1)+3,DAY(A1))`
Use `EOMONTH` to add months and return the month-end date: `=EOMONTH(A1,3)`