The "Date" function would work for your purposes. It's in the format of =Date("y","m","d").
Depending on what you need it for, and how dynamic you want it to be, you can use references to another cell that contains the original date, and references to cells that contain the changes to be made. I use a version of this to find the first day of the month following 30 days from an employee's start date (including the start date, which is why I use 29 in the formula). The date is saved in column A, so after headers, the first date is in A2. My formula is =Date(Year(A2+29),Month(A2+29)+1,1). In the event that the month rolls from December to January because of the "+1" in the month section, the year is automatically rolled up to the next year. Simply format the cells for "Date", and it comes out fine.
Examples:
for start date 1/30/2017, formula returns 3/1/2017
for start date 1/31/2017, formula returns 4/1/2017
for start date 11/28/2017, formula returns 1/1/2018
At it's most dynamic, you could put your original date in A1, Years to Add/Subtract in A2, Months to Add/Subtract in A3, and Days to Add/Subtract in A4, with the following formula in A5: =Date(Year(A1)+A2,Month(A1)+A3,Day(A1)+A4). Positive numbers will add, negative numbers will subtract.