Use DATEDIF to find the total years. Using this formula requires that dates be entered using the DATE formula. Switch to the formula bar.
Use DATEDIF again with ym to find months.
When both arguments are numbers the DAYS function will use Enddate-Startdate for calculating the number of days between both dates as shown below. At last enter the numbers of years months weeks or days that you want to add for the given date. For example between 1 Jan 2020 and 15 March 2020 there are 2 months and 15 days. In the example shown the formula in D5 is.