Hi
I created a form just to explain this find it attached hereCalculateExamples.xls (26 KB)
Focus on the area shown below
Your output should be something like this
And as indicated by @Xiphware FYI depending on how pedantic you wish to be, you might be interested in this thread (specifically discussing leap years…). But since you just want years and months here - that is, the precise number of days doesn’t matter - the impact of leap years will be nominal.
Regards
Stephane