I do not accurately know how to calculate months and days between two dates. I am not even sure what sort of assumptions that I should make.

If I have these dates:

StartDate EndDate

3/28/2017 3/1/2018

3/29/2017 3/1/2018

3/30/2017 3/1/2018

3/31/2017 3/1/2018

1/2/2019 9/25/2019

1/25/2019 4/6/2019

a formula like this: =DATEDIF(A2,B2,"m")&" months & "&B2-EDATE(A2,C2)&" days" yields this: 11 months & 1 days

a formula like this: =DATEDIF(A3,B3,"m")&" months & "&B3-EDATE(A3,C3)&" days" yields this: 11 months & 1 days

a formula like this: =DATEDIF(A4,B4,"m")&" months & "&B4-EDATE(A4,C4)&" days" yields this: 11 months & 1 days

a formula like this: =DATEDIF(A5,B5,"m")&" months & "&B5-EDATE(A5,C5)&" days" yields this: 11 months & 1 days

a formula like this: =DATEDIF(A2,B2,"m")&" months & "&ABS(DATEDIF(A2,B2,"md"))&" days" yields this: 11 months & 1 days

a formula like this: =DATEDIF(A3,B3,"m")&" months & "&ABS(DATEDIF(A3,B3,"md"))&" days" yields this: 11 months & 0 days

a formula like this: =DATEDIF(A4,B4,"m")&" months & "&ABS(DATEDIF(A4,B4,"md"))&" days" yields this: 11 months & 1 days

a formula like this: =DATEDIF(A5,B5,"m")&" months & "&ABS(DATEDIF(A5,B5,"md"))&" days" yields this: 11 months & 2 days

a formula like this: =DATEDIF(A2,B2,"m")&" months & "&DATEDIF(A2,B2,"md")&" days" yields this: 11 months & 1 days

a formula like this: =DATEDIF(A3,B3,"m")&" months & "&DATEDIF(A3,B3,"md")&" days" yields this: 11 months & 0 days

a formula like this: =DATEDIF(A4,B4,"m")&" months & "&DATEDIF(A4,B4,"md")&" days" yields this: 11 months & -1 days

a formula like this: =DATEDIF(A5,B5,"m")&" months & "&DATEDIF(A5,B5,"md")&" days" yields this: 11 months & -2 days

What sort of formulas do people use in this situation and what are the assumptions? Any ideas?