In a formula column, the MONTH_DELTA() function allows you to subtract two date columns to display the result in months:

MONTH_DELTA = time1 - time2

Formula

MONTH_DELTA(moment1, moment2)

Example

MONTH_DELTA(Début, Fin)

Configurator

Result

For the 2nd project, there is a 2 month difference between the End and Start columns.