Describe the bug
The membership duration in the user's role membership section is one day too short (End date seems not to be included in the calculation)...
The End date of a membership is the last day of the membership, so it needs to be included.

Screenshots

A membership from 1.1. to 31.12. of the same year should be 1 full year (not 11 months, 30 days).
A membership from 1.1. to 31.1. of the same year should be 1 full month (all of January), not 30 days.
A membership from 1.1. to 1.1. is a one day membership, not 0 days
etc.