This app allows you to obtain the distance between two dates, using the Gregorian calendar as a pattern.
Keep in mind that this calendar was adopted by several countries at the end of 1582, to progressively adopt it by all until 1926 (this implies that with dates prior to 1926 the distances will be relative).
Please note that the location and time zone used makes the distance relative.
This app also allows you to obtain, given a date, the next commemoration regarding the current date (countdown or additive) and the distance to it.