Number of days between two dates

First date: (previous) day month (in figures) year
Second date: (following) day month (in figures) year

Between the first and the second date days pass.

Add days to a certain date

Initial date: day month (in figures) year
Number of days to add
to the initial date:
Final date: day month (in figures) year

NOTA: You can also write dates before Christ, by using negative numbers, as the following examples:
1 b.C. = 0; 2 b.C. = -1; 44 b.C. = -43; etc. However, the result cannot be exact for periods before the Julian reform of 46 b.C.

I got the algorithm from the function to calculate the Julian number offered by Claus Tondering in his web site (par. 2.15.1).

Il calendario Il calendarioVersione italiana
Author: Eugenio Songia
Creation date: 5/5/2007.