How many days, weeks and working days lie between two dates.
It depends on the question, and this is where the common mistake lives. The difference between 1 and 10 March is nine days, but the number of days from 1 to 10 March inclusive is ten. Leave and deadline calculations usually want the second.
Count whole months from the start date first, then the leftover days separately. From 15 January to 20 March is two months and five days. Treating months as fixed thirty-day blocks is wrong, because their lengths differ.
If the span includes 29 February it adds a day. A leap year is any year divisible by four, except century years not divisible by four hundred. So 2000 was a leap year and 1900 was not, and the calculator handles this for you.
Subtract Saturdays and Sundays from the total, then any public holidays that fall on a weekday. In Latvia the number of holidays varies year to year, since some move with the day of the week, so check the calendar for the specific year.