Pick two dates to see the gap in days, weeks, months and years, with a separate business-day count that skips weekends. The second mode goes the other way: give it a date and a number of days to add or subtract and it tells you where you land.
The plain difference between 1 March and 3 March is two days - that is the number of nights, and the one you want for hotel bookings, interest accrual and most contracts. The inclusive count of three is the number of calendar days touched, which is what you want for "how many days is the conference". Both are shown because using the wrong one is a classic off-by-one.
Only Saturdays and Sundays are excluded. Public holidays differ by country, region and sometimes industry, so subtract yours separately. The same caveat applies to adding business days: a "ten working days" deadline calculated here will be optimistic across Christmas or a national holiday week.
The plain difference is exclusive: 1 March to 3 March is 2 days. An inclusive count, which is what you usually want for booking nights or project durations, is shown alongside it as 3 days.
No, only Saturdays and Sundays. Public holidays vary by country and region, so subtract those yourself for your jurisdiction.
Steuervergleich Kanton Zürich — Gemeindesteuern vergleichen (Deutsch)