Useful for deadlines like "within 30 days of arrival" or "60 days before expiry".
Public holidays differ by country and year, so enter yours from the official calendar.
Calendar days simply move the date by N days. Business days skip the weekend you choose (Sat–Sun, Fri–Sat or Sunday only) and any public holidays you list; the tool does not know national holidays itself. The start date itself is day 0, so adding 30 days to 1 March gives 31 March.
Does it count the start date? No. The start date is day 0, so day 1 is the next day.
Are public holidays excluded from business days? Only the ones you list under Business-day options. Take the dates from the official holiday calendar of the country that set your deadline.
Which time zone is used? Dates are treated as plain calendar dates, so there is no time zone shift.
Informational tool, not legal or tax advice. Confirm requirements with the official authority. Everything runs in your browser; nothing is uploaded.