The little calculators I kept going back to the same sites for. Everything runs in this page. Nothing gets saved, and the page is locked down so it can't send what you type anywhere.
Click any answer to copy it.
Paste a link that's already tagged into Website URL and its tags move into the fields, so you can check or change them.
Weekdays skip Saturdays and Sundays, not holidays. Adding a month to the 31st lands on the last day of a shorter month.