Master every deadline.

What these calculators are for

Date math looks trivial until weekends, public holidays, inclusive-versus-exclusive counting and country-specific rules collide. Most date disputes are not arithmetic errors; they are disagreements about a convention nobody wrote down. Does a ten-day notice period mean calendar days or business days? Does the clock start on the day of the event or the day after? If the deadline lands on a Sunday, does it roll forward, and whose public holidays count? Each of the 110 calculators here takes one such question, makes those choices visible as inputs instead of guessing, and shows the weekends, holidays and conventions behind the answer.

Where a period is fixed by statute, the calculator applies it and cites the primary source on its own page: the regulation, the statute or the agency that administers it, not a summary. Where the rule depends on your contract, jurisdiction or payroll calendar, it is an input. Public holidays are computed from each country's observance rules rather than stored as a list that goes stale. The site is written and maintained by Paul Clark of Redmoon Software, the methodology page sets out how the data and the logic are checked and corrected, and every calculation runs in your browser, so the dates you enter never leave the page.