Business Day Math Is Harder Than You Think

Quick: how many business days are in March 2026? If you answered 22, you skipped weekends but forgot that different countries have different holidays in March. The US doesn't have a federal holiday in March, so 22 is correct there. But India celebrates Holi. Mexico has Benito Juárez's birthday. Japan has Vernal Equinox Day. The correct answer depends entirely on where your users are. And that's just the beginning of why business day calculations are more complex than they appear. The Weekend Problem "Weekdays are Monday through Friday" is a reasonable assumption if your entire user base is in the Western world. It's wrong for about two billion people. In many Middle Eastern countries, the traditional work week runs Sunday through Thursday. Friday and Saturday are the weekend. In some countries, the weekend is Friday and Saturday. Others use Saturday and Sunday. A few have only a single-day weekend. Saudi Arabia, the UAE, and several other Gulf states recently shifted to a Saturday-Sund