Week Number Calculator

"What week is it?" is a question that comes up constantly in business, project planning and scheduling — sprints, fiscal reporting, production schedules and shared calendars are often organized by week number rather than date. This tool shows the current week number prominently and lets you look up the week number for any date, using the ISO 8601 standard that most of the world's business and software relies on.

ISO 8601 week numbering has specific rules that trip people up, so it's worth stating them plainly: weeks start on Monday (not Sunday), and week 1 is defined as the week containing the year's first Thursday — equivalently, the week containing January 4th. This means the first few days of January can sometimes fall in the last week of the previous year, and late December can fall in week 1 of the next year. This tool implements those rules correctly, where many quick calculators get the year-boundary cases wrong.

Alongside the week number, you get the useful surrounding context: the day of the year (day 200 of 365), the quarter (Q3), the weekday, and how many weeks the ISO year contains (52 or 53). Whether you're logging work against week numbers, planning a schedule, or just settling "which week are we in?", it's an instant, accurate answer.