What Week of the Year Is It?
The calculator above shows the current week number of the year at the top, along with today's date and how many weeks remain until the end of the year. Week numbers follow the ISO 8601 standard, so week 1 is the week containing the first Thursday of the year, and each week starts on Monday. A typical year has 52 weeks, while some years have 53 weeks.
How ISO Week Numbers Work
The ISO 8601 standard defines a consistent way to number the weeks of the year:
- Every week starts on Monday and ends on Sunday.
- Week 1 is the week that contains the first Thursday of the year (equivalently, the week containing January 4).
- Because of this rule, the first few days of January can belong to the last week of the previous year, and the last days of December can belong to week 1 of the next year.
- A year has either 52 weeks or 53 weeks, depending on which day of the week the year starts and whether it is a leap year.
This is why a date like January 1 might fall in week 52 or 53 of the previous ISO year rather than week 1.
Find the Week Number for Any Date
Use the date picker to look up the ISO week number for any date. The calculator shows the week number along with the Monday-to-Sunday range of that week, so you can see exactly which days the week covers. The lookup defaults to today, and you can jump back to today at any time with the Today button.
Why Week Numbers Matter
Week numbers are widely used to plan and coordinate work throughout the year:
- Business planning — teams reference "week 32" instead of a date range to align across departments.
- Payroll periods — weekly and bi-weekly pay cycles are tracked by week number.
- Project schedules — sprints, milestones, and delivery dates are often mapped to specific weeks.
- Manufacturing — production runs, shipments, and date codes frequently use the ISO week number.
