Calculate the week number for any date, see current week dates, and convert between dates and week numbers. Perfect for project planning and scheduling.
A week number represents the specific week of the year. In the ISO 8601 calendar, weeks start with Monday and end on Sunday, with approximately 52 weeks in a year. The first week (Week 1) contains the first Thursday of the year. Some years may have 53 weeks when January 1 falls on a Thursday (or Wednesday in leap years).
The current week number and date range are shown automatically when you visit the page
Select any date to find its corresponding week number in the year
Enter a week number and year to see the corresponding date range
This tool shows the current ISO 8601 week number, the date range that week covers, and how many weeks are left in the year. You can also convert any date to its week number, or a week number back to its date range.
Week numbers are part of everyday planning across Europe and in many industries: payroll and shift rotas, manufacturing and retail calendars, logistics, and project schedules are often organised by "week 32" rather than by month. ISO 8601 is the standard almost all of those systems follow.
Weeks start on Monday and end on SundayWeek 1 is the week that contains the first Thursday of JanuaryEquivalently, week 1 is the week containing 4 JanuaryA year has 52 or 53 ISO weeks; 53 occurs when the year starts on a Thursday (or a leap year starts on a Wednesday)1–3 January can belong to week 52 or 53 of the previous year; 29–31 December can belong to week 1 of the next yearA Thursday, so it falls in week 1 of 2026. The week runs Monday 29 December 2025 to Sunday 4 January 2026.
A Wednesday. It belongs to ISO week 1 of 2026, not week 53 of 2025 — a classic source of off-by-one errors in reports.
Monday 3 August to Sunday 9 August 2026. Enter a week number and year to get the exact dates.
2020 was a leap year that began on a Wednesday, so it contained 53 ISO weeks. Most years have 52.
The current ISO week number is shown at the top of the tool, along with the Monday-to-Sunday dates it covers and the number of weeks remaining this year.
Under ISO 8601, week 1 is the week containing the year's first Thursday, which is the same as the week containing 4 January. Weeks always start on Monday.
If 1 January falls on Friday, Saturday or Sunday, that week's Thursday is still in December, so those days belong to the last week of the previous year.
52 in most years, 53 when 1 January is a Thursday or when a leap year starts on a Wednesday. 2026 has 53 weeks.
Often not. The common US convention starts weeks on Sunday and makes the week containing 1 January week 1, which can differ from ISO by one.
It matches Excel's ISOWEEKNUM function and the week numbers shown by most European calendar apps. Some apps default to a non-ISO scheme you may need to switch.