Calendar Week Calculator
Find the calendar week for a date or the date for a calendar week. Quick, free, no registration required for instant date calculations.
Determine the calendar week (CW) according to ISO 8601 for any date.
Calendar week
KW 28 / 2026
Day of the week
Wednesday
Week (Mon - Sun)
07/06/2026 - 07/12/2026
Day of the year
Day 189 of 365
Calendar weeks in July 2026
Note: These calculations are for informational purposes only and do not replace professional tax or financial advice. All information without guarantee.
FAQ
Frequently Asked Questions
How are calendar weeks (KW) numbered?
According to ISO 8601, calendar week 1 is the week containing the first Thursday of the year. Weeks start on Monday. A year can have 52 or 53 calendar weeks.
Why does the calendar week sometimes differ between countries?
Most European countries use the ISO standard (Monday start, first week contains Jan 4). The US often uses a Sunday-start week where week 1 contains January 1, which can differ by one week.
Are leap years and holidays taken into account?
Yes — the calculator automatically considers leap years, German public holidays and varying month lengths. For working-day calculations weekends are correctly excluded.
Guide
Quick Answer
The calendar week calculator determines the calendar week (CW) of a date or shows all calendar weeks of a year with start and end dates.
What is the Calendar Week Calculator?
The calendar week calculator determines the calendar week (CW) of a date or shows all calendar weeks of a year with start and end dates.
How does the Calendar Week Calculator work?
Enter a date. The calculator shows the corresponding calendar week per ISO 8601. Alternatively enter a CW to get the start and end dates of that week.
Key Data and Facts
ISO 8601: CW starts on Monday. CW 1 contains the first Thursday of the year. A year has 52 or 53 calendar weeks.
Step-by-Step Guide
How to use the calendar week calculator step by step: 1. Enter a date -- the calculator shows the corresponding calendar week (CW) according to ISO 8601. 2. Alternatively enter the CW and year -- the calculator shows the Monday and Sunday of that week. 3. Understand the ISO 8601 rules: the week begins on Monday. CW 1 is the week that contains the first Thursday of the year (or, put differently: the week with 4 January). 4. Special features at the turn of the year: 1 January can fall in CW 52 or 53 of the previous year. 28-31 December can fall in CW 1 of the following year. A year has 52 or 53 calendar weeks. 5. Common applications: scheduling in companies (meetings in CW 15), delivery dates (delivery in CW 20), holiday planning. Tip: in Germany and most European countries ISO 8601 applies. In the USA the week begins on Sunday.
Calculation Example
April 10, 2026 falls in week 15. Week 1 of 2026 begins on Monday, December 29, 2026, and ends on Sunday, January 4, 2027.
Sources · E-E-A-T
Official sources
Calculations are based on applicable German laws and official data:
Full methodology at Methodology.
Date & Time
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