Week Number
Convert between ISO week and date
Friday, March 27, 2026
8:06:12PM
Current Week of the Year
13
March 23, 2026 - March 29, 2026
Weeks left in this year: 40
ISO 8601 Calendar
March 2026
#
Sun
Mon
Tue
Wed
Thu
Fri
Sat
9
23
24
25
26
27
28
1
10
2
3
4
5
6
7
8
11
9
10
11
12
13
14
15
12
16
17
18
19
20
21
22
13
23
24
25
26
27
28
29
14
30
31
1
2
3
4
5
March 23, 2026 - March 29, 2026
Week Number: 13
Global Week Number & Planning Utility
Educational Insights
What is ISO-8601 Week Numbering?
While most people think of years in months, the global logistics and financial industries think in weeks. Standard ISO-8601 ensures that everyone from New York to Singapore is on 'Week 42' at the same time. This prevents massive errors in supply chain and project management.
Related Tools
Technical Insights
ISO-8601 week calculations determine week 1 as the week containing the year’s first Thursday.
Algorithms avoid locale quirks by operating on UTC-based anchor dates before mapping to local display.
Browse UI components are optimized to reduce re-renders when switching years and months.
Frequently Asked Questions
What is the ISO definition of week 1?
Week 1 is the week with the year’s first Thursday, ensuring consistent ISO-8601 numbering.
Can I convert a week number to dates?
Yes. Use the calculator to get start and end dates for any year/week.
How many weeks are in a year?
Most years have 52 weeks; some have 53 depending on how the weeks fall.
Is the calendar view interactive?
Yes. Browse months and see week numbers highlighted for quick reference.
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