What is the difference between ISO 8601 and US standards?

ISO 8601 starts weeks on Monday and defines the first week of the year as the one containing the first Thursday. The US standard typically starts on Sunday and considers the week containing January 1st as the first week.

Can I calculate week numbers for multiple dates at once?

Yes, simply enable the 'Multiple Dates' option and enter one date per line in the input box.

Does this tool support leap years?

Yes, the calculator automatically accounts for leap years when determining the week number and day of the year.

What output formats are available?

You can export your results as a simple list, a formatted table, a JSON array, or CSV format.

Can I customize the start day of the week?

Yes, you can override the standard settings by selecting a specific start day like Monday, Sunday, or Saturday in the advanced settings.

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Week Number Calculator

Calculate the week number of a date within a year. Supports different week number calculation standards (ISO 8601, US standard, etc.) for project management, time planning, and data analysis.

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Inputs

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7 options

ContentPaste or type the main input values.1

Date InputtextareaRequired

SettingsAdjust formats, ranges, numbers, and modes.4

Week StandardselectRequiredOutput FormatselectRequiredStart of Week (Advanced)selectOptionalFirst Week Contains (Advanced)selectOptional

TogglesEnable or disable optional behavior.2

Multiple DatescheckboxOptionalEnabled when checkedProcess multiple dates (one per line)Include Detailed Date InformationcheckboxOptionalEnabled when checkedInclude additional date details like quarter, day of year, leap year info

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Week Number Calculator

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1. Project Sprint Planning

2. Annual Sales Reporting

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