ISO Week Date Converter

Convert calendar dates to ISO 8601 week dates, convert ISO week number to date, check ISO week-year edge cases, and batch-convert week dates with custom controls.

100% Browser-Based•Local Processing

ISO Week Bridge

Convert dates and ISO week codes

Use custom controls to convert a calendar date into YYYY-Www-D or convert ISO week-year, week, and weekday back into a calendar date.

ISO Result

ISO week date--Choose a date or ISO week to convert.
Calendar date--
Week range--
ISO week-year--
Weekday--
Weeks in year--
Boundary note--
No ISO week result yet.
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Privacy Focused

🔒 Local Processing. Your data never leaves your device.

Instant Results

🌐 Fully Client-Side. Runs instantly in your browser.

No Signup

⚡ No accounts. No hassle. Just open and use.

Browser Based

🚀 Works right in your browser. No installs, no downloads.

Overview

Convert ISO Week Dates Without Calendar Guesswork

ISO week dates are used in international scheduling, logistics, manufacturing, payroll, sprint planning, fiscal reporting, and software systems that need week-based dates instead of month-based dates. The format uses an ISO week-year, week number, and weekday, written like YYYY-Www-D.

Direct answer: Use this ISO Week Date Converter to convert a calendar date into an ISO 8601 week date such as 2026-W23-2, or convert an ISO week number and weekday back into the matching Gregorian calendar date.

This page targets searches such as ISO week date converter, ISO week number to date, date to ISO week date, convert week number to date, YYYY-Www-D converter, ISO week-year calculator, and 53 week ISO year. For plain week numbers, use the Week Number Calculator.

ISO Week Date Converter with custom calendar, ISO year and week steppers, weekday chips, ISO week range strip, copy summary, and batch ISO week conversion panel
The ISO Week Date Converter turns calendar dates into ISO 8601 week dates and converts ISO week numbers back into calendar dates with custom controls.
Features

ISO Week Conversion Features

Two-way conversionConvert Gregorian calendar dates to ISO week dates and ISO week numbers back to dates.
Custom date pickerUse a branded calendar overlay instead of a native browser date picker.
ISO week steppersAdjust ISO week-year and week number with custom controls that clamp 52 and 53 week years.
Weekday chipsPick ISO weekdays from Monday 1 through Sunday 7 with accessible custom buttons.
Week range stripSee the Monday-to-Sunday week range and switch days visually.
Batch converterPaste YYYY-MM-DD dates or YYYY-Www-D strings and convert multiple lines in one compact panel.
Use Cases

ISO Week Date Keywords Covered by Real Examples

These examples cover the exact long-tail searches people use when ISO week-year rules are confusing.

ISO week date converterConvert between Gregorian dates and ISO 8601 week dates.
ISO week number to dateEnter ISO year, week, and weekday to find the calendar date.
date to ISO week datePick or type a date and get the YYYY-Www-D value.
convert week number to dateUse the week strip to see the exact Monday-through-Sunday range.
ISO week-year calculatorHandle early January and late December dates that belong to a different ISO year.
53 week ISO yearSee whether the selected ISO week-year has 52 or 53 weeks.
Comparison

Why Use an ISO Week Date Converter Instead of a Calendar?

A normal calendar can show a date, but it usually does not explain ISO week-year boundaries or the YYYY-Www-D format.

TaskRandomly.onlineManual method
Date to ISO week dateShows YYYY-Www-D instantly.Requires manual week lookup.
Week number to dateConverts ISO year, week, and weekday back to a date.Needs a special ISO calendar view.
Boundary datesExplains January and December week-year cases.Easy to confuse with calendar year.
Batch conversionConverts many dates or ISO strings in one panel.Manual calendar lookup is slow.
Guide

How to Use ISO Week Date Converter

Choose conversion direction, enter a date or ISO week parts, and copy the result.

Choose the conversion direction

Use Date to ISO for normal dates, or ISO to Date when you already know the ISO week-year, week, and weekday.

Pick a calendar date

Use the custom calendar picker or type a date in YYYY-MM-DD format.

Adjust ISO week values

Use the custom year and week steppers, then choose Monday through Sunday using the weekday chips.

Review the result cards

Read ISO week date, calendar date, week range, ISO week-year, weekday, and 52 or 53 week-year status.

Batch convert if needed

Paste dates or ISO week strings one per line to convert multiple values without a mobile-breaking table.

Support

Frequently Asked Questions

What is an ISO week date?

An ISO week date is a date written with ISO week-year, week number, and weekday. The common format is YYYY-Www-D, where Monday is 1 and Sunday is 7.

How do I convert a date to ISO week date?

Choose Date to ISO, select a calendar date, and the converter returns the ISO week-year, week number, weekday, and complete YYYY-Www-D value.

How do I convert ISO week number to date?

Choose ISO to Date, enter the ISO week-year and week number, select weekday 1 through 7, and the tool returns the matching Gregorian calendar date.

What does YYYY-Www-D mean?

YYYY is the ISO week-year, W indicates week format, ww is the two-digit ISO week number, and D is the ISO weekday number from Monday 1 to Sunday 7.

Why can January dates belong to the previous ISO year?

ISO years are based on full weeks. Week 1 is the week containing January 4, so early January dates can still be part of the previous ISO week-year.

Can December dates belong to the next ISO year?

Yes. Late December dates can fall in ISO Week 01 of the next ISO year if the Monday-to-Sunday week crosses the boundary.

Which day is 1 in ISO week date?

Monday is ISO weekday 1. Tuesday is 2, Wednesday is 3, Thursday is 4, Friday is 5, Saturday is 6, and Sunday is 7.

Can an ISO year have 53 weeks?

Yes. Some ISO week-years have 53 weeks depending on how weekdays align with January 1 and December 31.

Is ISO week date the same as a normal week number?

Not always. ISO week dates use Monday starts and ISO week-year rules. Other week-number systems may start Sunday or count from January 1 differently.

Can I batch convert ISO week dates?

Yes. Paste YYYY-Www-D values or YYYY-MM-DD dates, one per line, and the batch converter returns matching results.

Do developers use ISO week dates?

Yes. ISO week dates are useful in APIs, logs, payroll systems, sprint planning, warehouse labels, and international reports where week-based dates are required.

Is my ISO week data uploaded?

No. The converter runs locally in your browser. Dates, ISO week values, batch input, and copied summaries are not uploaded.

Still have questions?

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