Date Add / Subtract Calculator
About ISO Week Date Converter
The ISO-8601 Week Date Converter translates standard calendar dates (YYYY-MM-DD) to ISO Week Dates (YYYY-Www-D, e.g. `2026-W42-4`), calculates ISO week numbers ($1-53$), ISO leap years (53-week years), and converts ISO week strings back to standard dates.
How to Use ISO Week Date Converter
Step 1
Enter a calendar date or type an ISO week date string (e.g. `2026-W42-4`).
Step 2
Review computed ISO year, ISO week number ($1-53$), and day of week ($1=\text{Mon}, 7=\text{Sun}$).
Step 3
Click "Copy ISO Week Date".
Practical Use Cases for ISO Week Date Converter
European Manufacturing & Supply Chain Logistics Week Numbering
Convert production batch delivery dates to standard European automotive and manufacturing ISO week codes (e.g. `KW 42`).
Enterprise ERP & Business Analytics Weekly Aggregations (SAP / SQL)
Generate standardized ISO week keys for SQL analytical queries and data warehouse weekly cohort aggregations without fractional week splits.
Input & Output Examples
Converting October 15, 2026 to ISO Week Date
Date: `2026-10-15`
ISO Week Date: `2026-W42-4` | ISO Year: `2026` | ISO Week: `42` | ISO Day of Week: `4 (Thursday)` | Total Weeks in 2026: `53`
Key Features & Performance
- ✓Bi-Directional Converter: converts Calendar Date $\leftrightarrow$ ISO Week Date (`YYYY-Www-D`).
- ✓ISO Leap Year Detection: identifies 53-week years (years starting on Thursday or leap years starting on Wednesday).
- ✓Developer Code Output: generates JavaScript, Python (`date.isocalendar()`), and SQL (`EXTRACT(ISOWEEK)`) conversion snippets.
- ✓100% Client-Side memory execution.
- ✓1-Click Copy ISO week date string.
Key Terminology & Definitions
ISO-8601 Week Date
An international standard date format represented as `YYYY-Www-D`, where YYYY is the ISO week-numbering year, W is the week designator, ww is the week number ($01-53$), and D is the day of week ($1-7$).
ISO Week 1
The week containing the first Thursday of the Gregorian year, or equivalently the week containing January 4th.