ISO Week Converter
Convert between ISO 8601 week notation and calendar dates in both directions. Paste a week string like 2026-W26 to get the date range, or paste a date to get the week string. Just need today's week number? See Week Number.
ISO 8601 week date format
The ISO 8601 week date format has three forms:
2026-W26— the week itself (Monday to Sunday)2026-W26-1through2026-W26-7— a specific day within the week (1=Monday, 7=Sunday)W26— shorthand accepted by this tool, assumes the current year
These strings appear in PostgreSQL's EXTRACT(WEEK FROM ...), Java's DateTimeFormatter with YYYY-'W'ww, Python's %G-W%V strftime pattern, and many European scheduling and payroll systems.
Frequently asked questions
What is ISO 8601 week notation?
ISO 8601 represents a week as YYYY-Www — for example 2026-W26. You can append a day number (1=Monday to 7=Sunday) to pinpoint a specific day: 2026-W26-3 is Wednesday of week 26, 2026.
How do I convert a week number to a date?
Paste the ISO week string (e.g. 2026-W26) into the input above. The converter shows the Monday–Sunday date range and a copyable ordinal code for each day of that week.
How do I find the ISO week for a date?
Paste any date (2026-06-22, June 22 2026, a Unix timestamp, etc.) and the converter resolves it to the correct ISO week string and highlights that day in the table.
Why does the ISO week year sometimes differ from the calendar year?
ISO week 1 is defined as the week containing the year's first Thursday. This means January 1–3 can belong to the previous year's last week, and December 29–31 can belong to the next year's first week. The converter handles these boundary cases automatically.
Where is ISO week notation used?
ISO 8601 week dates appear in database schemas (PostgreSQL's EXTRACT(WEEK FROM ...), SQL Server's ISO_WEEK), scheduling systems, European payroll software, log file naming conventions, and some REST APIs that group data by week.