Calendar
Week calculator
Find the ISO week number and week-year for any date.
How to use this calculator
Enter Date. Find the ISO week number and week-year for any date. The answer updates when you change an input.
Understanding the result
ISO week-years can differ from calendar years around late December and early January.
Common questions
What assumptions does this result use?
Uses ISO 8601 Monday-based week numbering.
Are intermediate values rounded?
No. The calculation retains JavaScript number precision internally and formats only the displayed result unless the stated method requires a discrete whole value.