Week Number Calculator

Find week of the year, get dates by week number, and calculate week differences

ISO 8601 Standard | Week starts Monday
Date to Week Number
Select Date
Week Number to Date
Week Number
Year
Current Week Information
Week Difference Calculator
Start Date
End Date
Year Overview - All Weeks
Select Year
ISO 8601 Standard
Week numbers follow international standard (Monday to Sunday)
Week Difference
Calculate exact number of weeks between any two dates
Year Overview
View all weeks in a year with start and end dates

Frequently Asked Questions

How is week number calculated?
Week numbers follow ISO 8601 standard. Week 1 is the week that contains the first Thursday of the year. Weeks start on Monday and end on Sunday.
What is the difference between ISO week and US week?
ISO weeks start on Monday, US weeks start on Sunday. This calculator uses ISO 8601 standard (Monday-Sunday) for international consistency.
How many weeks in a year?
Most years have 52 weeks, but some years have 53 weeks. It depends on when the first Thursday falls. This calculator handles both correctly.
Can weeks cross between years?
Yes! Week 1 of 2025 may start in December 2024. This calculator correctly handles week-year boundaries.
week number calculator week of the year ISO week number date to week week to date week difference calendar week

Week Number Calculator - Find Week of the Year

Our Week Number Calculator helps you find the ISO week number for any date, convert week numbers to date ranges, calculate weeks between dates, and view complete year overviews.

Features: Date to week number conversion, week number to date range, week difference calculator, current week info, and full year overview with all week start/end dates.

Perfect for: Project planning, academic scheduling, business reporting, payroll calculations, and any scenario requiring week-based date calculations.

ISO 8601 Standard: Week 1 is the week with the first Thursday of the year. Weeks run Monday through Sunday.