Week Number Calculator
Enter a date to get its ISO-8601 week number, week start/end dates, and total weeks in that year.
ISO Week Number:
Week Start (Monday):
Week End (Sunday):
Total ISO Weeks in :
How to Use Week Number Calculator
- Select a date – the date picker defaults to today. Any valid date can be chosen.
- View the ISO week number – the tool instantly shows the ISO‑8601 week number, along with the Monday‑start and Sunday‑end dates of that week.
- Check total weeks in the year – it also displays how many ISO weeks the selected year has (52 or 53) – useful for payroll and financial planning.
- Expand the yearly week list – click “Show Week List” to see a table of every ISO week in that year with its start and end dates.
Benefits of Week Number Calculator
- Quickly find the ISO week number for any date – essential for project management, sprint planning, and MNC reporting cycles that use week numbers.
- The week start and end dates (Monday to Sunday) give you the full window for that week at a glance.
- Total ISO weeks display helps you plan annual budgets and timelines knowing whether the year has 52 or 53 weeks.
- The full‑year week table is collapsible, so you can look up any week without scrolling through a separate calendar.
Frequently Asked Questions
Why does my calendar show Week 1 starting on 1 January but this tool shows Week 53?
The ISO 8601 standard says Week 1 is the week that contains the first Thursday of the year. If 1 January falls on a Friday, Saturday, or Sunday, those days belong to the last week of the previous year (Week 52 or 53). This tool follows the ISO standard, which is used in India by IT companies and project management tools like Jira and Asana.
Is there an option to show US week numbering (Sunday start)?
Currently, the tool shows only ISO week numbering (Monday start). For US‑style week numbers, you would need to adjust the calculation, but the ISO standard is more widely adopted in India.
How do I find which week a particular project milestone falls in?
Select the milestone date in the date picker, and the tool instantly shows the ISO week number, week start (Monday), and week end (Sunday) for that date.
Is Week Number Calculator free and private?
Yes — it is 100% free, needs no sign‑up, and everything runs in your browser; your data never leaves your device.