Week Number Calculator

Pick a date to see its ISO week number, the day of the year, and how many days remain — updated instantly.

⚡ Runs entirely in your browser

Pick a date above to see its week number.

ISO week number
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No date selected
Nothing calculated yet.
Weekday
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ISO week-year
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Weeks in year
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Day / total
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How the week number calculator works

Choose a date and every figure updates on the spot — no button to press, no waiting.

1

Pick a date

Use the date picker, or tap “Today” to jump straight to the current date.

2

Read the numbers

See the ISO week number, day of the year, days remaining, and the weekday instantly.

3

Copy when ready

Grab a tidy one-line summary with the Copy button — nothing is ever saved or sent anywhere.

What each figure means

ISO week number follows the ISO 8601 standard used across Europe and in business, banking and manufacturing. Weeks start on Monday, and week 1 is the week that contains the year’s first Thursday (equivalently, the week containing January 4). Because of that rule, the first few days of January can belong to the last week of the previous year, and the last days of December can belong to week 1 of the next year — which is why the ISO week-year sometimes differs from the calendar year.

Day of year counts from 1 on January 1 up to 365 (or 366 in a leap year) on December 31. Days remaining is how many days are left in the calendar year after the selected date, so December 31 shows zero. Weeks in year is either 52 or 53, depending on how the ISO calendar lands.

This tool is handy for planning sprints and payroll, reading “W‑numbered” calendars, and anyone coordinating schedules where the week number matters more than the exact date.

🔒

Private by design. Your chosen date never leaves your device. Every calculation happens right here in your browser — nothing is uploaded or stored.

Frequently Asked Questions

How is the week number worked out? ▼
It follows the ISO 8601 standard used across Europe and in business. Weeks start on Monday, and week 1 is the week containing the year's first Thursday (the same as the week that contains January 4).
Why can early January show week 52 or 53? ▼
Because of the ISO rule, the first few days of January can still belong to the last week of the previous year, and the last days of December can fall into week 1 of the next year. That's also why the "ISO week-year" can differ from the calendar year.
What does "day of year" mean? ▼
It counts the days from 1 on January 1 up to 365 — or 366 in a leap year — on December 31. "Days remaining" is how many days are left in the year after your chosen date.
Can a year have 53 weeks? ▼
Yes. Depending on how the calendar lands, an ISO year has either 52 or 53 weeks, and the tool shows which one applies to your selected date.
Does it use my time zone? ▼
The calculation is based purely on the calendar date you pick, so the week number is the same no matter where you are. Tap Today to jump to the current date.
Is my chosen date sent anywhere? ▼
No. Every figure is calculated in your browser — your date never leaves your device and nothing is uploaded or stored.

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