Week Number Calculator

Find the ISO week number, US week number, fiscal week, week-year, date range, day of year, and batch week numbers with custom date controls.

100% Browser-Based•Local Processing

Week Lookup Studio

Find a date's week number

Compare ISO 8601, US Sunday-start, and fiscal week logic with custom date controls and batch lookup.

Week Result

Week number--Choose a date to calculate week number.

Year progress appears after calculation.

Week system--
Week year--
Week range--
Day of year--
Quarter--
Year remaining--
No week number result yet.
🧩 RELATED TOOLS
ISO Week Date Day of Week Date Difference Calendar Generator Fiscal Year Business Days

Privacy Focused

🔒 Local Processing. Your data never leaves your device.

Instant Results

🌐 Fully Client-Side. Runs instantly in your browser.

No Signup

⚡ No accounts. No hassle. Just open and use.

Browser Based

🚀 Works right in your browser. No installs, no downloads.

Overview

Find ISO, US, and Fiscal Week Numbers for Any Date

Week numbers are used in project plans, logistics, manufacturing schedules, sprint reports, payroll calendars, fiscal reporting, and international business communication. The problem is that week systems are not universal: ISO weeks start Monday, US week numbers usually start Sunday, and fiscal weeks depend on a company calendar.

Direct answer: Enter any date to find its ISO 8601 week number, US week number, or fiscal week number. The result includes week-year, week date range, day of year, quarter, year progress, and batch week lookup.

Use this page for searches like week number calculator, what week is it, current week number, ISO week number calculator, date to week number, US week number, and fiscal week calculator. For ISO week-date formatting, use the ISO Week Date Converter.

Week Number Calculator with custom date picker, ISO US and fiscal week chips, fiscal start controls, week number result, week date range, year progress bar, and batch week lookup panel
The Week Number Calculator explains ISO, US, and fiscal week numbers with custom controls, week date ranges, year progress, and batch date lookup.
Features

Week Number Features for Reports and Schedules

Custom date pickerChoose a date from a branded calendar overlay instead of a native browser picker.
ISO and US systemsSwitch between ISO Monday-start weeks and US Sunday-start weeks.
Fiscal week modeChoose common fiscal starts such as January, April, July, or October.
Week range outputSee the start and end dates for the selected week system.
Batch week lookupPaste multiple dates and get week numbers without a wide mobile-breaking table.
Copyable resultCopy the week number, system, week year, date range, day of year, and quarter.
Use Cases

Week Number Keywords Covered by Practical Examples

These blocks target the common ways users search for week-number answers across ISO, US, current-week, and fiscal reporting intent.

week number calculatorFind the week number for any selected date.
what week is itUse the Today preset to answer the current week number instantly.
current week numberThe default date is today and updates the ISO week result immediately.
ISO week number calculatorISO mode follows Monday-start ISO 8601 week-year rules.
date to week numberType or pick a date and convert it into a week number plus week range.
fiscal week calculatorFiscal mode supports common fiscal-year starts for internal reporting calendars.
Comparison

Why Use a Week Number Calculator Instead of a Calendar?

Calendars show dates, but they often hide week-year differences, ISO rules, and fiscal week definitions.

TaskRandomly.onlineManual method
Current week numberToday preset gives the answer instantly.Requires finding a week-number-enabled calendar.
ISO week-yearShows ISO week and week-year together.Manual calendars often confuse late December and early January.
US week numberSwitches to Sunday-start week logic.Requires a separate calendar system.
Batch lookupConverts multiple dates in one compact panel.Manual lookup is repetitive and error-prone.
Guide

How to Use Week Number Calculator

Choose a system, pick a date, and review the week number and date range.

Choose the week system

Select ISO 8601, US week, or Fiscal week with the custom chips.

Pick a date

Use the custom calendar picker or type a date in YYYY-MM-DD format.

Set fiscal start if needed

For fiscal week mode, choose January, April, July, or October fiscal start.

Read the result cards

Review week number, week-year, week range, day of year, quarter, and remaining days.

Use batch lookup

Paste multiple dates one per line to calculate many week numbers quickly.

Support

Frequently Asked Questions

What week number is today?

Use the Today preset. The calculator shows the current week number based on the selected ISO, US, or fiscal system.

What is an ISO week number?

ISO 8601 weeks start on Monday. Week 1 is the week containing the first Thursday of the year, which means some early January dates can belong to the previous ISO week-year.

What is the difference between ISO and US week numbers?

ISO weeks start Monday and use ISO week-year rules. US week numbers commonly start Sunday and count weeks from the Sunday containing January 1.

Why can a date in January show the previous ISO year?

ISO week-year is based on week boundaries, not only the calendar year. Early January dates can fall in the last ISO week of the previous year.

Can I calculate fiscal week numbers?

Yes. Choose Fiscal week and select a fiscal start month such as January, April, July, or October.

Can I batch calculate week numbers?

Yes. Paste dates in YYYY-MM-DD format, one per line, and the batch panel returns week numbers for valid dates.

Can I find the week date range?

Yes. The result includes the start and end dates of the selected week system.

Does the calculator show day of year?

Yes. The result includes day of year, quarter, and remaining days in the calendar year.

Is my date uploaded?

No. Week-number calculations and batch lookup run locally in your browser.

Can I copy the week result?

Yes. Use Copy Summary to copy the date, week number, week system, week-year, week range, and supporting facts.

Which week system should I use for business reports?

International reports often use ISO 8601. US-based teams may use Sunday-start weeks. Company reporting may use fiscal weeks.

What is a 53-week year?

Some ISO, US, or fiscal calendars can have 53 weeks depending on how weekdays align with the start and end of the year.

Still have questions?

If you cannot find the answer you are looking for, contact our support team.

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