Solverly

Week Number Calculator

See the exact week of the year for any date—or the dates that fall within a specific week—at a glance. The Week Number Calculator is handy for sprint planning, payroll cycles, shipping cutoffs, academic terms, and fiscal reporting where consistent “week of year” labeling matters.

Enter a date to get its ISO-style week number, or choose a week to reveal its start and end dates so schedules, handoffs, and deadlines line up across teams and tools. The goal is clear coordination: standardized weeks that make it easy to plan events, track progress, and communicate timelines without confusion.

Enter any date to see its ISO week number, week-year, and the exact start/end of that week.

Enter date

Example: 09-03-2025

Enter a valid date in MM-DD-YYYY.

Summary

ISO week
—
ISO week-year
—
Week start (Mon)
—
Week end (Sun)
—

ISO weeks run Monday–Sunday. Week 01 is the week containing the year’s first Thursday.

We compute the **ISO week** for any date and show the week’s **Monday–Sunday range**. This is handy for sprint planning, academic syllabi, and reporting systems that key off week numbers.

Results interpretation

  • W01–W52/53: The ISO week label for the input date.
  • Week-year: The ISO year the week belongs to (can differ from the date’s calendar year).
  • Start/End: Monday and Sunday of that week in MM-DD-YYYY.

How it works

We apply ISO-8601 rules so results match scheduling software and international calendars.

Formulas, steps, assumptions, limitations

Week/year: Move the input date to the Thursday of its week, then count weeks since the year’s first Thursday.

Range: Compute the Monday of the same week and add 6 days to get Sunday.

Edge cases: Dates near New Year’s may belong to the previous/next week-year. We follow ISO rules consistently.

Use cases & examples

Sprint & release planning

Map tasks to W01–W52/53 to match engineering sprints and reporting periods.

Academic calendars

Align readings and assignments to ISO weeks for cross-country programs.

Payroll & logistics

Use the Monday–Sunday range to frame cutoffs, shipping cycles, or staffing plans.

FAQ: ISO week numbers

What date format should we use?
Enter dates as MM-DD-YYYY (for example, 09-03-2025).
What is an ISO week and week-year?
ISO weeks start on Monday, and Week 01 is the week containing the year’s first Thursday. The week-year can differ from the date’s calendar year near New Year’s.
Why does the week-year sometimes differ from the input date’s year?
Dates near year boundaries can fall in the previous or next ISO week-year depending on where the week’s Monday–Sunday range lands.
Do we use Monday–Sunday or Sunday–Saturday?
We use Monday–Sunday per ISO-8601 and display that range.
Can we jump to the same week next year?
Yes—navigate to a future date with our Date Calculator or Day of Week Finder, then check its week number here.
Do leap years change ISO weeks?
Leap days can shift boundaries, but the ISO rules still apply consistently.

How to find the ISO week for a date

Enter a date in MM-DD-YYYY to see its ISO week label, week-year, and Monday–Sunday range.

  1. Enter a date in MM-DD-YYYY (e.g., 09-03-2025).
  2. Review the ISO week number and the associated week-year.
  3. Use the displayed Monday and Sunday to see the week’s exact span.
Tools
  • Calendar (optional)
  • Our Copy link button to share inputs
Tips
  • Week numbering helps when schedules reference “W34” etc.
  • Pair with Business Days to exclude weekends/holidays for work plans.

Working with ISO weeks in planning and reporting

We use ISO weeks to coordinate across teams and regions because they provide a single, unambiguous week label. When a date maps to W01–W52/53, everyone knows which Monday–Sunday range we mean, even around New Year’s.

Why ISO-8601 became the default

Software, manufacturing, logistics, and education benefit from a consistent weekly cadence. Monday starts, numbered weeks, and a clear rule for Week 01 reduce misunderstandings in cross-border schedules.

Practical workflow

Convert a deadline to its ISO week, share the week label, and align tasks or meetings accordingly. Use the Monday–Sunday range to set clear start and cutoff dates for your plan.

Boundary quirks to remember

Some years include W53. Near the year boundary, the week-year can differ from the calendar year; our output shows both the week label and its range so plans are concrete.