Week Number Calculator

Week Number Calculator features

• 01

  Today's week, front and centre

  The current week number, its week code and its exact date range are shown at the top, with the day of the year, the quarter, weeks left in the year and year progress underneath — an instant answer to "which week are we in?" without digging through a calendar.

• 02

  Date ↔ week, both ways

  Convert a specific date to its week number and year, or enter a year and week to get the exact date range it covers. Previous week, next week and today buttons let you step through the calendar, and every result copies in one click for sprints, payroll or reports.

• 03

  Month view, year grid and custom week counts

  A month calendar shows week numbers alongside each row and highlights today — click any day or week number to inspect it. A full-year grid lists all 52 or 53 weeks with their dates, and a start-date counter gives you semester teaching weeks, sprint weeks or weeks since any milestone.

Week Number Calculator FAQ

What week number is it right now?

The current week is displayed at the top of the tool as soon as it loads, using ISO 8601 by default, together with its date range and week code. Switch to US numbering if your calendar or organisation counts weeks from Sunday and January 1.

How is the ISO 8601 week number defined?

ISO weeks start on Monday, and week 1 is the week containing the year's first Thursday (equivalently, the week with January 4). This means early January can fall in the last week of the previous year, which the calculator handles correctly.

Why do ISO and US week numbers sometimes differ?

US numbering starts weeks on Sunday and puts January 1 in week 1, while ISO starts on Monday and anchors week 1 to the first Thursday. Around the new year the two systems can give different numbers for the same date.

How do I find the dates for a given week number?

Enter the year and week number in the week-to-date section and the tool shows the start and end dates of that week, following whichever numbering standard you've selected. You can also click any week in the month view or the full-year grid.

How do I count weeks from a start date, like a semester or project?

Use the start-date section: set the first day of your semester, sprint or project, then pick the date you're interested in. The tool numbers the weeks from there, with week 1 being the week that contains the start date — the same way schools count teaching weeks.

Can a year have 53 weeks?

Yes. Under ISO 8601 a year has 53 weeks when January 1 (or December 31 in a leap year) falls on a Thursday. The calculator accounts for this, so the year grid shows 52 or 53 weeks as appropriate.