Function : ISOWEEKNUM()

📘 Definition:

The ISOWEEKNUM() function returns the ISO week number for a given date.
According to the ISO 8601 international standard, a week starts on Monday, and week 1 is the week containing the first Thursday of the year.

In India, this function is very useful for:

• Tracking weekly reports, sales, or attendance

• Creating performance dashboards

• Summarizing data in weekly-based timelines

🧩 Syntax: =ISOWEEKNUM(date)


• date → A valid date or a cell reference containing a date.

🧠 Example (Indian Perspective):

✅ Explanation:

• The ISO system treats weeks consistently across years and avoids confusion around year-end overlaps.

• For example, 31-Dec-2025 may belong to week 1 of 2026, depending on which day it falls on.

🪜 Step-by-Step Breakdown:

1. If cell A2 = 15-Feb-2025

2. Formula → =ISOWEEKNUM(A2)

3. Excel checks ISO rules and returns 7, meaning that date falls in Week 7 of 2025.

🧠 Tip:

• WEEKNUM() and ISOWEEKNUM() are different:

  • WEEKNUM() lets you choose the week-start day.

  • ISOWEEKNUM() always assumes Monday as the first day and uses ISO standards.

• For consistent reporting between departments, prefer ISOWEEKNUM().

🎯 Why It’s Useful:

• To prepare weekly summaries (sales, attendance, production).

• To group transactions or records week-wise.

• To generate charts showing week-over-week growth.

🧑‍💻 Project Task 1: Weekly Sales Report Generator

👉 Tasks:

1. Use =ISOWEEKNUM(A2) to find each invoice’s week number.

2. Create a Pivot Table to summarize total weekly sales.

3. Add conditional formatting to highlight the highest sales week.

🧑‍💻 Project Task 2: Student Attendance Week Tracker

👉 Tasks:

1. Use =ISOWEEKNUM(A2) to categorize attendance by week.

2. Use a Pivot Table to count total “P” (Present) for each week.

3. Calculate attendance percentage:

    

   =COUNTIF(PresentCells,"P") / COUNTA(WeekDates)


4. Highlight weeks with less than 75% attendance.