Goal: Analyze the date October 25, 2025.
WEEKDAY: Which day of the week (1-7)?
WEEKNUM: Which week of the year (1-52)?
Date: Oct 25, 2025 (Saturday)
Day of Week:
Sun
1
Mon
2
Tue
3
Wed
4
Thu
5
Fri
6
Sat
7
Ready...
💻 Formula Structure
=WEEKDAY(serial_number, [return_type])
- 1. Date: The date to check.
- 2. Type: 1 (Sun=1, Sat=7) is Default. Use 2 for Mon=1.
=WEEKNUM(serial_number, [return_type])
- 1. Date: The date to check.
- 2. Type: Determines when the week starts (Sun or Mon).
-- Select a function...
...
⚠️ Common Pitfalls
🚫 Mon vs Sun Start
By default, Excel thinks weeks start on Sunday (Return Type 1).
If your work week is Mon-Sun, use WEEKDAY(A1, 2). This makes Mon=1, Sun=7.
📅 ISO Week Numbers
For European standards (ISO 8601), use ISOWEEKNUM instead of WEEKNUM. It handles the "Week 1" definition differently near Jan 1st.