How to Use DAY, DAYS and DAYS360 Function in Excel + Tips (Video in Khmer)

Hello everyone! Today i will show you how to use DAY, DAYS, and DAYS360 functions in Microsoft Excel step by step. Very easy and useful formulas for working with date calculations, counting days between dates, and accounting schedule!

1. What is DAY, DAYS, and DAYS360 Function in Excel?

• DAY: Extract the day number (from 1 to 31) from a specific date.
• DAYS: Calculate exact number of real calendar days between end_date and start_date.
• DAYS360: Calculate number of days between two dates based on a 360-day year (12 months x 30 days), commonly used in banking and financial accounting.

Think of them like date calculators:

• =DAY("2026-09-21") ➔ returns 21 (day number).
• =DAYS(B2, A2) ➔ returns exact real calendar days (e.g. 181 days).
• =DAYS360(A2, B2) ➔ returns financial accounting days (e.g. 180 days).

2. 🛠️ Formula Syntax & Parameters

=DAY(serial_number)
=DAYS(end_date, start_date)
=DAYS360(start_date, end_date, [method])

• serial_number: Required for DAY. The date from which to extract day number.
• end_date & start_date: Required for DAYS and DAYS360.
  • ⚠️ Notice argument order: DAYS takes (end_date, start_date), but DAYS360 takes (start_date, end_date)!
• [method]: Optional for DAYS360.
  • FALSE (or omit) = US (NASD) method (30/360).
  • TRUE = European method (30/360).

3. 📋 Practical Examples

Example Data Table (A2:B4)

Example 1: Extract Day of Month with DAY Function

To extract the day number from date in cell B4 (2026-09-21):

=DAY(B4)

👉 Result: Returns 21!

Example 2: Count Calendar Days Between Dates with DAYS Function

To calculate real calendar days between 2026-01-01 and 2026-07-01:

=DAYS(B2, A2)

👉 Result: Returns 181 days!

Example 3: Count Financial Accounting Days with DAYS360 Function

In 30/360 accounting method, 6 months (Jan 1 to Jul 1) is calculated as exactly 6 * 30 = 180 days:

=DAYS360(A2, B2)

👉 Result: Returns 180 days!

💡 Quick Tips for DAY, DAYS and DAYS360 Functions

1. Watch Out for Argument Order in DAYS vs DAYS360!
   • DAYS(end_date, start_date) put end date first!
   • DAYS360(start_date, end_date) put start date first!
   • If you put start date first in DAYS, it will return a negative number (e.g., -181).
2. DAYS Counts Leap Years Automatically: DAYS counts actual calendar days including February 29 on leap years, while DAYS360 treats every month as 30 days.
3. Calculate Days Remaining Until Deadline: =DAYS(deadline_date, TODAY()) shows how many days left until due date!
4. Fix #VALUE! Error: Make sure both date arguments are valid Excel date values, not text strings.

📚 Related Resources & Tutorials

• How to Use YEARFRAC Function in Excel
• EDATE vs EOMONTH Function in Excel
• Top 15 Basic Excel Formulas for Beginners ↗