Summary

The DAY function returns the day of the month from a date as a number from 1 to 31. It is useful when you only need the day part of a full date and want to ignore the month and year.

This comes up in recurring schedules, billing logic, reminders, and other formulas that care about a position inside the month instead of the full calendar date.

Syntax

=DAY(serial_number)

DAY takes one argument: a valid Excel date value. That value can come from a cell reference, a DATE formula, TODAY, or even a raw serial number.

If the input is a real date, DAY returns just the day part. For example, if the date is April 15, 2026, DAY returns 15.

Arguments

• serial_number - A valid Excel date value or something Excel can interpret as a date.

DAY vs Other Date Part Functions

DAY is one of several functions that extract one part of a date. The main difference is simply which part you want back.

The key point is that DAY does not tell you the weekday or the month. It only returns the day number inside that month.

Using DAY

The most common use of DAY is extracting a day number from a date that already exists in your worksheet. If the full date is important for storage, but the day number is important for logic, DAY gives you that one piece directly.

This is useful in formulas like billing reminders, due-date checks, monthly cutoffs, and recurring trigger dates. For example, if a task always happens on the 15th, you can test whether DAY(A1)=15.

• Use DAY when you only care about the 1-31 part of a date.
• Use it with DATE, TODAY(), or cell references that already contain dates.
• Use it with EOMONTH if you need month-end logic.

One helpful detail is that DAY can read raw Excel serial dates too. If the value is a valid date serial, Excel can still return the correct day number from it.

Example 1 - Extract the Day from a Date

This is the most basic use of DAY: return the day of the month from a normal date.

=DAY("2026-04-15")

This returns 15.

Example 2 - Use DAY with DATE

You can combine DAY with another date function if the date is built by formula instead of typed directly.

=DAY(DATE(2025,12,25))

This returns 25.

Example 3 - Read a Serial Date

Excel stores dates as serial numbers in the background, so DAY can also work on that raw value.

=DAY(46023)

If the serial is a valid date, DAY returns the matching day of the month.

Example 4 - Days Left This Month

DAY also works well with month-end formulas. One common pattern is comparing the current day with the last day of the month.

=DAY(EOMONTH(A1,0))-DAY(A1)

This returns the number of days left before the month ends.

Conclusion Recap

DAY is simple, but it becomes very useful once your formulas need to react to recurring positions inside a month. It gives you a clean way to pull just the day number without rebuilding the entire date logic around it.

• Core job: DAY returns the day of the month from a date.
• Main benefit: It isolates the 1-31 part of a date for monthly logic.
• Useful pairings: It works well with DATE, TODAY(), and EOMONTH.
• Practical use: It helps with reminders, billing cycles, and monthly cutoff formulas.
• Extra detail: It can also read valid Excel serial date values.