Part of the free Module 5: Excel Formulas and Functions · Function 23 of 105 · Full Excel course
The Excel DAYS360 function returns the number of days between two dates based on a 360-day year of twelve 30-day months. This convention is used in bond markets, loan agreements and some accounting systems to simplify interest calculations. DAYS360 supports both the US (NASD) and European methods for handling dates that fall on the 31st of a month.
Syntax
=DAYS360(start_date, end_date, [method])Arguments
| Argument | Required / Optional | Meaning |
|---|---|---|
| start_date | Required | The first date of the period. |
| end_date | Required | The last date of the period. If it is earlier than start_date, the result is negative. |
| method | Optional | FALSE or omitted uses the US (NASD) method; TRUE uses the European method. The two differ only in how they treat the 31st day of a month. |
How DAYS360 works
Every month is treated as 30 days, so the difference is calculated as (years x 360) + (months x 30) + (day difference) after adjusting the day numbers. In the European method, any start or end date on the 31st becomes the 30th. In the US method, a start date on the 31st becomes the 30th; an end date on the 31st becomes the 30th only if the start date is the 30th or 31st, otherwise the end date is moved to the 1st of the next month. The US method also treats the last day of February as the 30th when the start date falls there. Because of these rules, =DAYS360("2026-01-01","2026-12-31") returns 360 with the US method and 359 with the European method.
Step-by-step example: accrued interest on a loan
- Enter the loan start date in A2 (1 March 2026) and the payment date in B2 (4 September 2026). Put the principal in C2 (100,000) and the annual rate in D2 (6%).
- In E2 enter
=DAYS360(A2,B2). The result is 183 days on the 30/360 basis (the actual calendar difference is 187). - In F2 enter
=C2*D2*E2/360. The accrued interest is 3,050. - Change E2 to
=DAYS360(A2,B2,TRUE)to see whether the European method changes the day count for these dates; here it does not, because neither date is a 31st.
Practical use cases
1. Bond accrued interest (30/360 US)
=Face*Coupon*DAYS360(LastCoupon,Settlement)/3602. Monthly rent proration
=MonthlyRent*DAYS360(MoveIn,EOMONTH(MoveIn,0)+1,TRUE)/30Adding 1 to the month end makes the count run to the first of the next month, giving a full 30 for a whole month.
3. Days in a fixed-rate period
=DAYS360(A2,B2,TRUE)European banks and many ISDA contracts specify the 30E/360 convention, which is the TRUE method.
4. Whole 30-day months between two dates
=INT(DAYS360(A2,B2)/30)Common mistakes and tips
- Using DAYS360 for real durations: it deliberately misstates calendar days. For deadlines, ages and project lengths use DAYS or DATEDIF.
- Omitting the method: the default is US (NASD). State TRUE explicitly when a contract specifies 30E/360 so the assumption is visible.
- #VALUE! error: a date argument is text Excel cannot read. Use real dates or ISO-format text.
- Negative results: the dates are in the wrong order; the function does not swap them.
- Documenting the basis: label the cell “30/360” so readers know why the number differs from the calendar count.
DAYS360 compared with DAYS, YEARFRAC and DATEDIF
DAYS and simple subtraction give actual calendar days and are correct for almost every non-financial task. YEARFRAC covers the same day-count conventions as DAYS360 and more: basis 0 is US 30/360, basis 4 is European 30/360, and bases 1 to 3 are actual-day methods, and it returns the result as a fraction of a year ready to multiply by an annual rate. In practice =YEARFRAC(A2,B2,0) equals =DAYS360(A2,B2)/360. DATEDIF returns complete calendar months or years and is unrelated to financial conventions. Use DAYS360 when a document explicitly requires a 30/360 day count and you want the day number itself; use YEARFRAC when you need the year fraction directly.
Related functions
- YEARFRAC: year fraction with selectable day-count basis.
- DAYS: actual calendar days between two dates.
- DATEDIF: complete years, months or days between dates.
- EOMONTH: month-end dates for proration periods.
- See all lessons in the Excel Formulas course.
Frequently asked questions
What is the difference between the US and European methods in DAYS360?
Both treat months as 30 days. The European method changes any 31st to the 30th. The US method does the same for the start date but moves an end date on the 31st to the 1st of the next month unless the start date is also the 30th or 31st.
Why does DAYS360 give a different result from subtracting the dates?
DAYS360 assumes every month has 30 days, so it ignores the real lengths of months. Subtraction and DAYS give actual calendar days.
When should I use DAYS360?
Only when a contract, bond or accounting policy specifies a 30/360 day-count convention. For all other date differences use DAYS, DATEDIF or NETWORKDAYS.
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