Day Count with DAYS360 (30/360 Basis)

Excel Formulas › Date & Time

All versionsDAYS360

Bond and accounting math often assumes every month has 30 days and every year 360. DAYS360 counts days on that basis — giving the clean, standardized intervals that interest and accrual formulas expect.

Quick formula: for a start in B1 and end in B2:
=DAYS360(B1, B2)
DAYS360 treats each month as 30 days. From Jan 31 to Mar 31 it returns 60, not the 59 actual days.

Functions used (tap for the full reference guide):

DAYS360DATEDIF

The example

30/360 day counts compared with the actual calendar.

ABC
1StartEndDAYS360
21/1/202612/31/2026360
31/31/20263/31/202660
42/15/20263/15/202630

The formula

Days between two dates on a 30/360 basis:

=DAYS360(B1, B2) // Jan 1 → Dec 31 = 360 (a full 'year')

How it works

DAYS360 standardizes the calendar:

  1. Every month is treated as 30 days and every year as 360 — the convention used in many bond and accrued-interest calculations.
  2. It smooths out month-length differences, so monthly accruals are equal — handy for interest that’s quoted per 30-day month.
  3. A 3rd method argument toggles US (NASD) vs European day-count rules; omit it for the US default.
  4. For actual calendar days, just subtract: =B2-B1, or use DATEDIF(B1,B2,"d").

Which basis do you need? Use DAYS360 only when a contract or accounting standard calls for 30/360. For everyday “how many days” questions, the actual count (=B2-B1) is what you want.

Try it: interactive demo

Live demo

Compare 30/360 with the actual day count.

DAYS360:   Actual:

Variations

European basis

Set the method to TRUE:

=DAYS360(B1, B2, TRUE)

Actual days

Real calendar difference:

=B2 - B1

30/360 in years

Divide by 360 for a year fraction:

=DAYS360(B1, B2) / 360

Pitfalls & errors

Not the actual day count. DAYS360 is a financial convention, not a calendar count — don’t use it for “days until” or age math.

US vs European rules differ. The 3rd argument changes how month-ends (especially the 31st and Feb) are handled. Match the basis your contract specifies.

Real dates required. Like all date functions, DAYS360 needs date values, not text.

Practice workbook

📊
Download the free Day Count with DAYS360 (30/360 Basis) practice workbook
A 30/360 vs actual day-count comparison with US/European basis, year-fraction variant, plus 4 challenges with answers. No sign-up required.

Frequently asked questions

What does DAYS360 do in Excel?
It counts days between two dates assuming every month has 30 days and every year 360 — the 30/360 basis used in bond and accrued-interest math. =DAYS360(start, end).
How is DAYS360 different from subtracting dates?
Subtracting (=end-start) gives the actual calendar days. DAYS360 gives standardized 30-day months, so Jan 31 to Mar 31 returns 60 instead of 59.
What is the third argument for?
It selects US (NASD) vs European day-count rules for handling month-ends. Omit it for the US default; use TRUE for European.

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Related formulas: Days until a date · Exact age (y/m/d) · Effective interest rate

Function references: DAYS360 · DATEDIF