MS Excel: DAYS360 function for day count calculations of financial modelling

The DAYS360 function in Excel calculates the number of days between two dates based on a 360-day year (12 months of 30 days). This function is primarily used in financial and accounting applications, such as calculating accrued interest, loan schedules, and bond pricing—where many conventions assume a 360-day year for simplicity.

This approach provides consistency in interest calculations and amortization models where exact calendar days may not be necessary or desirable.

Syntax

=DAYS360(start_date, end_date, [method])

Parameters:

Argument	Description
start_date	Required. The starting date of the period. Must be a valid Excel date.
end_date	Required. The ending date of the period. Must be a valid Excel date.
method	Optional. A logical value:
	FALSE or omitted – Uses the US (NASD) method (default).
	TRUE – Uses the European method.

Returns: An integer representing the number of days between two dates, assuming a 360-day year.

Examples

Formula	Result	Explanation
=DAYS360("2025-01-01", "2025-12-31")	360	One full year using 360-day method
=DAYS360("2025-02-28", "2025-03-31")	30	Handles February to March transition cleanly
=DAYS360("2025-02-28", "2025-03-31", TRUE)	30	European method treats end dates differently
=DAYS360(A2, A3)	Varies	Assumes A2 is start date and A3 is end date

In financial contexts, using 360 days simplifies month-based interest accruals and makes year-to-year comparisons easier.

US vs European Methods

Feature	US (NASD Method)	European Method
Default setting in Excel	Yes	No (must set method to TRUE)
End-of-month handling	Adjusts end dates falling on 31st or Feb 28	Keeps original dates as-is
Use case	Common in US-based finance	Common in European financial standards

Use Cases

Scenario	How DAYS360 Helps
Loan interest calculations	Predictable day counts simplify calculations
Bond pricing and settlement modeling	Follows 30/360 convention used in fixed income
Amortization schedules	Keeps monthly intervals consistent
Lease accounting	Used for accurate monthly liability tracking

Notes

• Both dates must be valid Excel date values.

• If start_date is later than end_date, the result will be negative.

• DAYS360 is particularly useful when exact calendar day counting is not required but monthly uniformity is desired.

Related Functions

Function	Description
DAYS()	Counts actual days between two dates
DATEDIF()	Flexible function for date difference in units
YEARFRAC()	Returns fractional years between dates
EOMONTH()	Returns end of the month after a given offset
NETWORKDAYS()	Counts working/business days between two dates

Summary

Feature	Description
Function Name	DAYS360
Purpose	Calculates number of days using 360-day year
Common Use	Finance, loans, accounting, bond interest
Optional Method	US (default) or European
Return Type	Integer (positive or negative)
Excel Version	Available in all modern Excel versions

Final Thoughts

The DAYS360 function is a financial modeling essential, streamlining calculations where uniform day counts matter more than actual calendar variability. Whether you’re building amortization schedules or investment models, using DAYS360 ensures consistent and predictable results.