Bilgin's Blog | DAYS360 Function

I know that this is not a mainstream issue, but those who are familiar with Excel's DAYS360 function would know this problem.

Shortly, "DAYS360" is an Excel function that calculates the number of days between two dates, regarding that each month is composed of 30 days. This feature is generally used in financial markets.

While I was dealing with Bloomberg API integration with a C# code, I faced the problem. One of my friends shared his formula of calculating the correct interval. This is the way Bloomberg system calculates DAYS360 style date intervals :

        public static int CalculateDays360(DateTime d1, DateTime d2)
        {
            int years = d2.Year - d1.Year;
            int months = d2.Month - d1.Month;

            int dayNo1 = 0;
            int dayNo2 = 0;

            dayNo2 = d2.Day;
            dayNo1 = d1.Day;

            if (dayNo1 == 31) dayNo1 = 30;
            if (dayNo2 == 31) dayNo2 = 30;

            int days = dayNo2 - dayNo1;
            return years * 360 + months * 30 + days;
        }

Use it with your own risk.

I checked it with numerous date intervals of real Bloomberg data. It worked without exception.

But beware : It doesn't work the same way that Excel calculates it. But from internet forums, I understand that not all of the users are happy with Excel 's way of calculating DAYS360 either. Maybe our function helps you.

Here's a Visual Studio 2005 project, in which I demonstrate how to use it.

Snapshot of the program