YEARFRAC Function
Calculates the fraction of the year represented by the number of whole days between two dates. Use the YEARFRAC worksheet function to identify the proportion of a whole year's benefits or obligations to assign to a specific term.
Syntax
YEARFRAC(<start_date>, <end_date>, <basis>)
Parameters
Term 
Definition 


start_date 
The start date in datetime format. 

end_date 
The end date in datetime format. 

basis 
(Optional) The type of day count basis to use. All arguments are truncated to integers.

Return Value
A decimal number. The internal data type is a signed IEEE 64bit (8byte) doubleprecision floatingpoint number.
Remarks
In contrast to Microsoft Excel, which stores dates as serial numbers, DAX uses a datetime format to work with dates and times. If you need to view dates as serial numbers, you can use the formatting options in Excel.
If start_date or end_date are not valid dates, YEARFRAC returns an error.
If basis < 0 or if basis > 4, YEARFRAC returns an error.
Example
The following example returns the fraction of a year represented by the difference between the dates in the two columns, TransactionDate and ShippingDate:
=YEARFRAC(Orders[TransactionDate],Orders[ShippingDate])
The following example returns the fraction of a year represented by the difference between the dates, January 1 and March 1:
=YEARFRAC("Jan 1 2007","Mar 1 2007")
Use fourdigit years whenever possible, to avoid getting unexpected results. When the year is truncated, the current year is assumed. When the date is or omitted, the first date of the month is assumed.
The second argument, basis, has also been omitted. Therefore, the year fraction is calculated according to the US (NASD) 30/360 standard.