Year Fraction (Returns the year fraction representing the number of whole days between start_date and end_date)

What does it to?
This function calculates the difference between two dates and expresses the result
as a decimal fraction.
Syntax
=YEARFRAC(StartDate,EndData,Basis)
Basis : Defines the calendar system to be used in the function.
0 : or omitted USA style 30 days per month divided by 360.
1 : 29 or 30 or 31 days per month divided by 365.
2 : 29 or 30 or 31 days per month divided by 360.
3 : 29 or 30 0r 31 days per month divided by 365.
4 : European 29 or 30 or 31 days divided by 360.
Formatting
The result will be shown as a decimal fraction, but can be formatted as a percent.
Example:
The following table was used by a company which hired people on short term contracts for a part of the year.
The Pro Rata Salary which represents the annual salary is entered.
The Start and End dates of the contract are entered.
The =YEARFRAC() function is used to calculate Actual Salary for the portion of the year.

Note:
The extra 1 has been added to the End date to compensate for the fact that the =YEARFRAC()
function calculates from the Start date up to, but not including, the End date.