The Excel Tbillprice function returns the price, per $100 face value, of a Treasury Bill.
The syntax of the function is:
Where the arguments are as follows:
settlement    The settlement date of the treasury bill (i.e. the date that the bill is purchased). 
maturity    The maturity date of the treasury bill (i.e. the date that the bill expires). 
pr    The treasury bill's percentage discount rate. 
Note that the supplied maturity date must be greater than, but no more than one year after the settlement date.
Note also, that these dates should be supplied to the function as either:
Warning: If you attempt to input text representations of dates into Excel functions, the interpretion of these can differ, depending to the date system and date interpretation settings on your computer.
The following spreadsheet shows the Excel Tbillprice function used to calculate the price, per $100 face value, of a treasury bill with settlement date 01Feb2017, maturity date 30Jun2017 and a discount rate of 2.75%:
A  B  

1  Settlement Date:  01Feb2017 
2  Maturity Date:  30Jun2017 
3  =TBILLPRICE( B1, B2, 2.75% ) 
This function returns the value 98.86180556.
I.e. a treasury bill with the above terms would be valued at $98.86.
Note that, in the above example:
For further examples of the Excel Tbillprice function, see the Microsoft Office website.
If you get an error from the Tbillprice function, this is likely to be one of the following:
#NUM!    Occurs if either:

#VALUE!    Occurs if either:
