I have a data set with dates in one columns and a price in the second colum corresponding to that date.

Not every date has a price, and the missing prices are not constant (ie no consistency in the number of days without a price)

Is there an easy formula to be able to interpolate the numbers?

Date______________Price
01/01/01__________100
01/02/01__________???
01/03/01__________???
01/04/01__________105
01/05/01__________???
01/06/01__________???
01/07/01__________???
01/08/01__________99