Why is a dollar to be received in the future worth less than

Why is a dollar to be received in the future worth less than a dollar to be received now?

Solution

This is becuase of the rise in the inflation over time, the inflation generally increase the prices and depreciates the value for the money. The inflation is bad for lenders and good for borrowers, when the inflation rises the borrowers repay the loan with less valuable dollar than the before so it is bad for the lenders and the opposite for the buyers.