Forward Pricing for Fixed Income Securities

John is considering entering a forward contract to buy a fixed income security. He is particularly interested in understanding how the price of a forward contract is determined for fixed income instruments.

A fixed income forward contract is used to lock in the price of a bond for future delivery. The pricing of a forward contract typically takes into account several factors, including the current spot price of the bond, the risk-free interest rate, and the time until delivery. The forward price can be calculated using the present value of the expected future cash flows of the bond.

Given this context, what is the primary factor that influences the forward price of a fixed income security?