This article examines the impact of inflation on the investment costs of a proposal that generates future income. When investing in investment proposals, the optimal solution cannot be reached if the value of inflation is not included in the estimates of the cash flow component, including the first component, which is the amount to be invested, so the estimates of future cash flows are modified to take into account the expected inflation rate. The values are calculated that represent the expected sensitivity of the net present value of the investment proposal to inflation. It is shown that the optimal amount of investment depends on the rate of inflation, and it will be higher, the greater the value of the net present value becomes when the inflation rate changes.