Substitute the expected cash flow, discount rate and year into the equation PV = x / ((1 + r) ^ n) for each year an investment is expected to be held. PV is present value; x is the cash flow received at the end of the year; r is the discount rate; and n is the year. Cash flows may be negative. For example, $100 received at the end of year one with a 10 percent discount rate equals 100 / ((1 + 0.1) ^ 1).

Calculate the present value of the first year's cash flow by pressing "100," divide button, "(," "(," "1," "+," "0.1," ")," "^," "1," ")" and "=" on the calculator. This equals $90.91.

Calculate the present value of $100 received at the end of the second year by pressing "100," divide button, "(," "(," "1," "+," "0.1," ")," "^," "2," ")" and "=" on the calculator. This equals $82.64.

Calculate the sum of the present values of the cash flows received in years one and two by pressing "90.91," "+," "82.64" and "=" on the calculator. This equals $173.55.

Subtract a $150 initial investment cost from the sum of the present values of the cash flows by pressing "173.55," "-," "150" and "=" on the calculator. This equals $23.55, which is the NPV of a two-year investment with a 10 percent discount rate, $150 initial cost and $100 in cash flows at the end of each year.