The payback period is calculated by counting the number of years it will take to recover the cash invested in a project.
Let's assume that a company invests $400,000 in more efficient equipment. The cash savings from the new equipment is expected to be $100,000 per year for 10 years. The payback period is 4 years ($400,000 divided by $100,000 per year).
A second project requires an investment of $200,000 and it generates cash as follows: $20,000 in Year 1; $60,000 in Year 2; $80,000 in Year 3; $100,000 in Year 4; $70,000 in Year 5. The payback period is 3.4 years ($20,000 + $60,000 + $80,000 = $160,000 in the first three years + $40,000 of the $100,000 occurring in Year 4).
Note that the payback calculation uses cash flows, not net income. Also, the payback calculation does not address a project's total profitability. Rather, the payback period simply computes how fast a company will recover its cash investment.