Payback Period: Formula, Examples, and Limits

The payback period formula tells you how long it takes for a project's cash inflows to repay the money you put in. For even annual cash flows, it is the initial investment divided by the annual cash flow; for uneven flows, you add up the cash flows year by year until the total reaches the investment. Payback is simple, quick and easy to explain to owners and lenders, and it measures something real: how long your money is at risk. It also has a serious flaw, which is that it ignores what happens after the investment is recovered and the time value of money. This guide gives the formulas with worked examples, shows a case in which payback picks the wrong project, explains discounted payback and customer payback, and says how to use the measure sensibly. It is part of budgeting and forecasting, and sits with capital budgeting methods, net present value and internal rate of return. Its practical uses are covered below with capital allocation frameworks and WACC and hurdle rates for the broader decision.

The formulas

Even cash flows

Payback period = Initial investment / Annual cash inflow

Example. A machine costs $60,000 and saves $20,000 a year. Payback = 60,000 / 20,000 = 3.0 years.

Uneven cash flows

Add cumulative cash flows until they turn positive; in the year of recovery, take the fraction needed.

Payback = Years before recovery + (Unrecovered amount at start of the recovery year / Cash flow in the recovery year)

Example. A $100,000 project returns $30,000, $35,000, $40,000, $40,000 and $30,000.

Recovery happens in year 3. Payback = 2 + 35,000 / 40,000 = 2.875 years, about 2 years and 10.5 months.

In months

For monthly flows, use months as the unit: an investment of $12,000 and net monthly cash inflow of $1,500 pays back in 8 months.

Decision rule

Accept the project if payback is less than a maximum period set by the company (for example, three years). Among alternatives, a shorter payback is preferred. The limit should reflect how long you can tolerate the money being at risk, and the pace of change in the business.

Discounted payback

Discounted payback applies the same logic to present values of cash flows, so that it accounts for the time value of money. Using a 10 percent rate for the same project:

Discounted payback = 3 + 13,748 / 27,321 = 3.50 years, longer than the simple payback of 2.88 years. It is always longer, and it is infinite if the project's NPV is negative within its life.

Where payback goes wrong: a worked comparison

Two projects each cost $100,000, with a 10 percent required return.

• Project X returns $50,000, $50,000 and $10,000 in years 1 to 3, then stops.
• Project Y returns $30,000 a year for six years.

Payback prefers Project X, which recovers its cost a year earlier. But Project X barely returns more than it costs and loses value once discounting is applied, while Project Y adds about $30,700 of value. Payback ignored everything after the recovery date. Check the arithmetic for Project X: 50,000 / 1.1 = 45,455; 50,000 / 1.21 = 41,322; 10,000 / 1.331 = 7,513; total 94,290, minus 100,000 = -5,710. For Project Y: 30,000 × 4.3553 (the six-year, 10 percent annuity factor) = 130,658; minus 100,000 = +30,658.

The lesson is not to abandon payback but to use it as a risk and liquidity check, together with NPV or IRR, not instead of them.

Customer and campaign payback

Payback is also used for marketing and customer acquisition.

CAC payback (months) = Customer acquisition cost / Monthly gross profit per customer

Example. Acquiring a customer costs $450. The customer generates $30 a month of gross profit. Payback = 450 / 30 = 15 months. If the average customer stays 12 months, the business loses money on that customer on average; if the average stays 36 months, the customer earns about $630 of gross profit beyond the acquisition cost (36 × 30 - 450 = 630). Note that this ignores discounting and uses averages; segment customers where retention differs. See unit economics and SaaS revenue forecasting.

When payback is useful

When to be careful

Building payback into a decision

1. Estimate incremental, after-tax cash flows, including working capital.
2. Calculate simple and discounted payback.
3. Calculate NPV and IRR. See net present value.
4. Compare payback with your tolerance and the project's life.
5. Test downside cases: how much longer is payback if sales are 20 percent lower?
6. Decide, and record the assumptions.

Downside test. In the $60,000 machine example, if savings are 20 percent lower ($16,000 a year), payback lengthens from 3.0 to 60,000 / 16,000 = 3.75 years, a 25 percent increase. A 20 percent shortfall in savings stretches the payback by a quarter. See sensitivity analysis in financial models.

Payback and inventory or working capital projects

Payback is a natural measure for working capital initiatives: if reducing inventory costs $20,000 to implement and frees $80,000 of cash that earns a 10 percent financing saving, payback on the cost is quick. Distinguish a one-time cash release from a recurring benefit when you report it. For product companies, see demand planning and inventory optimization.

Common mistakes

• Using payback as the only criterion.
• Ignoring cash flows after the payback date.
• Forgetting taxes and working capital.
• Mixing accounting profit with cash flow.
• Setting the same payback limit for every project regardless of life.
• Using averages for customer payback when retention varies.
• Assuming the forecast cash flows are certain.

FAQs

What is the payback period formula?

For even cash flows, initial investment divided by annual cash inflow. For uneven flows, add cumulative cash flows until the investment is recovered and take the fraction of the final year.

What is a good payback period?

It depends on the industry, risk and your cash needs. Choose a limit that reflects how long you can tolerate the money being at risk.

What is discounted payback?

The time to recover the investment using the present values of cash flows. It is longer than simple payback.

Why is payback not enough to make a decision?

It ignores cash flows after recovery and, in its simple form, the time value of money. Use it with NPV or IRR.

How do I calculate customer payback?

Divide acquisition cost by monthly gross profit per customer.