How do you calculate the payback period for a customer ROI case?
Short answer
Build a net cash flow for each year, then keep a running total starting from year 0. Payback happens in the first year the running total turns positive. Inside that year, months to payback equal 12 × (full years before it + the unrecovered balance ÷ that year's net cash flow). If the total never turns positive, report that payback falls outside the horizon.
Payback answers a buyer's first question: how long until the investment has paid for itself? It ignores what happens afterward, so show it next to ROI and NPV and not instead of them.
What is the payback formula?
- Net cash flow for each year = benefits − costs, with one-time costs in year 0.
- Cumulative net cash flow = the running total from year 0.
- In the first year t where the cumulative total turns positive: payback in months = 12 × ((t − 1) + unrecovered balance at the start of year t ÷ net cash flow in year t).
What does a worked example look like?
A customer pays 90,000 up front for a monitoring system and expects net benefits of 40,000 in year 1 and 55,000 in year 2.
| Year | Net cash flow | Cumulative |
|---|---|---|
| 0 | −90,000 | −90,000 |
| 1 | 40,000 | −50,000 |
| 2 | 55,000 | 5,000 |
The total turns positive in year 2, with 50,000 unrecovered at its start. Payback = 12 × ((2 − 1) + 50,000 ÷ 55,000) = 12 × 1.909 = 22.9 months.
Why does payback alone mislead?
Payback ignores everything after the break-even point and does not discount cash flows. A project that pays back in 22.9 months but fades in year 3 can be worth less than one that pays back in 30 months and grows. Pair it with the net present value of the cash flows, which discounts each year, and with the ROI over the horizon. The same data feed all three.
What should a customer-facing model state?
State where each benefit comes from, who supplied the figure, and the adoption ramp: benefits rarely start at full value in year 1. A benefits figure is the customer's estimate, and the model only does arithmetic on it. Say so plainly in the document you hand over.
The customer ROI calculator computes ROI, NPV, IRR and payback in months from one-time costs, recurring costs and an adoption ramp. To compare options, use the total cost of ownership comparison.