What the payback period tells you
The payback period is the time an investment needs to earn back what it cost. It answers a simple and very practical question: how long is my money tied up before I break even? It is one of the simplest measures in capital budgeting and works for anything from a solar panel on a house to a new delivery van or a software license for a small business.
A short payback means the cash comes back fast, so the investment carries less risk from changes you cannot predict, and the money is free again for the next opportunity. It does not tell you how profitable the investment is overall. For that you need net present value or the internal rate of return, which the NPV and IRR calculator works out from the same cash flows.
The payback period formula
With the same cash flow every year, the formula is a single division. With uneven cash flows, you add them up year by year and find the year in which the running total crosses zero.
In the uneven formula, A is the last year in which the cumulative cash flow is still negative, B is the amount still missing at the end of that year, and C is the cash flow of the next year. B ÷ C is the share of that next year you need. This step is called interpolation, and it assumes the cash comes in evenly during the year. If your cash arrives as one payment at the end of each year, the investment is only paid back at the end of year A + 1.
Example with uneven cash flows
An investment of $50,000 brings in different amounts over six years. The simple columns add up the cash as it comes in; the discounted columns first turn each year into today’s money at 7% a year.
| Year | Cash flow | Cumulative | Discounted | Cumulative discounted |
|---|---|---|---|---|
| 0 | −$50,000 | −$50,000 | −$50,000.00 | −$50,000.00 |
| 1 | $10,000 | −$40,000 | $9,345.79 | −$40,654.21 |
| 2 | $14,000 | −$26,000 | $12,228.14 | −$28,426.06 |
| 3 | $16,000 | −$10,000 | $13,060.77 | −$15,365.30 |
| 4 | $15,000 | $5,000 | $11,443.43 | −$3,921.87 |
| 5 | $12,000 | $17,000 | $8,555.83 | $4,633.96 |
| 6 | $8,000 | $25,000 | $5,330.74 | $9,964.70 |
The cumulative cash flow is still −$10,000 after year 3 and positive after year 4. Year 4 brings $15,000, so you need $10,000 ÷ $15,000 = 0.67 of it. The payback period is 3.67 years, or 3 years, 8 months. With discounting, the break-even point moves out to 4.46 years, about 4 years, 6 months.
Simple vs discounted payback
The simple payback period treats a dollar received in year five like a dollar received today. That is convenient, but money has a time value: a dollar today can be invested and grow. The discounted payback period fixes that by dividing each year’s cash flow by (1 + r)t, where r is your discount rate and t the year. The discount rate is usually your cost of capital or the return you could earn elsewhere with similar risk.
Discounted payback is always longer than simple payback, and the gap grows with the rate. If the discounted cash flows never add up to the investment, the investment does not pay back in today’s money at all, which is the same as saying its net present value is negative at that rate. With monthly cash flows, the calculator converts your yearly rate r into the equivalent monthly rate (1 + r)1/12 − 1.
What payback does not show
- Cash after the break-even point. Two investments with the same 3-year payback look equal, even if one stops earning in year 4 and the other earns for another decade.
- Profitability. Payback is a measure of time, not of return. Use the ROI calculator for the total return, the CAGR calculator for a yearly growth rate, and NPV or IRR for investments with several cash flows.
- Size. A $5,000 upgrade and a $500,000 factory can have the same payback period.
- Later costs. A large repair or a cleanup cost in a later year can push the cumulative cash flow below zero again. The calculator counts the investment as paid back only once the total stays above zero, and tells you when it first crossed.
Tips for realistic numbers
- Use net cash flow: extra revenue or savings minus the extra costs the investment causes, like maintenance, insurance, energy or subscriptions.
- Include taxes if they matter for your decision. Depreciation itself is not cash, but it can lower the taxes you pay.
- Set the length to the realistic life of the investment. If the payback period is close to that life, there is little room for error.
- Try a pessimistic version. Lower the cash flows by 20% and see whether the payback is still acceptable.
How to use the payback period calculator
- 1Enter the initial investment and pick your currency.
- 2Choose the same cash flow every period, per year or per month, and how many years it lasts. Or choose different each year and list the cash flows, year 1 first.
- 3Add a discount rate for the discounted payback period, or leave it empty.
- 4Read the payback period in years and months, check the chart and the year-by-year table, and copy the result, the table or a link.
Frequently asked questions
What is a good payback period?
There is no single number. Compare the payback period with how long the investment lasts and with your own cutoff: a machine that pays for itself in 3 years and runs for 10 is very different from one that pays back in 9. You can also set a maximum payback for routine purchases and only look closer at projects that pass it.
How do I calculate the payback period with uneven cash flows?
Add up the cash flows year by year, starting from the negative investment, until the running total turns positive. Take the last year with a negative total, then add the amount still missing at its end divided by the cash flow of the next year. With an investment of $50,000 and a running total of −$5,000 after year 3, a year 4 cash flow of $15,000 gives 3 + 5,000 ÷ 15,000 = 3.33 years.
What is the difference between payback and discounted payback?
The simple payback period adds up the cash flows as they are. The discounted payback period first turns each year’s cash flow into today’s money at your discount rate, so later dollars count for less. It is always longer than the simple payback, and with a high enough rate an investment may never pay back in discounted terms.
Why does the payback period have months?
The calculator assumes cash comes in evenly during each year, so it can tell how far into the break-even year you recover the last dollar. A result of 4.17 years means 4 years and about 2 months. If your cash really arrives once at the end of each year, round up to the next whole year.
Is a shorter payback period always better?
Not always. Payback ignores everything that happens after the break-even point. A project that pays back in 2 years and then stops can be worth far less than one that pays back in 4 years and earns for 15 more. Use payback to judge risk and how fast cash comes back, and use NPV or IRR to judge how much an investment is worth.
Can the payback period be calculated with monthly cash flows?
Yes. Choose the same cash flow every period and switch to per month. The calculator then counts month by month and shows the result in years and months. For a discounted payback it turns your yearly discount rate into the equivalent monthly rate.