What this calculator does
Find out how long an investment takes to give you your money back. That time is called the payback period. A $25,000 machine that saves $6,000 a year pays for itself in a little over four years. A project that earns little at first and more later takes longer than its average would suggest.
Payback is easy to explain, and it favors projects that return cash quickly. That's why it's one of the most common first checks on any spending decision, from equipment to energy upgrades.
This calculator handles a steady cash flow or a list of different amounts for each period. It gives the payback in periods and, for yearly flows, in years and months. It also shows the total cash returned. Add a discount rate and it finds the discounted payback too. That version counts each future dollar at its present value, meaning what it's worth to you today. You'll also see the net present value (NPV) of the whole stream: everything it brings in, in today's dollars, minus the cost.
Where it's used
Why this math matters outside the classroom:
- Equipment purchases. A shop owner finds that a $25,000 machine saving $6,000 a year pays for itself in 25,000 ÷ 6,000, about 4.17 years.
- Home energy upgrades. A homeowner checks that a $2,400 heat pump water heater saving $400 a year pays back in 6 years.
- Small business plans. Founders estimate how many months of profit it takes to recover the cost of opening a second location.
- Classroom rate problems. Students treat yearly savings as a constant rate and work out how many years it takes to reach a total cost.
- Comparing projects. Managers rank two projects with the same cost by which one returns the money sooner, then check their NPVs.
Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 6.RP.A.3.b. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter the up-front cost.
- Choose whether the cash coming back is the same every period or different each period. Then enter the amount per period and how long it lasts, or the list of amounts in order.
- If you like, enter a discount rate to see the discounted payback and the net present value.
- Choose whether the periods are years or months. Then read the payback period and follow the running total in the table.
What the inputs mean
- Up-front cost
- Everything you pay at the start: purchase price, installation, setup and any other up-front costs.
- Net cash flow per period
- The net cash the investment brings in each period. That's the extra income or money saved, minus its own running costs such as maintenance or fees.
- Number of periods it lasts
- How many periods the cash flow continues. If the cost isn't repaid within this many periods, the calculator tells you so instead of guessing beyond them.
- Net cash flow for each period, in order
- One amount per period, starting with the first. A negative number is a period when the investment costs more than it brings in, such as a major repair.
- Discount rate per period (optional)
- The return you could earn elsewhere, per period. With monthly periods, enter a monthly rate. Leave it blank if you only want the simple payback.
Formula and method
equal cash flows: payback = cost ÷ cash flow per period uneven cash flows: payback = (k − 1) + amount still unrecovered after period k − 1 ÷ cash flow in period k discounted cash flow in period k = CFₖ ÷ (1 + r)^k discounted payback: the same rule applied to the discounted cash flows
Period k is the one in which the running total of cash flows first reaches the cost. CFₖ is the cash flow in period k, and r is the discount rate per period. The calculator assumes cash arrives evenly through each period. So it takes just the fraction of period k needed to cover what was still owed. With the same cash flow every period, this rule comes down to dividing the cost by the cash flow.
The simple payback treats a dollar you get in year five as worth the same as a dollar today. The discounted payback first shrinks each cash flow to its present value at your discount rate. So it's always at least as long as the simple payback. It may never be reached at all, even when the simple payback is.
Worked example
A business buys equipment for $25,000 that saves $6,000 a year for 10 years. Its required return is 8% a year.
- Simple payback: $25,000 ÷ $6,000 = 4.1667 years, which is 4 years 2 months.
- Discounted: the first five years of savings are worth $23,956.26 today at 8%, leaving $1,043.74 still to recover.
- Year 6's $6,000 is worth $6,000 ÷ 1.08^6 = $3,781.02 today. So the discounted payback is 5 + 1,043.74 ÷ 3,781.02 = 5.28 years.
- Over the full 10 years the savings total $60,000, and their net present value at 8% is $15,260.49.
Result: The equipment pays for itself in 4.17 years (5.28 years once the savings are discounted at 8%), with an NPV of $15,260.49.
Understanding the result
A shorter payback means your money is at risk for less time and comes back sooner for other uses. Many businesses set a limit, such as three or five years, and turn down projects that take longer. Compare the result with how long the investment will actually last. A payback close to the end of its useful life leaves little room for error.
Payback ignores everything after the break-even point. Two projects with the same four-year payback can differ greatly. One might keep producing cash for twenty years while the other stops at five. That's why payback works best alongside net present value or the internal rate of return (IRR), not instead of them.
If the discounted payback is much longer than the simple one, much of the return comes late. That's where the discount rate shrinks it most.
Assumptions and limitations
- The cost is paid at the start, and cash flows arrive evenly within each period.
- Discounting treats each period's cash flow as arriving at the end of the period, using one rate that never changes.
- The payback is the first time the running total reaches zero. Later negative cash flows can push the total below zero again.
- Results depend entirely on the cash flow estimates you enter.
- Taxes, financing costs and inflation aren't modeled unless you include them in the cash flows.
- Payback measures how fast you get your money back, not how profitable the investment is. Use the NPV and IRR calculators to compare total value.
Frequently asked questions
What is a good payback period?
It depends on the investment and how long it lasts. Small efficiency upgrades are often expected to pay back in a few years. Buildings and large equipment can justify longer periods. A useful rule of thumb: the payback should be comfortably shorter than the useful life. That leaves years of benefit after you've earned back the cost.
What's the difference between payback and discounted payback?
Simple payback adds up cash flows at face value. Discounted payback first converts each one to today's dollars using your required return. That reflects the fact that money you get later is worth less. The discounted version is always the same length or longer.
Why doesn't the payback period account for profit after break-even?
By design, it only measures how quickly the cost comes back. That makes it a good measure of risk and of how soon cash is free again. But it's a poor measure of total value. A project with a slightly longer payback can still be far more profitable over its life.
Can I use months instead of years?
Yes. Choose months and enter the cash flow per month. If you want discounting, enter a monthly discount rate. The payback is then shown in months.
How this calculator is checked
Method: Standard payback and discounted payback definitions with straight-line interpolation within the recovery period; end-of-period discounting at a constant rate, as in the NPV calculator. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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