Payback period calculator (simple & discounted)

Payback Period Calculator — When Do You Break Even?

The payback period tells you how long it takes to recover your initial investment from the cash flows it generates. It's one of the oldest and most widely used capital budgeting metrics because it's intuitive, easy to communicate, and directly measures liquidity risk.

Simple Payback Period

For uniform cash flows: Payback = Initial Investment / Annual Cash Flow. For uneven cash flows, track cumulative cash flows period by period until the running total reaches zero. If the cumulative total crosses zero between periods, interpolate: Payback = prior full years + (remaining investment / next year CF).

Discounted Payback Period

Discounted payback uses the present value of each cash flow rather than raw amounts: PV(CF_t) = CF_t / (1+r)^t. Cumulative discounted cash flows take longer to recover the investment, giving a more conservative and accurate picture. A project with uniform $30,000 annual CFs on a $100,000 investment has a 3.3-year simple payback, but at 10% discount rate the discounted payback stretches to roughly 4.1 years.

Profitability Index

PI = NPV / Initial Investment + 1. A PI of 1.25 means you get $1.25 of present value for every $1.00 invested. PI > 1.0 = accept; PI < 1.0 = reject. When comparing multiple positive-NPV projects with a fixed capital budget, rank by PI to maximize value per dollar deployed.

Limitations

Payback period ignores cash flows after the payback date — a project that pays back in 3 years and then generates nothing is treated the same as one that pays back in 3 years and generates $1M more afterward. This creates a bias toward short-horizon, low-NPV projects. Always use payback alongside NPV, not as a replacement for it.

Applications

Payback period is used in capital budgeting for equipment, real estate improvements, energy efficiency upgrades, software development, and marketing investment evaluation. In SaaS, CAC payback (months to recover customer acquisition cost) is a critical growth efficiency metric tracked by investors and operators alike.