THE NUMORIX GUIDE
How to use the IRR Calculator
Last reviewed September 14, 2026
What this calculator does
The engine treats the comma-separated first cash flow as time 0 and each later value as the next equal period.
Formula and method
The engine treats the comma-separated first cash flow as time 0 and each later value as the next equal period. It uses Newton iteration on NPV = sum(CF_t / (1+r)^t), updating the rate with the NPV derivative until the change is small, then reports that rate and NPV evaluated at it.
Variables and inputs
Enter signed cash flows separated by commas, with the initial investment normally negative at year 0. Each following value is one equal period later; the route does not ask whether periods are months or years. Results are IRR percent and NPV in the same currency units as the flows.
Worked example
For cash flows -1000, 600, 600, the equation is -1000 + 600/(1+r) + 600/(1+r)^2 = 0. Let x = 1+r: 1000x^2 - 600x - 600 = 0, giving x about 1.1307 and r about 13.07%. At that rate the discounted inflows approximately equal the $1,000 outflow, so NPV is approximately $0.
How to interpret the result
IRR is a rate that makes the entered periodic cash flows break even in present-value terms. It is useful only when the cash-flow timing and reinvestment assumptions fit the decision. A positive IRR does not mean the investment is attractive without a required return or risk comparison.
Common mistakes to avoid
Put the initial outflow at time 0 and use the correct sign for later contributions or withdrawals. Do not mix monthly and annual cash flows in one list. Review unusual sign changes because they can create multiple roots or make Newton iteration unstable.
Assumptions and limitations
The route assumes equally spaced periods, uses a Newton solver with one starting rate, and does not select among multiple possible IRRs. It does not model taxes, fees, interim reinvestment, inflation, or irregular dates; the NPV display is evaluated at the numerical result rather than at a user-entered discount rate.