The IRR can then be calculated using the following formula, with 0.1 being the initial guess at the rate:
The IRR formula requires at least one negative and one positive value. Normally, the negative value at t=0 represents the initial investment. The future cash flows can be negative or positive, but they need to be periodic (occuring at t=1, t=2, t=3, etc). If you have non-periodic cash flows, you can use the XIRR formula.
Download an IRR Calculator for Excel.