When calculating internal rate of return you can use the provided calculator on your
series of cash flows. The IRR formula is built into the calculator.

You will see two series of cash flows. Each series of cash flows support the
IRR result at the bottom. To obtain a IRR for your cash flows, you need to supply
the actual cash flows from your project. Be sure to clear
out the numbers to zero for the years not needed. The year column can be changed
by just changing the first year.

Summary

Once you have finished calculating internal rate of return for each of your projects, you
can make a rational decision about which project is most economical for your
situation. Warning! The IRR found may not be valid if the cash flows
swing back and forth from positive to negative values. It is possible to have
more than one IRR answer in that case.