Guess is a number that you guess is close to the result of IRR.
Microsoft Excel uses an iterative technique for calculating IRR. Starting with guess, IRR cycles through the calculation until the result is accurate within 0.00001 percent. If IRR can't find a result that works after 20 tries, the #NUM! error value is returned.
In most cases you do not need to provide guess for the IRR calculation. If guess is omitted, it is assumed to be 0.1 (10 percent).
If IRR gives the #NUM! error value, or if the result is not close to what you expected, try again with a different value for guess.