The XIRR function calculates the internal rate of return for a schedule of cash flows that is not necessarily periodic.

XIRR takes 2 required arguments and 1 optional argument:

Syntax: XIRR(values, dates, [guess]) ##### Using the XIRR function:  The arguments for the XIRR function are:
Argument Required? Description
values Required A series of cash flows that corresponds to a schedule of payments in dates. The first payment is optional and corresponds to a cost or payment that occurs at the beginning of the investment. If the first value is a cost or payment, it must be a negative value. All succeeding payments are discounted based on a 365-day year. The series of values must contain at least one positive value and one negative value.
dates Required A schedule of payment dates that corresponds to the cash flow payments. The first payment date indicates the beginning of the schedule of payments. All other dates must be later than this date, but they may occur in any order.
guess Optional A number that you guess is close to the result of XIRR. ##### Quite A few more things:
 • Excel stores dates as sequential serial numbers so they can be used in calculations. By default, January 1, 1900 is serial number 1, and January 1, 2014 is serial number 41640 because it is 41,640 days after January 1, 1900. • Numbers in dates are truncated to integers. • XIRR expects at least one positive cash flow and one negative cash flow; otherwise, XIRR returns the #NUM! error value. • If any number in dates is not a valid date, XIRR returns the #VALUE! error value. • If any number in dates precedes the starting date, XIRR returns the #NUM! error value. • If values and dates contain a different number of values, XIRR returns the #NUM! error value. • In most cases you do not need to provide guess for the XIRR calculation. If omitted, guess is assumed to be 0.1 (10 percent). • XIRR is closely related to XNPV, the net present value function. The rate of return calculated by XIRR is the interest rate corresponding to XNPV = 0. • Excel uses an iterative technique for calculating XIRR. Using a changing rate (starting with guess), XIRR cycles through the calculation until the result is accurate within 0.000001 percent. If XIRR can't find a result that works after 100 tries, the #NUM! error value is returned.

### Summary

The XIRR function calculates the internal rate of return for a schedule of cash flows that is not necessarily periodic.