I have an out flow and then monthly inflows for a month. They are the same time every month the first of the month. When I use IRR I get 18%, when I use XIRR I get 640%. If i multiply 18% by 12 I get 217% which seems right ,but doesn;t take into account compounding. If use this =(iRR(C4:C16)+1)^12-1) I get 633% which is very close to 640% but seems way to high. I haven't even tripled my investment, which was -130,000 while making 440,00 total over the year. Can someone tell me which number is correct and why?