IRR and XIRR, different results... why?!?!?!

[loremtz]

Hello everyone!
I am calculating IRR and XIRR but I get different results.

I know IRR is used to calculate periodic payments and XIRR is used for irregular payments. So I did a spreadsheet with monthly payments, I calculate both IRR and XIRR and got different results.
I have already changed IRR to effective annual, but still they are not the same...

here are my values: (hope someone can help!)


20-jun-10 ------------------- (900,000)
20-jul-10 -------------------- 7,300
19-ago-10 -------------------- 7,300
18-sep-10 -------------------- 7,300
18-oct-10 -------------------- 7,300
17-nov-10 -------------------- 7,300
17-dic-10 -------------------- 7,300
16-ene-11 -------------------- 7,300
15-feb-11 -------------------- 7,300
17-mar-11-------------------- 7,300
16-abr-11 -------------------- 7,300
16-may-11 -------------------- 7,300
15-jun-11 -------------------- 7,300
15-jul-11 -------------------- 7,300
14-ago-11 -------------------- 7,300
13-sep-11-------------------- 7,300
13-oct-11 -------------------- 7,300
12-nov-11 -------------------- 1,007,300

(dates are all +30)

IRR= 18.083%
XIRR= 18.356%

Thank you for your help!