Help calculate excel formula

[spider0176]

Hi, help me to calculate an excel formula in PHP, it looks like
=(((1+((D7/100)*1.13))^D8)-1)

In my example
$D7=5.75 and $D8=12

and the calculation:
$op1=$D7/100;
$op2=$op1*1.13+1
$result=bcpow($op2, $D8)-1;

I tried many other way, but anyway result is different than excel's, it's 0 when D7 is small, any other ideas?

thanks,
Behrooz