Para usar a função RATE, você pode usar o seguinte:
nper = 8 //This is the number of periods for 2 years
Pmt = 0 //There are no payments being made till the end of the number of periods
Pv = 103.09//This is used to represent 103.09% of X
Fv = -105.06 //This is used to represent 105.06% of X
Type = 0 //Payment is at the end of the period
ou você pode fazer
=POWER(1.0506/1.0309,1/8) - 1